Temperature-Dependent Photoluminescence of Hexafluorobenzene-Intercalated Phenethylammonium Tin Iodide 2D Perovskite

Tin halide perovskites are potential alternatives of lead halide perovskites. However, the easy oxidation of Sn²⁺ to Sn⁴⁺ brings in a challenge. Recently, layered two-dimensional hybrid tin halide perovskites have been shown to partially resist the oxidation process because of the presence of hydrophobic organic molecules. Consequently, such layered hybrid perovskites are being explored for optoelectronic applications. The optical properties of layered tin halide perovskites depend on the interlayer separation and the dielectric mismatch between the organic and inorganic layers. Intercalation (insertion) of a molecular species between the layers modifies the interlayer interactions affecting the optical properties of layered hybrid perovskites. We investigated the effect of hexafluorobenzene (HFB) intercalation in phenethylammonium tin iodide [(PEA)₂SnI₄] using temperature-dependent (6 K to 300 K) photoluminescence (PL). HFB intercalation increases the bandgap. A strong PL quenching is observed in pristine (PEA)₂SnI₄ below 150 K, probably because of the presence of non-emissive states. HFB intercalation suppresses the influence of such non-emissive states resulting in an increase in PL intensity at the cryogenic temperatures. Our results highlight that a simple molecular intercalation (non-covalent interaction) into layered hybrid perovskites can significantly tailor the electronic and optical properties.     

Photoluminescence in disordered Zn2TiO4

In this work, the polymeric precursor method was used to obtain disordered Zn₂TiO₄ powders, either undoped or doped with Sn⁴⁺, Cr³⁺ and V⁵⁺, to be applied as photoluminescent material. The characterization was undertaken by means of thermal analysis (TG and DTA), X-ray diffraction (XRD), infrared spectroscopy (IR) and photoluminescence (PL). Previous works stated that titanate octahedra containing a short Ti-O distance show efficient luminescence at room temperature if these octahedra are isolated from each other. In the present work, the phenomenon was observed in condensed octahedra, sharing edges. The room temperature PL noticed in undoped Zn₂TiO₄ had its intensity increased by the dopant addition—the increase was of about 300% for V⁵⁺ doping, 400% for Cr³⁺ and 800% for Sn⁴⁺.     

Lead‐Free,Blue Emitting Bismuth Halide Perovskite Quantum Dots

Lead halide perovskite quantum dots (QDs) are promising candidates for future lighting applications, due to their high quantum yield, narrow full width at half maximum (FWHM), and wide color gamut. However, the toxicity of lead represents a potential obstacle to their utilization. Although tin(II) has been used to replace lead in films and QDs, the high intrinsic defect density and oxidation vulnerability typically leads to unsatisfactory material properties. Bismuth, with much lower toxicity than lead, is promising to constitute lead‐free perovskite materials because Bi³⁺ is isoelectronic to Pb²⁺ and more stable than Sn²⁺. Herein we report, for the first time, the synthesis and optical characterization of MA₃Bi₂Br₉ perovskite QDs with photoluminescence quantum yield (PLQY) up to 12 %, which is much higher than Sn‐based perovskite nanocrystals. Furthermore, the photoluminescence (PL) peaks of MA₃Bi₂X₉ QDs could be easily tuned from 360 to 540 nm through anion exchange.     

Lead‐Free,Blue Emitting Bismuth Halide Perovskite Quantum Dots

Lead halide perovskite quantum dots (QDs) are promising candidates for future lighting applications, due to their high quantum yield, narrow full width at half maximum (FWHM), and wide color gamut. However, the toxicity of lead represents a potential obstacle to their utilization. Although tin(II) has been used to replace lead in films and QDs, the high intrinsic defect density and oxidation vulnerability typically leads to unsatisfactory material properties. Bismuth, with much lower toxicity than lead, is promising to constitute lead‐free perovskite materials because Bi³⁺ is isoelectronic to Pb²⁺ and more stable than Sn²⁺. Herein we report, for the first time, the synthesis and optical characterization of MA₃Bi₂Br₉ perovskite QDs with photoluminescence quantum yield (PLQY) up to 12 %, which is much higher than Sn‐based perovskite nanocrystals. Furthermore, the photoluminescence (PL) peaks of MA₃Bi₂X₉ QDs could be easily tuned from 360 to 540 nm through anion exchange.     

Preparation, crystal structure, and photoluminescence of Ca2SnO4:Eu, Y

Eu³⁺-doped Ca₂SnO₄ (solid solutions of Ca_2−xEu_2xSn_1−xO₄, 0?x?0.3) and Eu³⁺ and Y³⁺-codoped Ca₂SnO₄ (Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄) were prepared by solid-state reaction at 1400 °C in air. Rietveld analysis of the X-ray powder diffraction patterns revealed that Eu³⁺ replaced Ca²⁺ and Sn⁴⁺ in Eu³⁺-doped Ca₂SnO₄, and that Eu³⁺ replaced Ca²⁺ and Y³⁺ replaced Sn⁴⁺ in Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄. Red luminescence at 616 nm due to the electric dipole transition ⁵D_o→⁷F₂ was observed in the photoluminescence (PL) spectra of Ca_2−xEu_2xSn_1−xO₄ and Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄ at room temperature. The maximum PL intensity in the solid solutions of Ca_2−xEu_2xSn_1−xO₄ was obtained for x=0.1. The PL intensity of Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄ was 1.26 times greater than that of Ca_2−xEu_2xSn_1−xO₄ with x=0.1.     

Highly stable metal halides Cs2ZnX4 (X = Cl,Br) with Sn2+ as dopants for efficient deep-red photoluminescence

The development of deep-red emitting lead-free metal-halide perovskites with high photoluminescence quantum yields (PLQYs) and outstanding stability remains a major challenge for displays and deep-tissue bioimaging. In this work, we report a facile and convenient solvothermal method to synthesize metal halides Cs₂ZnX₄ (X = Cl, Br) that however is PL innert at room temperature. Upon composition engineering utilizing Sn²⁺ as the dopant, the resulting Cs₂ZnCl₄:Sn not only emits strong deep-red PL peaked at 700 nm with the highest 99.4% PLQY among the similar materials so far, but also exhibits excellent structure stability in air (PLQY remains 96% after one year exposure to the atmosphere). Detailed experimental characterizations and theoretical calculations reveal that the deep-red emission stems from self-trapped excitons induced by the Sn²⁺ dopant. Particularly, triplet emission (³P₂→¹S₀) from Sn-5s² orbitals has been observed at low temperature due to the break of parity-forbidden transition. This work provides an important guidance for the development of deep-red light-emitting materials with low price, high efficiency and excellent stability.     

Near‐Infrared Emission from Tin–Lead (Sn–Pb) Alloyed Perovskite Quantum Dots by Sodium Doping

Phase‐stable CsSn_xPb_1?xI₃ perovskite quantum dots (QDs) hold great promise for optoelectronic applications owing to their strong response in the near‐infrared region. Unfortunately, optimal utilization of their potential is limited by the severe photoluminescence (PL) quenching, leading to extremely low quantum yields (QYs) of approximately 0.3 %. The ultra‐low sodium (Na) doping presented herein is found to be effective in improving PL QYs of these alloyed QDs without alerting their favourable electronic structure. X‐ray photoelectron spectroscopy (XPS) studies suggest the formation of a stronger chemical interaction between I^? and Sn²⁺ ions upon Na doping, which potentially helps to stabilize Sn²⁺ and suppresses the formation of I vacancy defects. The optimized PL QY of the Na‐doped QDs reaches up to around 28 %, almost two orders of magnitude enhancement compared with the pristine one.     

Near-Infrared Emission from Tin–Lead (Sn–Pb) Alloyed Perovskite Quantum Dots by Sodium Doping

Phase-stable CsSn_xPb_1−xI₃ perovskite quantum dots (QDs) hold great promise for optoelectronic applications owing to their strong response in the near-infrared region. Unfortunately, optimal utilization of their potential is limited by the severe photoluminescence (PL) quenching, leading to extremely low quantum yields (QYs) of approximately 0.3 %. The ultra-low sodium (Na) doping presented herein is found to be effective in improving PL QYs of these alloyed QDs without alerting their favourable electronic structure. X-ray photoelectron spectroscopy (XPS) studies suggest the formation of a stronger chemical interaction between I⁻ and Sn²⁺ ions upon Na doping, which potentially helps to stabilize Sn²⁺ and suppresses the formation of I vacancy defects. The optimized PL QY of the Na-doped QDs reaches up to around 28 %, almost two orders of magnitude enhancement compared with the pristine one.     

High‐Performance CsPb1−xSnxBr3 Perovskite Quantum Dots for Light‐Emitting Diodes

All inorganic CsPbBr₃ perovskite quantum dots (QDs) are potential emitters for electroluminescent displays. We have developed a facile hot‐injection method to partially replace the toxic Pb²⁺ with highly stable Sn⁴⁺. Meanwhile, the absolute photoluminescence quantum yield of CsPb_1−x Sn_x Br₃ increased from 45 % to 83 % with Sn^IV substitution. The transient absorption (TA) exciton dynamics in undoped CsPbBr₃ and CsPb_0.67Sn_0.33Br₃ QDs at various excitation fluences were determined by femtosecond transient absorption, time‐resolved photoluminescence, and single‐dot spectroscopy, providing clear evidence for the suppression of trion generation by Sn doping. These highly luminescent CsPb_0.67Sn_0.33Br₃ QDs emit at 517 nm. A device based on these QDs exhibited a luminance of 12 500 cd m⁻², a current efficiency of 11.63 cd A⁻¹, an external quantum efficiency of 4.13 %, a power efficiency of 6.76 lm w⁻¹, and a low turn‐on voltage of 3.6 V, which are the best values among reported tin‐based perovskite quantum‐dot LEDs.     

Fabrication and optical properties of core-shell structured spherical SiO2@GdVO4:Eu phosphors via sol-gel process

Europium-doped nanocrystalline GdVO₄ phosphor layers were coated on the surface of preformed submicron silica spheres by sol-gel method. The resulted SiO₂@Gd_0.95Eu_0.05VO₄ core-shell particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, low voltage cathodoluminescence (CL), time resolved PL spectra and kinetic decays. The XRD results demonstrate that the Gd_0.95Eu_0.05VO₄ layers begin to crystallize on the SiO₂ spheres after annealing at 600 ^°C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have spherical shape, narrow size distribution (average size ca. 600 nm), non-agglomeration. The thickness of the Gd_0.95Eu_0.05VO₄ shells on the SiO₂ cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). PL and CL show that the emissions are dominated by ⁵D₀-⁷F₂ transition of Eu³⁺ (618 nm, red). The PL and CL intensities of Eu³⁺ increase with increasing the annealing temperature and the number of coating cycles. The optimum concentration for Eu³⁺ was determined to be 5 mol% of Gd³⁺ in GdVO₄ host.     

不同浓度Sn4+离子掺杂TiO2的结构、性质和光催化活性

采用溶胶-凝胶法制备出纯TiO₂和不同浓度Sn⁴⁺离子掺杂的TiO₂光催化剂(TiO₂-Snx%, x%代表Sn⁴⁺离子掺杂的TiO₂样品中Sn⁴⁺离子摩尔分数). 利用X 射线衍射(XRD)、X 射线光电子能谱(XPS)和表面光电压谱(SPS)确定了TiO₂-Snx%催化剂的晶相结构和能带结构, 结果表明: 当Sn⁴⁺离子浓度较低时, Sn⁴⁺离子进入TiO₂晶格, 取代并占据Ti⁴⁺离子的位置, 形成取代式掺杂结构(Ti_1-xSn_xO₂), 其掺杂能级在导带下0.38 eV处; 当Sn⁴⁺离子浓度较高时, 掺入的Sn⁴⁺离子在TiO₂表面生成金红石SnO₂, 形成TiO₂和SnO₂复合结构(TiO₂/SnO₂), SnO₂的导带位于TiO₂导带下0.33 eV处. 利用瞬态光电压谱和荧光光谱研究了TiO₂-Snx%催化剂光生载流子的分离和复合的动力学过程, 结果表明, Sn⁴⁺离子掺杂能级和表面SnO₂能带存在促进光生载流子的分离, 有效地抑制了光生电子与空穴的复合; 然而, Sn⁴⁺离子掺杂能级能更有效地增加光生电子的分离寿命, 提高了光生载流子的分离效率, 从而揭示了TiO₂-Snx%催化剂的光催化机理.     

Exciton Localization for Highly Luminescent Two-Dimensional Tin-Based Hybrid Perovskites through Tin Vacancy Tuning

Exciton localization is an approach for preparing highly luminescent semiconductors. However, realizing strongly localized excitonic recombination in low-dimensional materials such as two-dimensional (2D) perovskites remains challenging. Herein, we first propose a simple and efficient Sn²⁺ vacancy (V_Sn) tuning strategy to enhance excitonic localization in 2D (OA)₂SnI₄ (OA=octylammonium) perovskite nanosheets (PNSs), increasing their photoluminescence quantum yield (PLQY) to ≈64 %, which is among the highest values reported for tin iodide perovskites. Combining experimental with first-principles calculation results, we confirm that the significantly increased PLQY of (OA)₂SnI₄ PNSs is primarily due to self-trapped excitons with highly localized energy states induced by V_Sn. Moreover, this universal strategy can be applied for improving other 2D Sn-based perovskites, thereby paving a new way to fabricate diverse 2D lead-free perovskites with desirable PL properties.     

Quantitative determination of site occupancy of multi-rare-earth elements doped into Ca2SnO4 phosphor by electron channeling microanalysis

X-ray fluorescence analysis based on electron channeling effects in transmission electron microscopy (TEM) was performed on Ca₂SnO₄ phosphor materials doped with Eu³⁺/Y³⁺ at various concentrations, which showed red photoluminescence associated with the ⁵D₀-⁷F₂ electric dipole transition of Eu³⁺ ions. The method provided direct information on which host element site dopant elements occupy, the results of which were compared with those of X-ray diffraction (XRD)-Rietveld analysis. The obtained results indicated that while it is not favorable for a part of Eu³⁺ to occupy the smaller Sn⁴⁺ site, this is still energetically better than creating Ca vacancies or any other of the possible charge balance mechanisms. The local lattice distortions associated with dopant impurities with different ionic radii were also examined by TEM-electron energy-loss spectroscopy (TEM-EELS). The change in PL intensity as a function of dopant concentration is discussed based on the experimental results, although the general concept of concentration quenching applies.     

The Rb7Bi3−3xSb3xCl16 Family: A Fully Inorganic Solid Solution with Room-Temperature Luminescent Members

Low-dimensional ns²-metal halide compounds have received immense attention for applications in solid-state lighting, optical thermometry and thermography, and scintillation. However, these are based primarily on the combination of organic cations with toxic Pb²⁺ or unstable Sn²⁺, and a stable inorganic luminescent material has yet to be found. Here, the zero-dimensional Rb₇Sb₃Cl₁₆ phase, comprised of isolated [SbCl₆]³⁻ octahedra and edge-sharing [Sb₂Cl₁₀]⁴⁻ dimers, shows room-temperature photoluminescence (RT PL) centered at 560 nm with a quantum yield of 3.8±0.2 % at 296 K (99.4 % at 77 K). The temperature-dependent PL lifetime rivals that of previous low-dimensional materials with a specific temperature sensitivity above 0.06 K⁻¹ at RT, making it an excellent thermometric material. Utilizing both DFT and chemical substitution with Bi³⁺ in the Rb₇Bi_3−3xSb_3xCl₁₆ (x≤1) family, we present the edge-shared [Sb₂Cl₁₀]⁴⁻ dimer as a design principle for Sb-based luminescent materials.     

Additive assisted hydrothermal synthesis,characterization and optical properties of one dimensional DyPO4:Ce3+ nanostructures

One dimensional nanostructures of cerium doped dysprosium phosphate (DyPO₄:Ce³⁺) were synthesized via hydrothermal route in the presence of different surfactants [sodium dodecyl sulfate (SDS), dodecyl sulfosuccinate (DSS), polyvinyl pyrollidone (PVP)] and solvent [ethylene glycol and water]. The prepared nanostructures were characterized by Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), UV-VIS-NIR absorption spectrophotometer and photoluminescence (PL) studies. The PXRD and FTIR results indicate purity, good crystallinity and effective doping of Ce³⁺ in nanostructures. SEM and TEM micrographs display nanorods, nanowires and nanobundles like morphology of DyPO₄:Ce³⁺. Energy-dispersive X-ray spectra (EDS) of DyPO₄:Ce³⁺nanostructures confirm the presence of dopant. UV-VIS-NIR absorption spectra of prepared compounds are used to calculate band gap and explore their optical properties. Luminescent properties of DyPO₄:Ce³⁺ was studied by using PL emission spectra. The effect of additives and solvents on the uniformity, morphology and optical properties of the nanostructures were studied in detail.     

Optical Spectroscopy and Excited-State Dynamics of Eu3+-Doped Bismuth Borate Glasses Containing CuO

Bismuth borate glasses containing phosphors and luminescent rare-earths are of interest for applications in light-emitting devices. Herein, the influence of CuO impurities on red-emitting Eu³⁺-doped bismuth borate glasses of the 25Bi₂O₃-15BaO-10Li₂O-50B₂O₃ type was investigated by various spectroscopic methods. The glasses were prepared by the melt-quench technique and characterized by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, UV/Vis optical absorption (OA), and photoluminescence (PL) spectroscopy including decay kinetics assessment. The XRD data confirmed the amorphous nature of the glasses whereas FT-IR spectra indicated the basic structural features of trigonal BO₃ units and BO₄ tetrahedra. The OA analysis showed that addition of CuO up to 0.5 mol% results in significant growth of the visible Cu²⁺ absorption band around 715 nm, with slight decrease in the optical band gap energies assessed through Tauc plots. A drastic PL quenching of Eu³⁺ ions emission was evidenced concurring with the detrimental effect of Cu²⁺. The assessment of the Eu³⁺ emission decay curves revealed significant lifetime decrease of the ⁵D₀ emitting state with increasing CuO concentration. An analysis of quenching constants was finally performed comparing results from integrated PL data with the emission decay rates. It is argued that the bismuth borate glass system supports an effective Eu³⁺→Cu²⁺ energy transfer (more so than phosphates) in connection with a strong spectral overlap between Eu³⁺ emission and Cu²⁺ absorption.     

The Rb7Bi3−3xSb3xCl16 Family: A Fully Inorganic Solid Solution with Room‐Temperature Luminescent Members

Low‐dimensional ns²‐metal halide compounds have received immense attention for applications in solid‐state lighting, optical thermometry and thermography, and scintillation. However, these are based primarily on the combination of organic cations with toxic Pb²⁺ or unstable Sn²⁺, and a stable inorganic luminescent material has yet to be found. Here, the zero‐dimensional Rb₇Sb₃Cl₁₆ phase, comprised of isolated [SbCl₆]^3? octahedra and edge‐sharing [Sb₂Cl₁₀]^4? dimers, shows room‐temperature photoluminescence (RT PL) centered at 560 nm with a quantum yield of 3.8±0.2 % at 296 K (99.4 % at 77 K). The temperature‐dependent PL lifetime rivals that of previous low‐dimensional materials with a specific temperature sensitivity above 0.06 K^?1 at RT, making it an excellent thermometric material. Utilizing both DFT and chemical substitution with Bi³⁺ in the Rb₇Bi_3?3xSb_3xCl₁₆ (x≤1) family, we present the edge‐shared [Sb₂Cl₁₀]^4? dimer as a design principle for Sb‐based luminescent materials.     

Influence of annealing temperature on material properties of red emitting ZnGa<Subscript>2</Subscript>O<Subscript>4</Subscript>: Cr<Superscript>3+</Superscript> nanostructures

Zinc gallate (ZnGa₂O₄) nanopowders doped with Cr³⁺ (1?mo%) were synthesized by the citric acid assisted sol–gel method. The influence of annealing temperature, structural, morphological, and optical properties of ZnGa₂O₄: Cr³⁺ (1?mol%) nanosized particles were investigated. The X-ray diffraction (XRD) spectra indicated that the nanoparticles are cubic in structure and the annealing temperature did not influence any c in structure. The average crystallite size of ZnGa₂O₄: Cr³⁺ nanoparticles were observed to increase from 11.85 to 30.88?nm as the annealing temperature increased from 600 to 1000?°C. The scanning electron microscopy (SEM) showed nearly spherical nanostructures that change in size with annealing temperature. The high resolution transmission electron microscope (HR-TEM) images show well resolved lattice fringes which is an indications of highly crystalline samples. Ultraviolet–visible (UV–Vis) measurement show decrease in reflectance in visible region and energy band gap was found to decrease with annealing temperature. The photoluminescence (PL) intensity was found to be maximum for sample annealed at high temperature (1000?°C) and least with sample annealed at low temperature (600?°C). An increase in annealing temperature leads significantly increment in PL intensity. The degree of crystallinity also increased with annealing temperature from XRD, SEM, and HR-TEM analysis. The photoluminescence lifetimes, particle size, and emission spectra are comparable with reports on bioimaging applications.

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Distribution-related luminescence of Eu sensitized by SnO2 nano-crystals embedding in oxide glassy matrix

Eu³⁺ doped transparent glass ceramics embedding SnO₂ nano-crystals were prepared by melt quenching and subsequent heating. Site selective excitation experiments revealed that some Eu³⁺ ions were incorporated in the SnO₂ lattices by substituting Sn⁴⁺ ions, whereas the rest located in the oxide glassy matrix. Interestingly, it is found that the Eu³⁺ ions residing in the SnO₂ lattices exhibited much longer luminescent decay lifetime than those in the glassy matrix. Measurements on the photoluminescence excitation and photoluminescence spectra demonstrated the occurrence of energy transfer from the SnO₂ nano-crystals to the Eu³⁺ ions. The influences of Eu³⁺ content, and furthermore, their location on the energy transfer process were discussed.     

Structure and optical properties of cerium(III)-doped PbWO4 micro-crystals synthesized by a facile wet chemical method

Cerium(III) doped PbWO₄ micro-crystals with different doping contents were synthesized via a facile wet chemical method in air atmosphere at room temperature. X-ray diffraction patterns of as-synthesized powders revealed that these micro-crystals were pure scheelite PbWO₄, without any impurities such as Ce₂(WO₄)₃ and PbO, and Ce³⁺ could enter into Pb²⁺ sites, which would induce the formation of lead vacancies in the PbWO₄ crystal lattice. The UV–vis diffuse reflection spectra, Raman spectra and photoluminescence (PL) spectra of doped and pure PbWO₄ micro-crystals were studied in detail, which indicated that optical properties of doped PbWO₄ were greatly changed. The adsorption edge of Ce(III)-doped PbWO₄ micro-crystals would shift toward high wavelength (red-shift) with gradually increasing Ce³⁺ doping concentration. It shows an obvious decrease in blue emission band which made the shape of the whole emission band remodeled with the Ce³⁺ doping.