Ultra-High-Sensitive Temperature Sensing Based on Er3+ and Yb3+ Co-Doped Lead-Free Double Perovskite Microcrystals

Broad-Temperature Optical Thermometry via Dual Sensitivity of Self-Trapped Excitons Lifetime and Higher-Order Phonon Anharmonicity in Lead-Free Perovskites

Broad-temperature optical thermometry necessitates materials with exceptional sensitivity and stability across varied thermal conditions, presenting challenges for conventional systems. Here, we report a lead-free, vacancy-ordered perovskite Cs2TeCl6, that achieves precise temperature sensing through a novel combination of self-trapped excitons (STEs) photoluminescence (PL) lifetime modulation and unprecedented fifth-order phonon anharmonicity. The STEs PL lifetime demonstrates a highly temperature-sensitive response from 200 to 300 K, ideal for low-to-intermediate thermal sensing. In contrast, the Eg phonon mode undergoes significant linewidth broadening due to five-phonon scattering processes, with a distinct nonlinear temperature dependence up to 500 K. This fifth-order anharmonic effect enhances Raman-based temperature sensitivity, yielding a specific sensitivity (Sr) of 0.577 % K-1 at 330 K and remaining above 0.5 % K-1 at elevated temperatures. This study presents the first evidence of fifth-order anharmonic effects enhancing Raman-based temperature sensitivity, establishing Cs2TeCl6 as a versatile candidate for broad-temperature optical thermometry and opening new avenues for precise non-contact temperature sensing in advanced technological applications.

Constructing a Self-Referenced NIR-II Thermometer with Energy Tuning of Coordinating Water Molecules by a Minimalist Method

Fluorescence thermometry based on metal halide perovskites is increasingly becoming a hotspot due to its advantages of high detection sensitivity, noninvasiveness, and fast response time. However, it still presents certain technical challenges in practical applications, such as complex synthesis methods, the use of toxic solvents, and being currently mainly based on the visible/first near-infrared light with poor penetration and severe autofluorescence. In this study, we synthesize the second near-infrared (NIR-II) luminescent crystals based on Yb3+/Nd3+-doped zero-dimensional Cs2ScCl5·H2O by a simple "dissolve-dry" method. The whole synthesized process does not involve high temperatures or high pressures. Cs2ScCl5·H2O/Yb3+,Nd3+ has an optimum fluorescence performance when the Yb3+/Nd3+ doping amount is 15%/20%. The emission intensity ratio attributed to Yb3+ and Nd3+ varies with temperature, and this variation is exacerbated due to the fact that the 2F5/2 energy level of Yb3+ can be effectively aligned with the O-H bond stretching vibration energy of coordinating water molecules to facilitate energy transfer. Ultimately, the crystals can act as self-referenced ratiometric NIR-II luminescent thermometers with a maximum relative sensitivity of 1.66% K-1 at 323 K. This work highlights the advantages of NIR-II luminescent materials for temperature sensing, which is significant for advancement in the field of noncontact thermometers.

Laser Characteristics of Er3+/Yb3+:K-BaF2-Al-Phosphate Glasses

Er3+ and Er3+/Yb3+-doped phosphate-based glasses have been synthesized by melt quenching technique and are characterized by absorption spectra, infrared emission, decay curves, Fourier transform infrared spectrum and up-conversion studies. From the absorption spectra, intensity parameters and radiative properties have been derived utilizing the Judd-Ofelt theory. Er3+-doped glass is found to have larger radiative lifetime for the laser originating from 4I13/2 level at 1537 nm. Infrared and visible characteristic emissions have been measured by exciting at 790 nm through down- and up-conversion, respectively. The up-conversion spectra consist of intense green emission at around 525 and 545 nm ascribed to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions, respectively, and a weak red emission at around 656 nm due to the 4F9/2 → 4I15/2 transition of Er3+ ions. Various spectroscopic and laser characteristics of these glasses have been calculated and compared with those of similar reported ones.

Modeling of a Single-Band-Ratiometric Sensor Based on Lattice Positive Thermal Expansion in Eu3+-Activated Halide Perovskite Cs2NaEuCl6

Recently, single-band ratiometric (SBR) thermometry has emerged as an innovative approach to traditional fluorescence thermometry, overcoming uncertainties associated with emission spectrum overlap or scattering while maintaining high spatial resolution and remote monitoring. This paper presents a novel Cs2NaEuCl6 perovskite prepared through a slow-cooling solution method. Additionally, it proposes a temperature sensor model that relies on the thermal quenching of charge-transfer state absorption. Mechanical studies highlight the role of lattice positive thermal expansion in affecting Eu3+ emission. Conversely, a significant emission enhancement is observed upon excitation corresponding to both the ground state and excited state absorption. The distinct luminescent behavior of this Eu3+-activated halide perovskite model makes it suitable for developing a highly sensitive SBR-type sensor with a relative sensitivity (Sr) exceeding 1.5% K-1 and temperature resolution (𝛿T) below 1 K at room temperature. Furthermore, it demonstrates the thermal stability during multiple heating-cooling cycles. Finally, the practical applicability of the proposed SBR model is demonstrated by employing a self-manufactured film sensor that enables precise real-time temperature detection for electronic components. The work is regarded as a significant stride toward the development of cutting-edge and exquisitely sensitive thermometers based on lanthanide-based halide double perovskites.

Study of half-metallic ferromagnetism and transport characteristics of double perovskites Sr2AIrO6 (A = Y, Lu, Sc) for spintronic applications

The precise manipulation of electromagnetic and thermoelectric characteristics in the miniaturization of electronic devices offers a promising foundation for practical applications in quantum computing. Double perovskites characterized by stability, non-toxicity, and spin polarization, have emerged as appealing candidates for spintronic applications. This study explores the theoretical elucidation of the influence of iridium's 5d electrons on the magnetic characteristics of Sr2AIrO6 (A = Y, Lu, Sc) with WIEN2k code. The determined formation energies confirm the thermodynamic stability while an analysis of band structure and the density of states (DOS) reveals a half-metallic ferromagnetic character. This characteristic is comprehensible through the analysis of exchange constants and exchange energies. The current analysis suggests that crystal field effects, a fundamental hybridization process and exchange energies contribute to the emergence of ferromagnetism due to electron-spin interactions. Finally, assessments of electrical and thermal conductivities, Seebeck coefficient, power factor, figure of merit and magnetic susceptibility are conducted to assess the potential of the investigated materials for the applications in thermoelectric devices.

Double Perovskite Single Crystals with High Laser Irradiation Stability for Solid-State Laser Lighting and Anti-counterfeiting

Laser lighting devices, comprising an ultraviolet (UV) laser chip and a phosphor material, have emerged as a highly efficient approach for generating high-brightness light sources. However, the high power density of laser excitation may exacerbate thermal quenching in conventional polycrystalline or amorphous phosphors, leading to luminous saturation and the eventual failure of the device. Here, for the first time, we raise a single-crystal (SCs) material for laser lighting considering the absence of grain boundaries that scatter electrons and phonons, achieving high thermal conductivity (0.81 W m-1 K-1) and heat-resistance (575 °C). The SCs products exhibit a high photoluminescence quantum yield (89%) as well as excellent stability toward high-power lasers (>12.41 kW/cm2), superior to all previously reported amorphous or polycrystalline matrices. Finally, the laser lighting device was fabricated by assembling the SC with a UV laser chip (50 mW), and the device can maintain its performance even after continuous operation for 4 h. Double perovskite single crystals doped with Yb3+/Er3+ demonstrated multimodal luminescence with the irradiation of 355 and 980 nm lasers, respectively. This characteristic holds significant promise for applications in spectrally tunable laser lighting and multimodal anticounterfeiting.

An all-inorganic lead-free metal halide double perovskite for the highly selective detection of norfloxacin in aqueous solution

Lead-based perovskites are highly susceptible to environmental influences, and their application in analytical chemistry, especially in aqueous solution, has been reported rarely. All-inorganic lead-free metal halide perovskites have been considered as a substitute for lead-based perovskites. Herein, a Cs2RbTbCl6 perovskite microcrystal (PMCs), which emits strong yellow-green fluorescence with a maximum emission wavelength at 547 nm, was for the first time  synthesized and characterized. The Cs2RbTbCl6 PMCs could be well dispersed in N,N-dimethylacetamide (DMF), and its fluorescence could be significantly enhanced by the addition of norfloxacin (NOR) in the aqueous solution. We found that the Cs2RbTbCl6 PMCs can be used as fluorescent probes (excitation, 365 nm; emission, 547 nm) to selectively detect NOR in a concentration range from 10.0 to 200.0 μM with the limit of detection (LOD) being 0.04 μM. The Cs2RbTbCl6 PMCs could also be adsorbed on filter paper to fabricate as a fluorescent test paper for visual detection of NOR under 365-nm ultraviolet (UV) lamp irradiation. The proposed method has the potential to establish a new analytical method to visualize the detection of NOR in aqueous environments and also promotes the application of all-inorganic lead-free perovskites for analytical detection in aqueous environments.

Regulating Exciton De-Trapping of Te4+ -Doped Zero-Dimensional Scandium-Halide Perovskite for Fluorescence Thermometry with Record High Time-Resolved Thermal Sensitivity

Fluorescence thermometry has been propelled to the forefront of scientific attention due to its high spatial resolution and remote non-invasive detection. However, recent generations of thermometers still suffer from limited thermal sensitivity (Sr ) below 10% change per Kelvin. Herein, this work presents an ideal temperature-responsive fluorescence material through Te4+ -doped 0D Cs2 ScCl5 ·H2 O, in which isolated polyhedrons endow highly localized electronic structures, and the strong electron-phonon coupling facilitates the formation of self-trapped excitons (STEs). With rising temperature, the dramatic asymmetric expansion of the soft lattice induces increased defects, strong exciton-phonon coupling, and low thermal activation energy, which evokes a rapid de-trapping process of STEs, enabling several orders of magnitude changes in the fluorescence lifetime over a narrow temperature range. After regulating the de-trapping process with different Te4+ doping, a record-high Sr (27.36% K-1 ) of fluorescence lifetime-based detection is achieved at 325 K. The robust stability against multiple heating/cooling cycles and long-term measurements enables a low temperature uncertainty of 0.067 K. Further, the developed thermometers are demonstrated for the remote local monitoring of operating temperature on internal electronic components. It is believed that this work constitutes a solid step towards building the next generation of ultrasensitive thermometers based on low-dimensional metal halides.

Targeted high-precision up-converting thermometer platform over multiple temperature zones with Er3

Ratiometric luminescence thermometry based on trivalent erbium ions is a noninvasive remote sensing technique with high spatial and temporal resolution. The thermal coupling between two adjacent energy levels follows the Boltzmann statistics, whose effective range is related to the energy gap between the multi-excited states. However, the limitations of different thermally coupled levels (TCLs) in Er-based thermometers are rarely mentioned. Here, a type of targeted high-precision luminescence thermometer was designed using a lead-free double perovskite platform by selecting multiple TCLs of the Er³⁺ ion. According to the selection of different TCLs in a single system platform, more precise temperature resolution can be obtained in different temperature regions from 100 K to almost 880 K. This work provides a quantitative guideline that may pave the way for the development of the next generation of temperature sensor based on trivalent erbium ions.

Multimodal Luminescent Low-Dimension Cs2ZrCl6:xSb3+ Crystals for White Light-Emitting Diodes and Information Encryption

Low-dimension perovskite materials have attracted wide attention due to their excellent optical properties and stability. Herein, Sb³⁺-doped Cs₂ZrCl₆ crystals are synthesized by a coprecipitation method in which Sb³⁺ ions partially replace Zr⁴⁺ ions. The Cs₂ZrCl₆:xSb³⁺ powder shows blue and orange-red emissions under a 254 and 365 nm light, respectively, due to the [ZrCl₆]^2- octahedron and [SbCl₆]^3- octahedron. The photoluminescence quantum yield (PLQY) of Cs₂ZrCl₆:xSb³⁺ (x = 0.1) crystals is up to 52.5%. According to experimental and computational results, the emission mechanism of the Cs₂ZrCl₆:xSb³⁺ crystals is proposed. On the one hand, a wide blue emission with a large Stokes shift is caused by the self-trapping excitons of [ZrCl₆]^2- octahedra under a 260 nm excitation. On the other hand, the luminescence mechanism of [SbCl₆]^3- octahedron is divided into two parts: ¹P₁ → ¹S₀ (490 nm) and ³P₁ → ¹S₀ (625 nm). The broad-band emission, high PLQY, and excellent stability endow the Cs₂ZrCl₆:xSb³⁺ powders with the potential for the fabrication of white light-emitting diodes (WLEDs). A WLED device is fabricated using a commercial 310 nm NUV chip, which shows a high color rendering index of 89.7 and a correlated color temperature of 5333 K. In addition, the synthesized Cs₂ZrCl₆:xSb³⁺ crystals can be also successfully used for information encryption. Our work will provide a deep understanding of the photophysical properties of Sb³⁺-doped perovskites and facilitate the development of Cs₂ZrCl₆:xSb³⁺ crystals in encrypting multilevel optical codes and WLEDs.

Ultrasensitive Optical Thermometry via Inhibiting the Energy Transfer in Zero-Dimensional Lead-Free Metal Halide Single Crystals

Self-referencing optical thermometry based on the fluorescence intensity ratio (FIR) have drawn extensive attention as a result of their high sensitivity and non-invasively fast response to temperature. However, it is a great challenge for luminescent materials to achieve simultaneously high absolute and relative temperature sensitivity based on the FIR technique. Herein, we developed a novel optical thermometer by designing hybrid lead-free metal halide (TTPhP)₂MnCl₄:Sb³⁺ (TTPhP⁺ = tetraphenylphosphonium cation) single crystals with multimodal photoluminescence (PL). The large TTPhP⁺ organic chain resulted in isolated [MnCl₄]^2- and [SbCl₅]^2- in the single crystal, which leads to a negligible energy trasfer process within them. Therefore, the two PL bands (band 1 from [MnCl₄]^2-) with a peak at 518 nm and band 2 (from [SbCl₅]²) with a peak at 640 nm exhibit different thermal-quenching effects, which resulted in excellent temperature sensitivity, with the maximum absolute and relative sensitivities reaching 0.236 K^-1 and 3.77% K^-1 in a temperature range from 300 to 400 K. Both the absolute and relative sensitivities are among the highest values for luminescence thermometry.

Fast HCl-free Synthesis of Lead-free Rb2ZrCl6:xSb3+ Perovskites

Due to the toxicity and instability issues of lead halide perovskites, lead-free perovskites have recently emerged as a viable alternative. However, significant optical band gaps of lead-free perovskites exert influence on their luminescent properties. Fortunately, the addition of dopants becomes an efficacious solution. The current widely utilized methods for synthesizing perovskites almost require high temperatures, a long period, and atmosphere protection, which cost more energy and resources. In this paper, we report that Rb₂ZrCl₆:xSb³⁺ perovskite phosphors can be easily prepared by a wet grinding approach at room temperature, which is a more efficient and facile process. Due to the self-trapped excitons of the host structure and Sb³⁺ ions, the produced samples display blue-white and orange fluorescence under UV lamp irradiation at 254 and 365 nm, respectively. In the photoluminescence spectrum, the doped perovskite exhibits an emission peak at 630 nm under excitation at 365 nm. Importantly, the prepared phosphors have tunable emissions related to the excitation wavelength. In addition, our produced powders show remarkable stability at room temperature, laying the foundations for this approach to be widely used in perovskite production.