The development of ultrafast scintillators is critical to the GHz X-ray and time-of-flight (TOF) imaging techniques. Low-dimensional silver-based halides have emerged as promising candidates due to high radioluminescence efficiency and ultrafast decay time. However, the ultrafast scintillation mechanism in silver-based halides, such as Rb 2 AgBr 3 (RAB), remains controversial. Here, the study reveals the origin of ultrafast scintillation timing response in melt-grown RAB bulk crystals. The RAB shows light-yellow emission with a photoluminescence quantum yield (PLQY) of 13.9%. Under the picosecond (ps) pulse X-ray irradiation, RAB has an ultrafast decay time of 3.2 ns that accounts for 40.5% of the total emitted light. The light yield is estimated as 3100 photons MeV −1 under 22 Na irradiation. Based on the temperature-dependent radioluminescence (RL) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and spectrally resolved thermally-stimulated luminescence (TSL) glow curves, it is confirmed that the bromine vacancy as the F-center is the origin of the ultrafast scintillation component. These findings provide elaborated and fundamental insights into the ultrafast luminescent mechanisms of low-dimensional silver-based halides, thereby opening up new design horizons in the development of ultrafast scintillators.
Photochromic materials have shown significant potential in a plethora of possible applications. However, in practical applications, they remain limited by intricate multi-stage synthesis processes and a restricted range of photochromic colors. Modulating the chromatic properties involves an intricate manipulation of their chemical composition, crystal structure, and trapping energy levels, rendering it extremely challenging to achieve a desired color gamut. In this study, apatite-type materials are rapidly synthesized using a microwave-assisted approach. The photochromic behavior is systematically examined by substituting F⁻ ions with Cl⁻ ions, facilitating the transformation of color centers from pink to green and ultimately to blue. Notably, the prominent reflectance absorption peak ≈554 nm exhibited a gradual red shift to 625 nm. A thorough characterization reveals that this large shift in wavelength of F-center arises from the effective modulation in the trapping energy levels with differing trap distributions linked to photochromism observed across the various Sr₅(PO₄)₃F₁₋ x Cl x :1%Eu. Finally, the potential applications of these multicolor compounds are demonstrated in routine chromatic decorations and sophisticated multi-hued cryptographic technologies. These findings highlight the efficacy of trapping energy management in optimizing photochromic behavior and the considerable capability of the photochromic materials for on-demand practical applications.
Photon-driven chemical processes are usually mediated by oxides, nitrides and sulfides whose photo-conversion efficiency is limited by charge carrier recombination. Here we show that lithium hydride undergoes photolysis upon ultraviolet illumination to yield long-lived photon-generated electrons residing in hydrogen vacancies, known as F centres. We demonstrate that photon-driven dehydrogenation and dark rehydrogenation over lithium hydride can be fulfilled reversibly at room temperature, which is about 600 K lower than the corresponding thermal process. As light-driven F centre generation could provide an alternative approach to charge carrier separation to favour chemical transformations that are kinetically or thermodynamically challenging, we show that light-activated lithium hydride cleaves the N≡N triple bond to form a N–H bond under mild conditions. Co-feeding a N 2 /H 2 mixture with low H 2 partial pressure leads to photocatalytic ammonia formation at near ambient conditions. This work provides insights into the development of advanced materials and processes for light harvesting and conversion.
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