Experimental Determination of the Molar Absorption Coefficient of Cesium Lead Halide Perovskite Quantum Dots

Ni doping in CsPbCl3 nanocrystals: the key to enhanced photoluminescence

This study presents a generic method to selectively enhance radiative pathways over non-radiative states by leveraging vibrational coupling between the host lattice and mid-gap states of doped transition metal ions. While previously demonstrated with Mn, this work successfully incorporates Ni2+ ions into CsPbCl3 perovskite nanocrystals (NCs), showcasing the method's versatility and tunability for radiative decay rates. Structural analyses confirm Ni2+ integration, while temperature-dependent photoluminescence studies reveal that Ni-induced shallow trap states enable vibrational coupling, facilitating charge carrier back-transfer to excitonic states. At 2% doping, this mechanism optimally enhances radiative recombination, achieving room-temperature vibrationally assisted delayed fluorescence (VADF). Förster resonance energy transfer (FRET) experiments further validate the improved radiative efficiency. This work establishes transition metal doping as a transformative and selective strategy for tuning optical properties, paving the way for advancements in energy-efficient technologies such as light-emitting diodes, lasers, and photovoltaics.

Colloidal Perovskite Nanocrystals for Blue-Light-Emitting Diodes and Displays

The evolution of display technology toward ultrahigh resolution, high color purity, and cost-effectiveness has generated interest in metal halide perovskites, particularly colloidal perovskite nanocrystals (PeNCs). PeNCs exhibit narrow emission spectra, high photoluminescence quantum yields, and wide color gamuts, rendering them promising candidates for next-generation displays. Despite significant advancements in perovskite light-emitting diode (PeLED) technology, challenges remain regarding the efficiencies of PeNC-based blue LEDs. Addressing these challenges, including both inherent and external instabilities of PeNCs and operational instabilities of the devices, is important as they collectively impede the broader acceptance and utilization of PeNCs. Herein, a comprehensive overview of the syntheses of dimension- and composition-controlled blue colloidal PeNCs and critical factors influencing the performances of colloidal PeNC-based blue LEDs is provided. Moreover, the advancements of colloidal PeNC-based blue LEDs and challenges associated with the application of these LEDs are explored, and the potentials of these LEDs for application in next-generation displays are emphasized. This review highlights the path forward for the future development of PeNC-based blue LEDs.

Hybrid halide perovskite quantum dots for optoelectronics applications: recent progress and perspective

Nanotechnology has transformed optoelectronics through quantum dots (QDs), particularly metal halide perovskite QDs (PQDs). PQDs boast high photoluminescent quantum yield, tunable emission, and excellent defect tolerance without extensive passivation. Quantum confinement effects, which refer to the phenomenon where the motion of charge carriers is restricted to a small region, produce discrete energy levels and blue shifts in these materials. They are ideal for next-generation optoelectronic devices prized for superior optical properties, low cost, and straightforward synthesis. In this review, along with the fundamental physics behind the phenomenon, we have covered advances in synthesis methods such as hot injection, ligand-assisted reprecipitation, ultrasonication, solvothermal, and microwave-assisted that enable precise control over size, shape, and stability, enhancing their suitability for LEDs, lasers, and photodetectors. Challenges include lead toxicity and cost, necessitating research into alternative materials and scalable manufacturing. Furthermore, strategies like doping and surface passivation that improve stability and emission control are discussed comprehensively, and how lead halide perovskites like CsPbBr3undergo phase transitions with temperature, impacting device performance, are also investigated. We have explored various characterization techniques, providing insights into nanocrystal properties and behaviors in our study. This review highlights PQDs' synthesis, physical and optoelectronic properties, and potential applications across diverse technologies.

Photon Reabsorption and Surface Plasmon Modulating Exciton-to-Dopant Energy Transfer Dynamics in Mn:CsPb(BrCl)3 Quantum Dots

Exciton-to-dopant energy transfer (ET) dynamics of Mn:CsPbX3 quantum dots (QDs), which is dominated by diverse physical factors, requires more comprehensive understanding. Here, the concentration-dependent photon reabsorption effect on ET dynamics has been meticulously analyzed in colloidal Mn:CsPb(BrCl)3 QDs. The results indicate that the photons emitted by the smaller QDs are absorbed by the larger QDs, effectively providing additional excitation light to the latter. The reabsorbed photons play a crucial role in significantly enhancing the ET process in the larger QDs. Additionally, the Mn:CsPb(BrCl)3 QDs/Poly(methyl methacrylate)/Ag/SiO2 multilayer films were fabricated to study the influence of the surface plasmon (SP) on ET dynamics. The results reveal that resonant energy transfer between excitons and SP via dipole interactions can regulate the ET process and Mn2+ emission intensity by controlling the distance between the SP and excitons. These findings provide insights into Mn:CsPbX3 QD ET dynamics and potential methods for controlling their luminescence performance in practical applications.

Probing the cw-Laser-Induced Fluorescence Enhancement in CsPbBr3 Nanocrystal Thin Films: An Interplay between Photo and Thermal Activation

Perovskite nanocrystals hold significant promise for a wide range of applications, including solar cells, LEDs, photocatalysts, humidity and temperature sensors, memory devices, and low-cost photodetectors. Such technological potential stems from their exceptional quantum efficiency and charge carrier conduction capability. Nevertheless, the underlying mechanisms of photoexcitation, such as phase segregation, annealing, and ionic diffusion, remain insufficiently understood. In this context, we harnessed hyperspectral fluorescence microspectroscopy to advance our comprehension of fluorescence enhancement triggered by UV continuous-wave (cw) laser irradiation of CsPbBr3 colloidal nanocrystal thin films. Initially, we explored the kinetics of fluorescence enhancement and observed that its efficiency (φph) correlates with the laser power (P), following the relationship φph = 7.7⟨P⟩0.47±0.02. Subsequently, we estimated the local temperature induced by the laser, utilizing the finite-difference method framework, and calculated the activation energy (Ea) required for fluorescence enhancement to occur. Our findings revealed a very low activation energy, Ea ∼ 9 kJ/mol. Moreover, we mapped the fluorescence photoenhancement by spatial scanning and real-time static mode to determine its microscale length. Below a laser power of 60 μW, the photothermal diffusion length exhibited nearly constant values of approximately (22 ± 5) μm, while a significant increase was observed at higher laser power levels. These results were ascribed to the formation of nanocrystal superclusters within the film, which involves the interparticle spacing reduction, creating the so-called quantum dot solid configuration along with laser-induced annealing for higher laser powers.

Laser-Driven Insulator-Metal Phase Transitions in CsPbI3 Quantum Dots and Influence of Doped Metal Nanowires

All-inorganic CsPbI3 perovskite quantum dots (QDs) have received extensive attention in developing optoelectronic devices due to their outstanding properties. Here, using time-dependent density functional theory (TDDFT), the optical properties of the three distinct phases (α, γ, and δ) of the CsPbI3 QDs are investigated. Surprisingly, the δ phase structured QDs exhibit stronger optical absorption properties than the α and γ phase QDs when exposed to equivalent laser irradiation. Considering the quantum size effect, size regulation is also performed on the three structures, the results reveal a significant improvement in optical properties as the size increases in the direction of laser irradiation. More interestingly, Ag-hybrid QDs show better optical gain and maintain a laser-driven metallic state. Our results demonstrate the great potential of size adjustment and metal nanowire coupling in improving the optoelectronic properties of QDs and developing efficient photovoltaic devices.

Thermodynamics of nanocrystal–ligand binding through isothermal titration calorimetry

Manipulations of nanocrystal (NC) surfaces have propelled the applications of colloidal NCs across various fields such as bioimaging, catalysis, electronics, and sensing applications.