We report the growth of a halide-based double perovskite, Cs 2 Na x Ag 1Àx InCl 6 :y%Mn, via a facile hydrothermal reaction at 180 8C. Through a co-doping strategy of both Na + and Mn 2+ , the as-prepared crystals exhibited a red afterglow featuring a high color purity (ca. 100 %) and a long duration time (> 5400 s), three orders of magnitude longer than those solution-processed organic afterglow crystals. The energy transfer (ET) process between self-trapped excitons (STE) and activators was investigated through time-resolved spectroscopy, which suggested an ET efficiency up to 41 %. Importantly, the nominal concentration of dopants, especially in the case of Na + , was found a useful tool to control both energy level and number distribution of traps. Cryogenic afterglow measurements suggested that the afterglow phenomenon was likely governed by thermal-activated exciton diffusion and electron tunneling process.

Near‐infrared (NIR) afterglow is keenly sought in emerging areas including deep‐tissue imaging and night‐vision surveillance, while only few successes in powder phosphors are achieved through solid‐state calcination. In this work, a perovskite single crystal, namely Cs2Na0.2Ag0.8InCl6:Yb3+, is grown in solution via a simple hydrothermal reaction. Through a co‐doping strategy involving both Na+ and Yb3+, dual‐band emission in the visible and NIR region is activated by self‐trapped excitons (STE) and lanthanide ions, respectively. Importantly, the total photoluminescence quantum yield (PL QY) of both bands is boosted to ≈82%. Intriguingly, a long‐lasting afterglow at the NIR band (≈7200 s) and a simultaneous photochromism is observed after ceasing the excitation. Importantly, the transparency of crystals exhibit a pronounced contrast in the decoloration process, enabling a quantitative analysis of photochromism at varied temperatures. On the other hand, the transparent crystals enable the design of a light‐storage battery free of reabsorption, featuring a linear power output with crystal loading. This work proposes a new paradigm to quantitatively correlate the afterglow traps to photochromism, opening many possibilities to practical applications of NIR‐afterglow transparent crystals.

Despite their low toxicity and phase stability, lead-free double perovskite nanocrystals, Cs2AgInCl6 in specific, have suffered from low quantum yield of photoluminescence. This is mainly due to two reasons, including (i) the quenching effect from metal silver which was usually formed at high temperature from Ag+ reduction in the presence of organic amines and (ii) the parity-forbidden transition of pristine double perovskites. Here, we reported a room-temperature synthesis of Cs2AgInCl6 nanocrystals in an inverse microemulsion system, where Ag+ reduction was largely suppressed. By codoping Bi and Na ions, dark self-trapping excitons (STEs) were converted into bright ones, enabling a bright phosphor of photoluminescence quantum yield up to 56%. Importantly, the doping approach at room temperature relaxed the parity-forbidden transition (1S0 → 3P2) of Bi-6s2 orbitals, revealing a fine structure of a triband excitation profile. Such spin-rule relaxation was ascribed to symmetry breaking of the doped lattice, which was evidenced by Raman spectroscopy. In a proof-of-concept experiment, the bright nanocrystals were used as a color-converting ink, which enabled a stable white light light-emitting diode to operate in various environments, even under water, for long-term service.

The red emission of Cs4PbI6 zero-dimensional perovskite is found heterogeneous between individual particles, yet exhibits an enhanced stability towards both anion exchange reaction and photo radiation than CsPbI3.

No abstract

The photoluminescence of green-emitting Cs 4 PbBr 6 crystals has shown superior stability over that of the standard CsPbBr 3 phase toward many harsh conditions, including long-term storage, heat shock, light irradiation, and even multiple solvent rinsing. However, the understanding of its origin remained controversial, partially due to the lack of real-time observation on its initial formation stage. Here, this work reported the direct observation of emitter generation in the crystallization stage. Through the use of a home-made crystal incubator coupled with a fluorescent microscope, both the crystal growth and emitter emergence were tracked in a real-time manner. The emitter distribution was found oriented along the c axis and the cooling rate of the precursor was found as a key factor to manipulate the emitter density, which was reported for the first time to the best of our knowledge. Through an ultraslow cooling procedure, a full-body emitting crystal of high photoluminescence quantum yield (PL QY) up to 83% was obtained. The emitter emergence was accompanied with a release of strain as evidenced by Williamson−Hall fitting, and the PL evolution was further simulated with the Johnson−Mehl−Avrami model. Combined with the linear relationship of lifetime to temperature, a two-dimensional phase of disordered Cs n+1 Pb n Br 3n+1 was proposed as the emitter according to the Rosales model. Although the direct evidence of the emitter phase remains elusive, this work provided many new insights into the PL origin of Cs 4 PbBr 6 .

Nanocrystal (NC) form of zero-dimensional perovskite (Cs4PbBr6) has spurred a great deal of attention due to both its elusive green emission and phase-pure nature, which posed a major challenge to...

We report the growth of a halide-based double perovskite, Cs 2 Na x Ag 1Àx InCl 6 :y%Mn, via a facile hydrothermal reaction at 180 8C. Through a co-doping strategy of both Na + and Mn 2+ , the as-prepared crystals exhibited a red afterglow featuring a high color purity (ca. 100 %) and a long duration time (> 5400 s), three orders of magnitude longer than those solution-processed organic afterglow crystals. The energy transfer (ET) process between self-trapped excitons (STE) and activators was investigated through time-resolved spectroscopy, which suggested an ET efficiency up to 41 %. Importantly, the nominal concentration of dopants, especially in the case of Na + , was found a useful tool to control both energy level and number distribution of traps. Cryogenic afterglow measurements suggested that the afterglow phenomenon was likely governed by thermal-activated exciton diffusion and electron tunneling process.