properties, low cost, facile preparation and high defect tolerance. [1] Remarkable progress has been made, especially in terms of widespread applications spanning from solar cells, photodetectors, photocatalysts, and solid-state lasers to light-emitting diodes (LEDs). [2] In more recent years, owing to the exceptional luminescence properties, such as high brightness, color tunability, and intense absorption coefficient, lead halide perovskites have found promising potential applications as color converter for next-generation solid-state lightings and backlight displays. [3] Unfortunately, the intrinsic nature of poor stability and toxicity of lead halide perovskites are some serious issues to be tackled if the materials are to be used on a large scale. The chemical instability will severely restrict the lifespan of devices, and the accumulation of lead will cause serious environmental problems and fatal threat to human health. [4] Extensive efforts have been devoted to overcome the thorny challenges on the way to practical applications. To completely eliminate the potential danger of lead leakage, the simplest and practicable way is to replace it in the B site of ABX 3 with nontoxic isovalent metal ions. [5] As reasonable candidates, Ge 2+ and Sn 2+ ions are the first to come to mind for the substitution of Pb 2+ due to the same electronic configuration of ns 2 np 0 Lead halide perovskites have emerged as superstar semiconductors owing to their superior optoelectronic properties. However, the issues of chemical and thermodynamic instability and toxicity are yet to be resolved. Here, the non-and Bi 3+-doped all-inorganic lead-free perovskite derivatives are reported. Most remarkable is the successful extending of excitation of Cs 2 ZrCl 6 to match with the commercial near ultraviolet light-emitting diode chips via deliberate Bi 3+ aliovalent doping. The blue emission, contrary to self-trapped exciton (STE) emissions amply reported previously, originates from Bi 3+ ionoluminescence with a high photoluminescence quantum efficiency of 50%. The competition for harvesting electrons between STEs and Bi 3+ is studied in detail by steady-and transient-state fluorescence spectroscopy in combination with theoretical calculations. Surface grafting endows Cs 2 ZrCl 6 :Bi 3+ with a robust water-resistant core-shell-like structure and abiding emission. Surprisingly, the emission intensity even increases to 115.94% of the initial level after immersing in water for 2 h. The as-obtained phosphor enables the fabrication of a white light-emitting diode (w-LED), achieving CCT = 4179 K and Ra = 81.9. This work not only promotes the step toward development of leadfree, stable, and high-efficiency perovskite derivatives for the next-generation warm w-LEDs, but also reveals the structure-PL relationship.

In the current "big data" era, the state-of-theart optical data storage (ODS) has become a front-runner in the competing data storage technologies. As one of the most promising methods for breaking the physical limitation suffered by traditional ones, the advance of optically stimulated luminescence (OSL) based optical storage technique is now still limited by the simultaneous singlelevel write-in and readout in a same spot. In this work, to bridge the data-capacity gap, we report for the first time a novel and promising nonphysical multidimensional OSLbased ODS flexible medium for erasable multilevel optical data recording and reading. We tailor multidimensional traps with discrete, narrowly distributed energy levels through (multi-)codoping of selective trivalent rare-earth ions into Eu 2+ -activated barium orthosilicate (Ba 2 SiO 4 ). Upon UV/blue light illumination, information can be sequentially recorded in different traps assisted by thermal cleaning with an increase of storage capacity by orders of magnitude, which is addressable individually in the whole domain or bit-by-bit mode without the crosstalk by designed thermal/optical stimuli. Remarkably, good data retention and robust fatigue resistance have been achieved in recycle data recording. Insight is forged from charge carrier dynamics and interactions with traps for a universal method of data storage, and proof-of-concept applications are also demonstrated, thereby providing the way to not only rewritable multilevel ODS but also high-security encryption/decryption.

The use of noninvasive and rapid responsive spectroscopy coupled to potential applications under harsh conditions has led to an increased interest in all-optical ratiometric thermometers. In this work, we report on a novel all-optical ratiometric thermometer made of Ca8BaCe­(PO4)7:Mn2+, trap-mediated red emission of Mn2+ displayed antithermal quenching in the room-temperature (RT)–573 K range for a Mn2+ content of 0.05. The blue emission of Ce3+ weakens rapidly at elevated temperature, thereby leading to an increased discriminability of fluorescence intensity and a good temperature sensitivity. The maximum fluorescence and lifetime-based relative sensitivity are ∼2.17% K–1 and 5.14% K–1. The insight of interplay among diverse emission centers and traps is revealed. Moreover, the color of the emissions changes between yellow and red with temperature variations when Eu2+ ions are doped into Ca8BaCe­(PO4)7:Mn2+. The highly sensitive self-calibrated optical thermometer shows great promise with safety anticounterfeiting applications.

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Non-lead metal halide double perovskites (MHDP), recognized as one of the most promising alternatives to the lead-based metal halide perovskites (MHP), have received enormous attention in recent years due to...

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Photochromism modification by trap engineering via rare earth ion co-dopants for erasable optical data storage.