Efficient and Stable Luminescence from Mn2+ in Core and Core-Isocrystalline Shell CsPbCl3 Perovskite Nanocrystals

Photon Management Through Energy Transfer in Halide Perovskite Nanocrystal-Dye Hybrids: Singlet vs Triplet Tuning

ConspectusPhotoinduced energy and electron transfer processes offer a convenient way to convert light energy into electrical or chemical energy. These processes remain the basis of operation of thin film solar cells, light emitting and optoelectronic devices, and solar fuel generation. In many of these applications, semiconductor nanocrystals that absorb in the visible and near-infrared region are the building blocks that harvest photons and initiate energy or electron transfer to surface-bound chromophores. Such multifunctional aspects make it challenging to steer the energy transfer pathway selectively. Proper selection of the semiconductor nanocrystal donor requires consideration of the nanocrystal bandgap, along with the alignment of valence and conduction band energies relative to that of the acceptor, in order to achieve desired output of energy or electron transfer.In this Account, we focus on key aspects of managing energy flow from excited semiconductor nanocrystals to surface-bound chromophores. The singlet and triplet characteristics of the semiconductor nanoparticle enable tuning of energy transfer pathways through bandgap engineering. In addition to the alignment of energy levels between the semiconductor donor and the singlet/triplet energy levels of the acceptor dye, other parameters such as spectral overlap, surface binding through functional groups, and rate of competing energy transfer pathways all play integral roles in directing energy transfer. For example, in a prototypical halide perovskite nanocrystal-rhodamine dye assembly, singlet energy transfer is observed when the donor is a high-bandgap semiconductor (e.g., CsPbBr3, Eg= 2.47 eV). However, when the donor is a low-bandgap semiconductor (e.g., CsPbI3, Eg = 1.87 eV), one observes only triplet energy transfer. Tuning of the donor bandgap with mixed halide perovskites (e.g., CsPb(BrxI1-x)3) allows for populations of both singlet and triplet excited states of the acceptor dye. Additionally, triplet characteristics of the donor semiconductor nanocrystal can be further enhanced through Mn doping which places low-energy triplet-active states within the nanocrystal donor.The ability to steer energy transfer pathways in a semiconductor nanocrystal-dye assembly finds its use in the design of semiconductor-multichromophoric films. Such hybrid films can down-shift or up-convert incident photons and deliver emission at desired wavelengths. By selecting high energy donor (e.g., CsPbBr3) one can down-shift the incident photons through energy transfer cascade, as in the case of the CsPbBr3-rubrene-tetraphenyldibenzoperiflanthene (DBP) system to populate singlet excited DBP (perylene derivative). On the other hand, when the donor energy is low as in the case of CsPbI3-rubrene-DBP, one can populate singlet DBP via triplet-triplet annihilation. Thus, by steering energy transfer pathways, it is possible to manage the photon flow and obtain desired emission output. Fundamental understanding of excited state processes responsible for energy transfer will assist in designing light harvesting assemblies that can manage photon delivery effectively in display devices and other optoelectronic devices.

Origin of Dopant-Carrier Exchange Coupling and Excitonic Zeeman Splitting in Mn2+-Doped Lead Halide Perovskite Nanocrystals

Low-dimensional metal halide perovskites have unique optical and electrical properties that render them attractive for the design of diluted magnetic semiconductors. However, the nature of dopant-exciton exchange interactions that result in spin-polarization of host-lattice charge carriers as a basis for spintronics remains unexplored. Here, we investigate Mn2+-doped CsPbCl3 nanocrystals using magnetic circular dichroism spectroscopy and show that Mn2+ dopants induce excitonic Zeeman splitting which is strongly dependent on the nature of the band-edge structure. We demonstrate that the largest splitting corresponds to exchange interactions involving the excited state at the M-point along the spin-orbit split-off conduction band edge. This splitting gives rise to an absorption-like C-term excitonic MCD signal, with the estimated effective g-factor (geff) of ca. 70. The results of this work help resolve the assignment of absorption transitions observed for metal halide perovskite nanocrystals and allow for a design of new diluted magnetic semiconductor materials for spintronics applications.

High-Temperature, Reversible, and Robust Thermochromic Fluorescence Based on Rb2 MnBr4 (H2 O)2 for Anti-Counterfeiting

Thermochromic fluorescent materials (TFMs) characterized by noticeable emission color variation with temperature have attracted pervasive attention for their frontier application in stimulus-response and optical encryption technologies. However, existing TFMs typically suffer from weak PL reversibility as well as limited mild operating temperature and severe temperature PL quenching. PL switching under extreme conditions such as high temperature will undoubtedly improve encryption security, while it is still challenging for present TFMs. In this work, high-temperature thermochromic fluorescence up to 473 K and robust structural and optical reversibility of 80 cycles are observed in Rb2 MnBr4 (H2 O)2 and related crystals, which is seldom reported for PL changes at such a high temperature. Temperature-driven nonluminous, red and green light emission states can be achieved at specific temperatures and the modulation mechanism is verified by in situ optical and structural measurements and single particle transition. By virtue of this unique feature, a multicolor anti-counterfeiting label based on a broad temperature gradient and multidimensional information encryption applications are demonstrated. This work opens a window for the design of inorganic materials with multi-PL change and the development of advanced encryption strategies with extreme stimuli source.

Rapid and Direct Liquid-Phase Synthesis of Luminescent Metal Halide Superlattices

The crystallization of nanocrystal building blocks into artificial superlattices has emerged as an efficient approach for tailoring the nanoscale properties and functionalities of novel devices. To date, ordered arrays of colloidal metal halide nanocrystals have mainly been achieved by using post-synthetic strategies. Here, a rapid and direct liquid-phase synthesis is presented to achieve a highly robust crystallization of luminescent metal halide nanocrystals into perfect face-centered-cubic (FCC) superlattices on the micrometer scale. The continuous growth of individual nanocrystals is observed within the superlattice, followed by the disassembly of the superlattices into individually dispersed nanocrystals owing to the highly repulsive interparticle interactions induced by large nanocrystals. Transmission electron microscopy characterization reveals that owing to an increase in solvent entropy, the structure of the superlattices transforms from FCC to hexagonal close-packed (HCP) and the nanocrystals disassemble. The FCC superlattice exhibits a single and slightly redshifted emission, due to the reabsorption-free property of the building block units. Compared to individual nanocrystals, the superlattices have three times higher quantum yield with improved environmental stability, making them ideal for use as ultrabright blue-light emitters. This study is expected to facilitate the creation of metamaterials with ordered nanocrystal structures and their practical applications.

Recent Developments of Microscopic Study for Lanthanide and Manganese Doped Luminescent Materials

Luminescent materials are indispensable for applications in lighting, displays and photovoltaics, which can transfer, absorb, store and utilize light energy. Their performance is closely related with their size and morphologies, exact atomic arrangement, and local configuration about photofunctional centers. Advanced electron microscopy-based techniques have enabled the possibility to study nanostructures with atomic resolution. Especially, with the advanced micro-electro-mechanical systems, it is able to characterize the luminescent materials at the atomic scale under various environments, providing a deep understanding of the luminescent mechanism. Accordingly, this review summarizes the recent achievements of microscopic study to directly image the microstructure and local environment of activators in lanthanide and manganese (Ln/Mn²⁺ )-doped luminescent materials, including: 1) bulk materials, the typical systems are nitride/oxynitride phosphors; and 2) nanomaterials, such as nanocrystals (hexagonal-phase NaLnF₄ and perovskite) and 2D nanosheets (Ca₂ Ta₃ O₁₀ and MoS₂ ). Finally, the challenges and limitations are highlighted, and some possible solutions to facilitate the developments of advanced luminescent materials are provided.

Engineering the Optical Properties of CsPbBr3 Nanoplatelets through Cd2+ Doping

Lead halide perovskite nanoplatelets (NPls) attract significant attention due to their exceptional and tunable optical properties. Doping is a versatile strategy for modifying and improving the optical properties of colloidal nanostructures. However, the protocols for B-site doping have been rarely reported for 2D perovskite NPls. In this work, we investigated the post-synthetic treatment of CsPbBr₃ NPls with different Cd²⁺ sources. We show that the interplay between Cd²⁺ precursor, NPl concentrations, and ligands determines the kinetics of the doping process. Optimization of the treatment allows for the boosting of linear and nonlinear optical properties of CsPbBr₃ NPls via doping or/and surface passivation. At a moderate doping level, both the photoluminescence quantum yield and two-photon absorption cross section increase dramatically. The developed protocols of post-synthetic treatment with Cd²⁺ facilitate further utilization of perovskite NPls in nonlinear optics, photonics, and lightning.

Large Spectral Shift of Mn2+ Emission Due to the Shrinkage of the Crystalline Host Lattice of the Hexagonal CsCdCl3 Crystals and Phase Transition

All-inorganic halide perovskite crystals are considered excellent optical host lattices for various dopants to obtain wavelength-tunable emissions with ultra-broad bands even over a wide spectral range. Here, a series of Mn²⁺-doped bulk ligand-free CsCdCl₃ (CCC) perovskite crystals with a hexagonal shape and size of about 1 millimeter (mm) have been prepared by a facile hydrothermal method. These CCC:Mn²⁺ (CCC:Mn) crystals emit the representative orange-red photoluminescence (PL) of Mn²⁺ (⁴T₁(G)-⁶A₁(S)) in the centers of hexagonal octahedrons coordinated with six Cl^- ions. A fine-tuning of the Mn²⁺ concentration from 1 to 50 mol % Cd²⁺ induces a substantial red shift of emission spectra from 570 to 630 nm due to the shrinkage of the crystalline host lattice, and the maximum intensity of emission is achieved at 20 mol % Mn²⁺ doping. A further increase in the Mn²⁺ concentration causes a decrease of the PL intensity due to the phase transition from CCC to CsMnCl₃·2H₂O (CMCH). The strong excitation bands at 360, 370, 420, and 440 nm can make the excitation of the emissive CCC:Mn crystals possible with ultraviolet (UV) and blue chips for application in white light-emitting diodes (WLEDs). The similarity of the Mn²⁺-concentration-dependent emission spectra excited by various wavelengths indicates that there is only one type of site for Mn²⁺ occupation in CCC.

Hexamethyldisilazane-Assisted Ambient Condition Mn2+ Doping Perovskite Nanocrystals

Doping Mn2+ ions into lead halide perovskite (LHP) nanocrystals (NCs) has attracted great attention in the optoelectronic fields due to the stability enhancement and unique dual-color emission characteristics arising from...

Interstitial Nature of Mn2+ Doping in 2D Perovskites

Halide perovskites doped with magnetic impurities (such as the transition metals Mn²⁺, Co²⁺, Ni²⁺) are being explored for a wide range of applications beyond photovoltaics, such as spintronic devices, stable light-emitting diodes, single-photon emitters, and magneto-optical devices. However, despite several recent studies, there is no consensus on whether the doped magnetic ions will predominantly replace the octahedral B-site metal via substitution or reside at interstitial defect sites. Here, by performing correlated nanoscale X-ray microscopy, spatially and temporally resolved photoluminescence measurements, and magnetic force microscopy on the inorganic 2D perovskite Cs₂PbI₂Cl₂, we show that doping Mn²⁺ into the structure results in a lattice expansion. The observed lattice expansion contrasts with the predicted contraction expected to arise from the B-site metal substitution, thus implying that Mn²⁺ does not replace the Pb²⁺ sites. Photoluminescence and electron paramagnetic resonance measurements confirm the presence of Mn²⁺ in the lattice, while correlated nano-XRD and X-ray fluorescence track the local strain and chemical composition. Density functional theory calculations predict that Mn²⁺ atoms reside at the interstitial sites between two octahedra in the triangle formed by one Cl^- and two I^- atoms, which results in a locally expanded structure. These measurements show the fate of the transition metal dopants, the local structure, and optical emission when they are doped at dilute concentrations into a wide band gap semiconductor.

CsPbBr3-CdS heterostructure: stabilizing perovskite nanocrystals for photocatalysis

The instability of cesium lead bromide (CsPbBr3) nanocrystals (NCs) in polar solvents has hampered their use in photocatalysis. We have now succeeded in synthesizing CsPbBr3-CdS heterostructures with improved stability and photocatalytic performance. While the CdS deposition provides solvent stability, the parent CsPbBr3 in the heterostructure harvests photons to generate charge carriers. This heterostructure exhibits longer emission lifetime (τ ave = 47 ns) than pristine CsPbBr3 (τ ave = 7 ns), indicating passivation of surface defects. We employed ethyl viologen (EV2+) as a probe molecule to elucidate excited state interactions and interfacial electron transfer of CsPbBr3-CdS NCs in toluene/ethanol mixed solvent. The electron transfer rate constant as obtained from transient absorption spectroscopy was 9.5 × 1010 s-1 and the quantum efficiency of ethyl viologen reduction (Φ EV+˙) was found to be 8.4% under visible light excitation. The Fermi level equilibration between CsPbBr3-CdS and EV2+/EV+˙ redox couple has allowed us to estimate the apparent conduction band energy of the heterostructure as -0.365 V vs. NHE. The insights into effective utilization of perovskite nanocrystals built around a quasi-type II heterostructures pave the way towards effective utilization in photocatalytic reduction and oxidation processes.

Perovskite energy funnels for efficient white emission

Doping Mn²⁺ into CsPbCl₃ nanocrystals (NCs) yields strong orange emission, while the related emission in Mn²⁺ doped CsPbBr₃ NCs is impaired seriously. This is mainly ascribed to back energy transfer from the Mn²⁺ dopant to the host. Doping Mn²⁺ into perovskites with multiple-quantum-well (MQW) structures may address this issue, where the energy funnels ensure a rapid energy transfer process, and thus resulting in a high photoluminescence quantum yield (PLQY). Here, we have developed an Ag⁺ assisted Mn²⁺ doping method in which Mn²⁺ can be easily doped into Br-based MQW perovskites. In this MQW perovskites, both nanoplatelets (NPLs) and NCs were formed simultaneously, where efficient energy transfer occurred from the NPLs with a higher energy bandgap to the NCs with a smaller energy bandgap, and then to the Mn²⁺ dopants. White lighting solution with a PLQY up to 98% has been acquired by altering the experimental parameters, such as reaction time and the Pb-to-Mn feed ratio. The successful doping of Mn²⁺ into CsPbBr₃ host has great significance and shows promising application for next-generation white lighting.

NMR spectroscopy probes microstructure, dynamics and doping of metal halide perovskites

Solid-state magic-angle spinning NMR spectroscopy is a powerful technique to probe atomic-level microstructure and structural dynamics in metal halide perovskites. It can be used to measure dopant incorporation, phase segregation, halide mixing, decomposition pathways, passivation mechanisms, short-range and long-range dynamics, and other local properties. This Review describes practical aspects of recording solid-state NMR data on halide perovskites and how these afford unique insights into new compositions, dopants and passivation agents. We discuss the applicability, feasibility and limitations of ¹H, ¹³C, ¹⁵N, ¹⁴N, ¹³³Cs, ⁸⁷Rb, ³⁹K, ²⁰⁷Pb, ¹¹⁹Sn, ¹¹³Cd, ²⁰⁹Bi, ¹¹⁵In, ¹⁹F and ²H NMR in typical experimental scenarios. We highlight the pivotal complementary role of solid-state mechanosynthesis, which enables highly sensitive NMR studies by providing large quantities of high-purity materials of arbitrary complexity and of chemical shifts calculated using density functional theory. We examine the broader impact of solid-state NMR on materials research and how its evolution over seven decades has benefitted structural studies of contemporary materials such as halide perovskites. Finally, we summarize some of the open questions in perovskite optoelectronics that could be addressed using solid-state NMR. We, thereby, hope to stimulate wider use of this technique in materials and optoelectronics research.

Phase Engineering of Cesium Manganese Bromides Nanocrystals with Color-Tunable Emission

For display applications, it is highly desirable to obtain tunable red/green/blue emission. However, lead-free perovskite nanocrystals (NCs) generally exhibit broadband emission with poor color purity. Herein, we developed a unique phase transition strategy to engineer the emission color of lead-free cesium manganese bromides NCs and we can achieve a tunable red/green/blue emission with high color purity in these NCs. Such phase transition can be triggered by isopropanol: from one dimensional (1D) CsMnBr₃ NCs (red-color emission) to zero dimensional (0D) Cs₃ MnBr₅ NCs (green-color emission). Furthermore, in a humid environment both 1D CsMnBr₃ NCs and 0D Cs₃ MnBr₅ NCs can be transformed into 0D Cs₂ MnBr₄ ⋅2 H₂ O NCs (blue-color emission). Cs₂ MnBr₄ ⋅2 H₂ O NCs could inversely transform into the mixture of CsMnBr₃ and Cs₃ MnBr₅ phase during the thermal annealing dehydration step. Our work highlights the tunable optical properties in single component NCs via phase engineering and provides a new avenue for future endeavors in light-emitting devices.

State of the Art and Prospects for Halide Perovskite Nanocrystals

Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.

Switching on near-infrared light in lanthanide-doped CsPbCl3 perovskite nanocrystals

The accessible emission spectral range of lead halide perovskite (LHP) CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) has remained so far limited to wavelengths below 1 μm, corresponding to the emission line of Yb3+, whereas the direct sensitization of other near-infrared (NIR) emitting lanthanide ions is unviable. Herein, we present a general strategy to enable intense NIR emission from Er3+ at ∼1.5 μm, Ho3+ at ∼1.0 μm and Nd3+ at ∼1.06 μm through a Mn2+-mediated energy-transfer pathway. Steady-state and time-resolved photoluminescence studies show that energy-transfer efficiencies of about 39%, 35% and 70% from Mn2+ to Er3+, Ho3+ and Nd3+ are obtained, leading to photoluminescence quantum yields of ∼0.8%, ∼0.7% and ∼3%, respectively. This work provides guidance on constructing energy-transfer pathways in semiconductors and opens new perspectives for the development of lanthanide-functionalized LHPs as promising materials for optoelectronic devices operating in the NIR region.

A Review on Cs-Based Pb-Free Double Halide Perovskites: From Theoretical and Experimental Studies to Doping and Applications

Despite the progressive enhancement in the flexibility of Pb-based perovskites for optoelectronic applications, regrettably, they are facing two main challenges; (1) instability, which originates from using organic components in the perovskite structure, and (2) toxicity due to Pb. Therefore, new, stable non-toxic perovskite materials are demanded to overcome these drawbacks. The research community has been working on a wide variety of Pb-free perovskites with different molecular formulas and dimensionality. A variety of Pb-free halide double perovskites have been widely explored by different research groups in search for stable, non-toxic double perovskite material. Especially, Cs-based Pb-free halide double perovskite has been in focus recently. Herein, we present a review of theoretical and experimental research on Cs-based Pb-free double halide perovskites of structural formulas Cs2M+M3+X6 (M+ = Ag+, Na+, In+ etc.; M3+= Bi3+, In3+, Sb3+; X = Cl-, Br-, I¯) and Cs2M4+X6 (M4+ = Ti4+, Sn4+, Au4+ etc.). We also present the challenges faced by these perovskite compounds and their current applications especially in photovoltaics alongside the effect of metal dopants on their performance.

Lead-free Mn-doped antimony halide perovskite quantum dots with bright deep-red emission

We reported the first synthesis of Mn2+ doped Cs3Sb2Clx/Br9-x (0 ≤ x ≤ 9) perovskite quantum dots (PQDs) by regulating the coprecipitation of Mn2+ and Sb3+ with thiol ligands. These lead-free PQDs demonstrated bright photoluminescence emission centered at 660 nm and a high quantum yield of ∼49%, making them suitable for optical applications.

Precise Ligand Tuning Emission of Mn-Doped CsPbCl3 Nanocrystals by the Amount of Sulfonates

Using Mn-doped CsPbCl₃ nanocrystals (Mn:CsPbCl₃ NCs) to improve perovskite's properties is becoming an important strategy. Here, we demonstrate a modified supersaturated recrystallization route to synthesize high-quality Mn:CsPbCl₃ NCs at room temperature. Unprecedentedly, sulfonate ligands with various concentrations are shown to successfully tune the dual-color emission of Mn:CsPbCl₃ NCs. Ultrafast transient absorption studies reveal that the host-to-dopant internal energy-transfer process involves the mediated traps. Interestingly, the dual-color emission is tuned via stabilizing mediated traps with a small amount of ligand (band edge (BE) emission reduces and Mn²⁺ emission increases), passivating the deep traps with a large amount of ligand (Mn²⁺ emission increases), and destroying Mn:CsPbCl₃ NCs with too much ligand (both BE and Mn²⁺ emission is quenched). Furthermore, the ligand tuning Mn²⁺ emission exhibits quenching for Cu²⁺ with high sensitivity and selectivity. Our work provides a new strategy to tune the optical properties of Mn:CsPbCl₃ NCs and presents its potential application in an optical detector.

Journey of ZnO quantum dots from undoped to rare-earth and transition metal-doped and their applications

Currently, developments in the field of quantum dots (QDs) have attracted researchers worldwide. A large variety of QDs have been discovered in the few years, which have excellent optoelectronic, antibacterial, magnetic, and other properties. However, ZnO is the single known material that can exist in the quantum state and can hold all the above properties. There is a lot of work going on in this field and we will be shorthanded if we do not accommodate this treasure at one place. This manuscript will prove to be a milestone in this noble cause. Having a tremendous potential, there is a developing enthusiasm toward the application of ZnO QDs in diverse areas. Sol-gel method being the simplest is the widely-favored synthetic method. Synthesis via this method is largely affected by a number of factors such as the reaction temperature, duration of the reaction, type of solvent, pH of the solution, and the precipitating agent. Doping enhances the optical, magnetic, anti-bacterial, anti-microbial, and other properties of ZnO QDs. However, doping elements reside mostly on the surface of the QDs. The presence of doping elements inside the core is still a major challenge for doping techniques. In this review article, we have focused on pure, rare-earth, and transition metal-doped ZnO QD properties, and the various synthetic processes and applications. Quantum confinement effect is present in nearly every aspect of the QDs. The effect of quantum confinement has also been summarized in this manuscript. Furthermore, the doping of rare earth elements and transition metal, synthetic methods for different organic molecule-capped ZnO QDs, mechanisms for reactive oxygen species (ROS) generation, drug delivery system for cancer treatment, and many more application are discussed in this paper.

Synthesis of lead-free Cs4(Cd1-xMnx)Bi2Cl12 (0 ≤ x ≤ 1) layered double perovskite nanocrystals with controlled Mn-Mn coupling interaction

Lead-free perovskites and their analogues have been extensively studied as a class of next-generation luminescent and optoelectronic materials. Herein, we report the synthesis of new colloidal Cs4M(ii)Bi2Cl12 (M(ii) = Cd, Mn) nanocrystals (NCs) with unique luminescence properties. The obtained Cs4M(ii)Bi2Cl12 NCs show a layered double perovskite (LDP) crystal structure with good particle stability. Density functional theory calculations show that both samples exhibit a wide, direct bandgap feature. Remarkably, the strong Mn-Mn coupling effect of the Cs4M(ii)Bi2Cl12 NCs results in an ultra-short Mn photoluminescence (PL) decay lifetime of around 10 μs, around two orders of magnitude faster than commonly observed Mn2+ dopant emission in NCs. Diluting the Mn2+ ion concentration through forming Cs4(Cd1-xMnx)Bi2Cl12 (0 < x < 1) alloyed LDP NCs leads to prolonged PL lifetimes and enhanced PL quantum yields. Our study provides the first synthetic example of Bi-based LDP colloidal NCs with potential for serving as a new category of stable lead-free perovskite-type materials for various applications.

Halide Pb-Free Double–Perovskites: Ternary vs. Quaternary Stoichiometry

In view of their applicability in optoelectronics, we review here the relevant structural, electronic, and optical features of the inorganic Pb-free halide perovskite class. In particular, after discussing the reasons that have motivated their introduction in opposition to their more widely investigated organic-inorganic counterparts, we highlight milestones already achieved in their synthesis and characterization and show how the use of ab initio ground and excited state methods is relevant in predicting their properties and in disclosing yet unsolved issues which characterize both ternary and quaternary stoichiometry double-perovskites.

Modifying the Crystal Field of CsPbCl3:Mn2+ Nanocrystals by Co-doping to Enhance Its Red Emission by a Hundredfold

CsPbCl₃:Mn²⁺ is a practical solution for obtaining red-orange light inorganic perovskite nanocrystals since CsPbI₃ is unstable. Increasing the concentration of Mn²⁺ is an effective way to enhance the orange-red emission of CsPbCl₃:Mn²⁺. However, the relationship between emission intensity of the Mn²⁺ dopant and the concentration of Mn²⁺ is very chaotic in different studies. As a transition metal ion, the electronic states of Mn²⁺ are very sensitive to the crystal field environment. Here, the crystal field of the CsPbCl₃:Mn²⁺ nanocrystals was adjusted by co-doping other cations, and the concentration of Mn²⁺ remained unchanged. Additionally, the crystal field strength of different samples was calculated. Compared with the CsPbCl₃:Mn²⁺ nanocrystals, the red-orange peak in the fluorescence spectrum of CsPbCl₃:Mn²⁺, Er³⁺ nanocrystals was redshifted from 580 to 600 nm and enhanced by 100 times successfully. The same experiment was carried out on CsPbCl₃:Mn²⁺ nanoplatelets at the same time to confirm the changed crystal field around Mn²⁺. The effect of co-doping cations on the luminescence properties of Mn²⁺ is similar to that in nanocubes, and the mechanism was analyzed in detail.

Cation-doping matters in caesium lead halide perovskite nanocrystals: from physicochemical fundamentals to optoelectronic applications

All-inorganic caesium lead halide perovskite nanocrystals (PeNCs) with different dimensionalities have recently fascinated the research community due to their extraordinary optoelectronic properties including tunable bandgaps over the entire visible spectral region, high photoluminescence quantum yields (PLQYs) close to unity and narrow emission line widths down to 10-20 nm, making them particularly suitable as promising candidates for numerous applications ranging from light-emitting diodes (LEDs), solar cells to scintillators. Despite the considerable progress made in the past six years, the real-world applications of caesium lead halide PeNCs themselves especially in the category of CsPbX₃ (X = Cl, Br and I) are still restricted by their labile crystal lattices and downgraded luminescence when exposed to ambient air conditions. Recent experimental and theoretical studies on cation doping have proven to be an effective way to significantly improve the physicochemical properties of cesium lead halide PeNCs, which would have profound implications for a range of applications. In this review, we provide a brief overview of the most recent advances in cation-doped all-inorganic caesium lead halide PeNCs, aimed at developing high-performance and long-term stable optoelectronic and photovoltaic devices, which covers areas from their fundamental considerations of cation doping, controlled synthesis methodology and novel physicochemical properties to the optoelectronic applications with an emphasis on perovskite-based LEDs and solar cells. And finally, some possible directions of future efforts toward this active research field are also proposed.

Modulating Charge-Carrier Dynamics in Mn-Doped All-Inorganic Halide Perovskite Quantum Dots through the Doping-Induced Deep Trap States

Transition-metal ion doping has been demonstrated to be effective for tuning the photoluminescence properties of perovskite quantum dots (QDs). However, it would inevitably introduce defects in the lattice. As the Mn concentration increases, the Mn dopant photoluminescence quantum yield (PLQY) first increases and then decreases. Herein the influence of the dopant and the defect states on the photophysics in Mn-doped CsPbCl₃ QDs was studied by time-resolved spectroscopies, whereas the energy levels of the possible defect states were analyzed by density functional theory calculations. We reveal the formation of deep interstitials defects (Cl_i) by Mn²⁺ doping. The depopulation of initial QD exciton states is a competition between exciton-dopant energy transfer and defect trapping on an early time scale (<100 ps), which determines the final PLQY of the QDs. The present work establishes a robust material optimization guideline for all of the emerging applications where a high PLQY is essential.

Resolving Enhanced Mn2+ Luminescence near the Surface of CsPbCl3 with Time-Resolved Cathodoluminescence Imaging

Mn²⁺ doping of lead halide perovskites has garnered recent interest because it produces stable orange luminescence in tandem with perovskite emission. Here, we observe enhanced Mn²⁺ luminescence at the edges of Mn²⁺-doped CsPbCl₃ perovskite microplates and suggest an explanation for its origin using the high spatiotemporal resolution of time-resolved cathodoluminescence (TRCL) imaging. We reveal two luminescent decay components that we attribute to two different Mn²⁺ populations. While each component appears to be present both near the surface and in the bulk, the origin of the intensity variation stems from a higher proportion of the longer lifetime component near the perovskite surface. We suggest that this higher emission is caused by an increased probability of electron-hole recombination on Mn²⁺ near the perovskite surface due to an increased trap concentration there. This observation suggests that such surface features have yet untapped potential to enhance emissive properties via control of surface-to-volume ratio.

Bright Blue Light Emission of Ni2+ Ion-Doped CsPbClxBr3-x Perovskite Quantum Dots Enabling Efficient Light-Emitting Devices

In recent years, significant advances have been achieved in the red and green perovskite quantum dot (PQD)-based light-emitting diodes (LEDs). However, the performances of the blue perovskite LEDs are still seriously lagging behind that of the green and red counterparts. Herein, we successfully developed Ni²⁺ ion-doped CsPbCl_xBr_3-x PQDs through the room-temperature supersaturated recrystallization synthetic approach. We simultaneously realized the doping of various concentrations of Ni²⁺ cations and modulated the Cl/Br element ratios by introducing different amounts of NiCl₂ solution in the reaction medium. Using the synthetic method, not only the emission wavelength from 508 to 432 nm of Ni²⁺ ion-doped CsPbCl_xBr_3-x QDs was facially adjusted, but also the photoluminescence quantum yield (PLQY) of PQDs was greatly improved due to efficient removal of the defects of the PQDs. Thus, the blue emission at 470 nm with PLQY of 89% was achieved in 2.5% Ni²⁺ ion-doped CsPbCl_0.99Br_2.01 QDs, which increased nearly three times over that of undoped CsPbClBr₂ QDs and was the highest for the CsPbX₃ PQDs with blue emission, fulfilling the National Television System Committee standards. Benefiting from the highly luminous Ni²⁺ ion-doped PQDs, the blue-emitting LED at 470 nm was obtained, exhibiting an external quantum efficiency of 2.4% and a maximum luminance of 612 cd/m², which surpassed the best performance reported previously for the corresponding blue-emitting PQD-based LED.

Doping and ion substitution in colloidal metal halide perovskite nanocrystals

The past decade has witnessed tremendous advances in synthesis of metal halide perovskites and their use for a rich variety of optoelectronics applications. Metal halide perovskite has the general formula ABX3, where A is a monovalent cation (which can be either organic (e.g., CH3NH3+ (MA), CH(NH2)2+ (FA)) or inorganic (e.g., Cs+)), B is a divalent metal cation (usually Pb2+), and X is a halogen anion (Cl-, Br-, I-). Particularly, the photoluminescence (PL) properties of metal halide perovskites have garnered much attention due to the recent rapid development of perovskite nanocrystals. The introduction of capping ligands enables the synthesis of colloidal perovskite nanocrystals which offer new insight into dimension-dependent physical properties compared to their bulk counterparts. It is notable that doping and ion substitution represent effective strategies for tailoring the optoelectronic properties (e.g., absorption band gap, PL emission, and quantum yield (QY)) and stabilities of perovskite nanocrystals. The doping and ion substitution processes can be performed during or after the synthesis of colloidal nanocrystals by incorporating new A', B', or X' site ions into the A, B, or X sites of ABX3 perovskites. Interestingly, both isovalent and heterovalent doping and ion substitution can be conducted on colloidal perovskite nanocrystals. In this review, the general background of perovskite nanocrystals synthesis is first introduced. The effects of A-site, B-site, and X-site ionic doping and substitution on the optoelectronic properties and stabilities of colloidal metal halide perovskite nanocrystals are then detailed. Finally, possible applications and future research directions of doped and ion-substituted colloidal perovskite nanocrystals are also discussed.

Solvothermal synthesis of Mn-doped CsPbCl3 perovskite nanocrystals with tunable morphology and their size-dependent optical properties

Doping metal ions in inorganic halide perovskite (CsPbX3, X = Cl, Br, I) nanocrystals (NCs) endows the NCs with unique optical characteristics, and has thus attracted immense attention. However, controllable synthesis of high-quality doped perovskite NCs with tunable morphology still remains challenging. Here, we report a facile, effective and unified strategy for the controllable synthesis of Mn-doped CsPbCl3 quantum dots (QDs) and nanoplatelets (NPLs) via a single-step solvothermal method. The incorporation of Mn2+ into CsPbCl3 NCs introduces new broad photoluminescence (PL) emission from Mn2+ while maintaining the structure of host CsPbCl3 NCs nearly intact. The PL intensity, emission peak position and size of the NCs can be accurately adjusted by altering the experimental parameters such as Mn-to-Pb feed ratio and reaction time. Especially, by changing the amount of ligands, Mn-doped CsPbCl3 QDs, NPLs or their mixtures can be obtained. Both of the Mn-doped QDs and NPLs exhibit a size-dependent quantum confinement effect, which is confirmed by the relationship between the size of NCs and the exciton emission peaks. The solvothermal reaction condition plays an important role for the precise control of the structure, morphology and PL properties of the Mn-doped NCs. The as-prepared Mn-doped CsPbCl3 NPLs with thickness down to ∼2 nm exhibit a PL quantum yield (PLQY) of more than 22%. This work introduces a new strategy for the controllable synthesis of Mn-doped perovskite NCs, which provides ideas for the in-depth study of the dope-and-grow process and can be extended to approaches of doping other metal ions.

Advances in the Stability of Halide Perovskite Nanocrystals

Colloidal halide perovskite nanocrystals are promising candidates for next-generation optoelectronics because of their facile synthesis and their outstanding and size-tunable properties. However, these materials suffer from rapid degradation, similarly to their bulk perovskite counterparts. Here, we survey the most recent strategies to boost perovskite nanocrystals stability, with a special focus on the intrinsic chemical- and compositional-factors at synthetic and post-synthetic stage. Finally, we review the most promising approaches to address the environmental extrinsic stability of perovskite nanocrystals (PNCs). Our final goal is to outline the most promising research directions to enhance PNCs' lifetime, bringing them a step closer to their commercialization.

Coupled Halide-deficient and Halide-rich Reaction System for Doping in Perovskite Armed Nanostructures

Insights of Mn(II) doping in CsPbCl₃-armed hexapod nanostructures is reported. These complex structures were typically formed in halide concentration tuned modulated reactions. Cores were first formed under halide deficient condition and with enriching halides; these were transformed to armed structures. Doping of Mn(II) was observed facilitated during the arm growth in the second stage of the reaction. These observations were supported with decoupled reactions with minimized and maximized halide concentrations carried out in separate reactions. However, less interference for the exciton to dopant energy transfer was noticed for the defect states created in halide-deficient medium, and the intensity of the dopant emission remained proportional to the amount of dopant inserted in the nanocrystals. Being this is an in situ observation in the coupled reactions of both poor and rich halide reaction systems, the finding would strengthen the understanding of doping in perovskite host nanocrystals.

Perovskite quantum dots for light-emitting devices

Perovskite quantum dots (QDs) have been hotly pursued in recent decades owing to their quantum confinement effect and defect-tolerant nature. Their unique optical properties, such as high photoluminescence quantum yield (PLQY) approaching unity, narrow emission bandwidth, tunable wavelength spanning the entire visible spectrum, and compatibility with flexible/stretchable electronics, render perovskite QDs promising for next-generation solid lighting sources and information displays. Herein, the advances in perovskite QDs and their applications in LEDs are reviewed. Strategies to fabricate efficient perovskite QDs and device configuration, including material composition design, synthetic methods, surface engineering, and device optimization, are investigated and highlighted. Moreover, the main challenges in perovskite QDs of instability and toxicity (lead-based) are identified, while the solutions undertaken with respect to composition engineering, device encapsulation, and lead-replacement QDs are demonstrated. Meanwhile, perspectives for the further development of perovskite QDs and corresponding LEDs are presented.

Energetic hot electrons from exciton-to-hot electron upconversion in Mn-doped semiconductor nanocrystals

Generation of hot electrons and their utilization in photoinduced chemical processes have been the subjects of intense research in recent years mostly exploring hot electrons in plasmonic metal nanostructures created via decay of optically excited plasmon. Here, we present recent progress made in generation and utilization of a different type of hot electrons produced via biphotonic exciton-to-hot electron "upconversion" in Mn-doped semiconductor nanocrystals. Compared to the plasmonic hot electrons, those produced via biphotonic upconversion in Mn-doped semiconductor nanocrystals possess much higher energy, enabling more efficient long-range electron transfer across the high energy barrier. They can even be ejected above the vacuum level creating photoelectrons, which can possibly produce solvated electrons. Despite the biphotonic nature of the upconversion process, hot electrons can be generated with weak cw excitation equivalent to the concentrated solar radiation without requiring intense or high-energy photons. This perspective reviews recent work elucidating the mechanism of generating energetic hot electrons in Mn-doped semiconductor nanocrystals, detection of these hot electrons as photocurrent or photoelectron emission, and their utilization in chemical processes such as photocatalysis. New opportunities that the energetic hot electrons can open by creating solvated electrons, which can be viewed as the longer-lived and mobile version of hot electrons more useful for chemical processes, and the challenges in practical utilization of energetic hot electrons are also discussed.

Improved Doping and Emission Efficiencies of Mn-Doped CsPbCl3 Perovskite Nanocrystals via Nickel Chloride

It is challenging to improve the emission efficiency of Mn-doped CsPbCl₃ (Mn:CsPbCl₃) nanocrystals (NCs) because the excellent optical performances are dependent on high doping efficiency and few defects and traps. Steady-state and time-resolved photoluminescence (PL) spectroscopies were used to investigate the luminescence properties of Mn:CsPbCl₃ NCs with different Mn doping levels synthesized in the presence of nickel chloride. The doping efficiency of Mn ions in Mn:CsPbCl₃ NCs was greatly enhanced in the presence of NiCl₂, and the PL wavelength of Mn²⁺ ions was tuned from 594 to 638 nm by varying the concentration of dopant Mn from 0.11% to 15.25%. The high emission quantum yields of Mn:CsPbCl₃ NCs with orange and red emissions peaked at 600 and 620 nm in hexane were 70% and 39%, respectively. The improvement in doping and emission efficiencies of Mn²⁺ was attributed to the enhanced formation energies of the Mn doping under the Mn and Ni codoped configuration and the resulting reduction of defects and traps in Mn:CsPbCl₃ NCs with incorporation of Ni²⁺ ions.

From Nonluminescent to Blue-Emitting Cs4 PbBr6 Nanocrystals: Tailoring the Insulator Bandgap of 0D Perovskite through Sn Cation Doping

All-inorganic cesium lead halide perovskite nanocrystals (NCs) with different dimensionalities have recently fascinated the research community due to their extraordinary optoelectronic performance such as tunable bandgaps over the entire visible spectral region. However, compared to well-developed 3D CsPbX₃ perovskites (X = Cl, Br, and I), the bandgap tuning in 0D Cs₄ PbX₆ perovskite NCs remains an arduous task. Herein, a simple but valid strategy is proposed to tailor the insulator bandgap (≈3.96 eV) of Cs₄ PbBr₆ NCs to the blue spectral region by changing the local coordination environment of isolated [PbBr₆ ]^4- octahedra in the Cs₄ PbBr₆ crystal through Sn cation doping. Benefitting from the unique Pb²⁺ -poor and Br^- -rich reaction environment, the Sn cation is successfully introduced into the Cs₄ PbBr₆ NCs, forming coexisting point defects comprising substitutional Sn_Pb and interstitial Br_i , thereby endowing these theoretically nonluminescent Cs₄ PbBr₆ NCs with an ultranarrow blue emission at ≈437 nm (full width at half maximum, ≈12 nm). By combining the experimental results with first-principles calculations, an unusual electronic dual-bandgap structure, comprising the newly emerged semiconducting bandgap of ≈2.87 eV and original insulator bandgap of ≈3.96 eV, is found to be the underlying fundamental reason for the ultranarrow blue emission.

Reducing Defects in Halide Perovskite Nanocrystals for Light-Emitting Applications

The large specific surface area of perovskite nanocrystals (NCs) increases the likelihood of surface defects compared to that of bulk single crystals and polycrystalline thin films. It is thus crucial to comprehend and control their defect population in order to exploit the potential of perovskite NCs. This Perspective describes and classifies recent advances in understanding defect chemistry and avenues toward defect density reduction in perovskite NCs, and it does so in the context of the promise perceived in light-emitting devices. Several pathways for decreasing the defect density are explored, including advanced NC syntheses, new surface-capping strategies, doping with metal ions and rare earths, engineering elemental compensation, and the translation of core-shell heterostructures into the perovskite materials family. We close with challenges that remain in perovskite NC defect research.

Yb- and Mn-Doped Lead-Free Double Perovskite Cs2AgBiX6 (X = Cl-, Br-) Nanocrystals

Lead-free double perovskite nanocrystals (NCs) have emerged as a new category of materials that hold the potential for overcoming the instability and toxicity issues of lead-based counterparts. Doping chemistry represents a unique avenue toward tuning and optimizing the intrinsic optical and electronic properties of semiconductor materials. In this study, we report the first example of doping Yb³⁺ ions into lead-free double perovskite Cs₂AgBiX₆ (X = Cl^-, Br^-) NCs via a hot injection method. The doping of Yb³⁺ endows the double perovskite NCs with a newly emerged near-infrared emission band (sensitized from the NC hosts) in addition to their intrinsic trap-related visible photoluminescence. By controlling the Yb-doping concentration, the dual emission profiles and photon relaxation dynamics of the double perovskite NCs can be systematically tuned. Furthermore, we have successfully inserted divalent Mn²⁺ ions in Cs₂AgBiCl₆ NCs and observed emergence of dopant emission. Our work illustrates an effective and facile route toward modifying and optimizing optical properties of double perovskite Cs₂AgBiX₆ (X = Cl^-, Br^-) NCs with an indirect bandgap nature, which can broaden a range of their potential applications in optoelectronic devices.

Insights of Doping and the Photoluminescence Properties of Mn-Doped Perovskite Nanocrystals

Doping Mn²⁺ in semiconductor nanocrystals is widely known for its long-lifetime Mn d-d orange emission. While this had been extensively studied for chalcogenide nanostructures, recently this was also extended to perovskite nanocrystals. Being that CsPbCl₃ has a wide bandgap, the exciton energy transfer was found to be more efficient, but the dopant-induced photoluminescence was also obtained for layered perovskites and quantum-confined CsPbBr₃ nanocrystals. In recent years significant advances have been achieved in understanding the physical insights of doping following various approaches and optimizing the conditions for obtaining intense dopant emission. In addition, several new properties associated with these doped nanocrystals were also reported, and by modulating the compositions, the host bandgap and the dopant emission positions were also tuned. Keeping all of these developments in mind, this Perspective focuses on the insights of doping and the photoluminescence properties of Mn²⁺-doped perovskite nanocrystals. In addition, it also proposes possible future prospects of both synthesis and optical properties of these nanomaterials.

Photoinduced Mn doping in cesium lead halide perovskite nanocrystals

We report the photoinduced post-synthesis method of Mn doping in colloidal perovskite nanocrystals, which can produce Mn-doped CsPbX3 (X = Cl, Br) nanocrystals with preserved size and anisotropic morphology. Photoinduced Mn doping occurs through cation exchange driven by the facile photoinduced halide exchange in dihalomethane (CH2X2, X = Cl, Br) solvent taking advantage of in situ photogeneration of halide ions from the solvent molecules. In the presence of a small amount of Mn acetate dissolved in solvent at sub-micromolar concentration, photoexcitation of the nanocrystals above the bandgap initiates the simultaneous anion and cation exchange. Under the condition of self-anion exchange, the resulting product is only the cation (Mn) doping in the nanocrystal host without changing halide composition, where the extent of doping can be controlled by excitation light intensity. The mild nature of the photoinduced doping also preserves the anisotropic morphology of the nanocrystals. The photoinduced Mn-doping method could be further expanded to other cations providing a versatile means of creating various cation-doped perovskite nanocrystals that are difficult to produce by other means.

Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications, and Their Optical Properties

Metal halide perovskites represent a flourishing area of research, which is driven by both their potential application in photovoltaics and optoelectronics and by the fundamental science behind their unique optoelectronic properties. The emergence of new colloidal methods for the synthesis of halide perovskite nanocrystals, as well as the interesting characteristics of this new type of material, has attracted the attention of many researchers. This review aims to provide an up-to-date survey of this fast-moving field and will mainly focus on the different colloidal synthesis approaches that have been developed. We will examine the chemistry and the capability of different colloidal synthetic routes with regard to controlling the shape, size, and optical properties of the resulting nanocrystals. We will also provide an up-to-date overview of their postsynthesis transformations, and summarize the various solution processes that are aimed at fabricating halide perovskite-based nanocomposites. Furthermore, we will review the fundamental optical properties of halide perovskite nanocrystals by focusing on their linear optical properties, on the effects of quantum confinement, and on the current knowledge of their exciton binding energies. We will also discuss the emergence of nonlinear phenomena such as multiphoton absorption, biexcitons, and carrier multiplication. Finally, we will discuss open questions and possible future directions.

Anion Exchange and the Quantum-Cutting Energy Threshold in Ytterbium-Doped CsPb(Cl1- xBr x)3 Perovskite Nanocrystals

Colloidal halide perovskite nanocrystals of CsPbCl₃ doped with Yb³⁺ have demonstrated remarkably high sensitized photoluminescence quantum yields (PLQYs), approaching 200%, attributed to a picosecond quantum-cutting process in which one photon absorbed by the nanocrystal generates two photons emitted by the Yb³⁺ dopants. This quantum-cutting process is thought to involve a charge-neutral defect cluster within the nanocrystal's internal volume. We demonstrate that Yb³⁺-doped CsPbCl₃ nanocrystals can be converted postsynthetically to Yb³⁺-doped CsPb(Cl_{1- x}Br _x)₃ nanocrystals without compromising the desired high PLQYs. Nanocrystal energy gaps can be tuned continuously from E_g ≈ 3.06 eV (405 nm) in CsPbCl₃ down to E_g ≈ 2.53 eV (∼490 nm) in CsPb(Cl_0.25Br_0.75)₃ while retaining a constant PLQY above 100%. Reducing E_g further causes a rapid drop in PLQY, interpreted as reflecting an energy threshold for quantum cutting at approximately twice the energy of the Yb³⁺²F_7/2 → ²F_5/2 absorption threshold. These data demonstrate that very high quantum-cutting energy efficiencies can be achieved in Yb³⁺-doped CsPb(Cl_{1- x}Br _x)₃ nanocrystals, offering the possibility to circumvent thermalization losses in conventional solar technologies. The presence of water during anion exchange is found to have a deleterious effect on the Yb³⁺ PLQYs but does not affect the nanocrystal shapes or morphologies, or even reduce the excitonic PLQYs of analogous undoped CsPb(Cl_{1- x}Br _x)₃ nanocrystals. These results provide valuable information relevant to the development and application of these unique materials for spectral-shifting solar energy conversion technologies.

Long-Lived Dark Exciton Emission in Mn-Doped CsPbCl3 Perovskite Nanocrystals

The unusual temperature dependence of exciton emission decay in CsPbX₃ perovskite nanocrystals (NCs) attracts considerable attention. Upon cooling, extremely short (sub-ns) lifetimes were observed and were explained by an inverted bright-dark state splitting. Here, we report temperature-dependent exciton lifetimes for CsPbCl₃ NCs doped with 0-41% Mn²⁺. The exciton emission lifetime increases upon cooling from 300 to 75 K. Upon further cooling, a strong and fast sub-ns decay component develops. However, the decay is strongly biexponential and also a weak, slow decay component is observed with a ∼40-50 ns lifetime below 20 K. The slow component has a ∼5-10 times stronger relative intensity in Mn-doped NCs compared to that in undoped CsPbCl₃ NCs. The temperature dependence of the slow component resembles that of CdSe and PbSe quantum dots with an activation energy of ∼19 meV for the dark-bright state splitting. Based on our observations, we propose an alternative explanation for the short, sub-ns exciton decay time in CsPbX₃ NCs. Slow bright-dark state relaxation at cryogenic temperatures gives rise to almost exclusively bright state emission. Incorporation of Mn²⁺ or high magnetic fields enhances the bright-dark state relaxation and allows for the observation of the long-lived dark state emission at cryogenic temperatures.

An overview on enhancing the stability of lead halide perovskite quantum dots and their applications in phosphor-converted LEDs

Beyond the unprecedented success achieved in photovoltaics (PVs), lead halide perovskites (LHPs) have shown great potential in other optoelectronic devices. Among them, nanometer-scale perovskite quantum dots (PQDs) with fascinating optical properties including high brightness, tunable emission wavelength, high color purity, and high defect tolerance have been regarded as promising alternative down-conversion materials in phosphor-converted light-emitting diodes (pc-LEDs) for lighting and next-generation of display technology. Despite the promising applications of perovskite materials in various fields, they have received strong criticism for the lack of stability. The poor stability has also attracted much attention. Within a few years, numerous strategies towards enhancing the stability have been developed. This review summarizes the mechanisms of intrinsic- and extrinsic-environment-induced decomposition of PQDs. Simultaneously, the strategies for improving the stability of PQDs are reviewed in detail, which can be classified into four types: (1) compositional engineering; (2) surface engineering; (3) matrix encapsulation; (4) device encapsulation. Finally, the challenges for applying PQDs in pc-LEDs are highlighted, and some possible solutions to improve the stability of PQDs together with suggestions for further improving the performance of pc-LEDs as well as the device lifetime are provided.

Room temperature synthesis of Mn-doped Cs3Pb6.48Cl16 perovskite nanocrystals with pure dopant emission and temperature-dependent photoluminescence

We report Mn-doped Cs₃Pb_6.48Cl₁₆ nanocrystals with pure dopant emission synthesized at room temperature.