Cubic Halide Double Perovskite Nanocrystals with Anisotropic Free Excitons and Self-Trapped Exciton Photoluminescence

Excitation-Dependent Emission in Sb3+-Doped All-Inorganic Rare-Earth Double Perovskites for Anticounterfeiting Applications

Achieving high-efficiency tunable emission in a single phosphor remains a significant challenge. Herein, we report a series of Sb3+-doped all-inorganic double perovskites, Sb3+:Cs2NaScCl6, with efficient excitation-dependent emission. In 0.5%Sb3+:Cs2NaScCl6, strong blue emission with a high photoluminescence quantum yield (PLQY) of 85% is obtained under 265 nm light irradiation, which turns into bright neutral white light with a PLQY of 56% when excited at 303 nm. Spectroscopic and computational investigations were performed to reveal the mechanism of this excitation-dependent emission. Sb3+ doping induces two different excitation channels: the internal transition of Sb3+: 5s2 → 5s5p and the electron transfer transition of Sb3+: 5s → Sc3+ 3d. The former one generates excited Sb3+ ions, which can undergo efficient energy transfer to populate the host self-trapped exciton (STE) state, yielding enhanced blue emission. The latter one leads to the formation of a new STE state with the hole localized on Sb3+ and the electron delocalized on the nearest Sc3+, which accounts for the newly exhibited low-energy emission. The difference in the excitation pathways of the two emitting STE states results in the highly efficient excitation-dependent emission, making the doped systems promising anticounterfeiting materials.

Electronically Temperature-Dependent Interplay between He and Trivacancy in Tungsten Plasma-Facing Materials

Both microvoids and helium (He) impurities are widely present in tungsten (W) plasma-facing materials (PFMs), where the interaction between microvoids and He atoms has led to the intriguing development of microvoids. In this paper, we comprehensively investigated the interaction between He atoms and trivacancy (V3), a fundamental microvoid in W-PFMs, at the level of tight-binding theory. Our study showed that He atoms can catalyze the decomposition of the original V3 or facilitate its transformation into another V3 variant. We propose that a He atom near the V3 defect induces significant changes in the distribution of d-electron charges within the W atoms lining the inner wall of the V3 defect, making the W atom nearest to this He atom cationic and the other W atoms anionic. The attractive interaction between them promotes the decomposition and deformation of V3. As electronic excitation increases, the ionization of W atoms on the V3 wall gradually intensifies, thereby enhancing the cationic characteristics of the W atoms closest to the He atom. This process also prompts other W atoms to shift from anions to cations, leading to a transition in the electrostatic interactions between them from attraction to repulsion. This transformation, driven by electronic excitation, plays a significant inhibitory role in the decomposition and deformation of V3.

Lattice Distortion and Low-Frequency Anharmonic Phonons Suppress Charge Recombination in Lead Halide Perovskites upon Pseudohalide Doping: Time-Domain Ab Initio Analysis

Perovskite solar cells have witnessed a surge in interest as a promising technology for low-cost, high-efficiency photovoltaics with certified power conversion efficiencies beyond 25%. However, their commercial development is hindered by poor stability and nonradiative losses that restrict their approach to the theoretical efficiency limit. Using ab initio nonadiabatic molecular dynamics, we demonstrate that nonradiative charge recombination is suppressed when the iodide in formamidinium lead iodide (FAPbI3) is partially replaced with pseudohalide anions (SCN-, BF4-, and PF6-). The replacement breaks the symmetry of the system and creates local structural distortion and dynamic disorder, decreasing electron-hole overlap and nonadiabatic electron-vibrational coupling. The charge carrier lifetime is found to increase with increased structural distortion and is the longest for PF6-. This work is fundamentally relevant to the design of high-performance perovskite materials for optoelectronic applications.

Lead-Free Zero-Dimensional Zn-Based Metal Halides of Highly Efficient Blue Luminescence from Self-Trapping Exciton

Recently, hybrid metal halides have received great attention in the field of solid-state lighting because of their diverse structures and excellent photoluminescence properties. In this work, we first reported two hybrid zinc-based metal halides with zero-dimensional structures, (BMPP)₂ZnBr₄ and (TBA)₂ZnBr₄, which exhibited broadband emission with large Stokes shifts. Notably, the highest photoluminescence quantum yield of 59.76% was observed. Additionally, the luminescence mechanism of metal halides was investigated by using time-resolved femtosecond transient absorption experiments. A broad excited-state absorption platform with the tendency of slowly decaying was shown in the detection range, demonstrating that after the electrons were excited to the excited state, the free excitons underwent a nonadiabatic transition to self-trapped excitons and went through a radiation recombination process to the ground state. A blue-light-emitting diode could be easily obtained by coating (BMPP)₂ZnBr₄ on a GaN chip, which indicated that it has good competitiveness in the application of solid-state lighting devices.

Modulating the afterglow time of Mn2+ doped double perovskites by size tuning and its applications in dynamic information display

Mn²⁺ doped lead-free double perovskites are emerging afterglow materials that can avoid the usage of rare earth ions. However, the regulation of the afterglow time is still a challenge. In this work, the Mn doped Cs₂Na_0.2Ag_0.8InCl₆ crystals with afterglow emission at about 600 nm are synthesized by a solvothermal method. Then, the Mn²⁺ doped double perovskite crystals are crushed into different sizes. As the size decreases from 1.7 mm to 0.075 mm, the afterglow time decreases from 2070 s to 196 s. Steady-state photoluminescence (PL) spectra, time resolved PL, thermoluminescence (TL) reveal the afterglow time monotonously decreases due to the enhanced nonradiative surface trapping. The modulation on afterglow time will greatly promote their applications in various fields, such as bioimaging, sensing, encryption, and anti-counterfeiting. As a proof of concept, dynamic display of information is realized based on different afterglow times.

Phase transition-induced initial decomposition of nitrogen-rich binary CN compound 2,2'-azobis(5-azidotetrazole) and its precursor 2-amino-5-azidotetrazole via tetrazole ring opening under external electric fields: a comparative DFT-D study

A comparative DFT-D study was performed to investigate the external electric field-induced crystal structures, electronic features, Hirshfeld surfaces, vibrational properties and initial decomposition mechanisms of nitrogen-rich binary CN compound 2,2'-azobis(5-azidotetrazole) (C₂N₁₆) and its precursor 2-amino-5-azidotetrazole (CH₂N₈). The results show that there exist phase transitions at the critical points of 0.006 a.u. and 0.008 a.u. for CH₂N₈ and C₂N₁₆, respectively, which are embodied in various properties of these compounds and induce their initial decomposition of the tetrazole ring opening via the breaking of N-N single bonds. The analysis of band gaps and density of states suggests the external electric field-induced enhancing ability for electron transition from the occupied orbitals to empty ones and N-N bond breaking may be the initial decomposition pathway for them. The variations in Hirshfeld surfaces indicate the spatial change and adjustment of non-bonding interactions in the two crystals. The discussions on vibrational properties indicate that IR characteristic peaks of all vibrational modes in the two crystals show a gradual red shift toward a low frequency region. The external electric field-induced initial decomposition pathways of both crystals are tetrazole ring opening via the breaking of a N-N single bond. Our findings provide insights for a comprehensive understanding of external electric field-induced phase transition and initial decomposition mechanisms of nitrogen-rich binary CN energetic compounds.

Ion Substitution Strategy toward High-Efficiency Near-Infrared Photoluminescence of Cs2KIn1-yAlyF6:Cr3+ Solid Solutions

The rising demand for portable near-infrared (NIR) light sources has accelerated the exploration of NIR luminescent materials with high efficiency and excellent thermal stability. Inspired by the structural-modulated ion substitution strategy, herein, a high-performance Cs₂KIn_0.8Al_0.1F₆:0.1Cr³⁺ phosphor with a peak at 794 nm and full width at half-maximum (fwhm) of 117 nm was successfully synthesized by introducing Al³⁺ ions. The high performance is reflected in its high internal quantum efficiency (IQE) of 88.06% and good thermal quenching resistance (I_423K = 71.64%). Compared with the initial Cs₂KInF₆:0.1Cr³⁺, the IQE and thermal stability are improved by 16.67% and 72.54%, which stem from the enhanced crystallinity and the strengthened structural rigidity. Finally, a phosphor-converted light-emitting diode (pc-LED) with a superior NIR photoelectric efficiency (21.04%@320 mA) was fabricated. Meanwhile, the pupil tracking, anticounterfeiting, intelligent identification, and bioimaging were successfully demonstrated. This work provides new perspectives for synthesizing efficient NIR fluoride phosphors and designing diverse applications.

All-Inorganic Zero-Dimensional Sb3+-Doped Rb2ScCl5(H2O) Perovskite Single Crystals: Efficient Self-Trapped Exciton Emission and X-ray Detection

Zero-dimensional (0D) halide perovskites have attracted extensive attention for their potential applications in solid-state lighting and X-ray detection due to their fascinating optoelectronic properties and convenient solution processability. Herein, we report the synthesis and photophysical properties of high-quality Sb³⁺-doped 0D Rb₂ScCl₅(H₂O) perovskite single crystals. The pristine crystals exhibit weak yellow self-trapped exciton (STE) emission peaking at 632 nm. The emission quantum yield can be dramatically enhanced from less than 1% to about 53% via Sb³⁺ doping. Spectroscopic characterizations indicate that the photoluminescence enhancement is a result of the efficient energy transfer from Sb³⁺ to the emissive STEs. Additionally, 0.2%Sb³⁺:Rb₂ScCl₅(H₂O) single crystals exhibit potential application in direct X-ray detection with a high sensitivity of 58.5 μC Gy^-1 cm^-2.