Stable double perovskite Cs2AgInCl6 has been reported as a direct gap semiconductor with a wide band gap of 3.23 eV obtained experimentally and 3.33 eV obtained by DFT calculation.

Rational doping and compositional control remain significant challenges in designing luminescent metal halides to achieve highly efficient and tunable emission. Here, the air-stable lead-free Cs 2 InCl 5 •H 2 O crystal with a zero-dimensional structure was investigated as a pristine compound to design new luminescence materials. Sb 3+ -doping in Cs 2 InCl 5 •H 2 O:Sb 3+ enabled broadband yellow emission with a photoluminescence quantum yield up to 95.5%. The emission colors can be expanded into the orange-red region by halogen compositional substitution for Cs 2 InX 5 •H 2 O:Sb 3+ (X = Cl/Br/I). The optical characterizations along with the theoretical calculations demonstrate that the characteristic singlet and triplet self-trapped exciton emissions of ns 2metal-halide centers account for the tunable luminescence. Moreover, the admirable stability against air and heat pave way for its further applications in white light-emitting diodes and high-resolution fluorescent signs in anticounterfeiting technology. Our achievement in the case of Sb 3+ -doped Cs 2 InCl 5 •H 2 O represents a successful strategy for developing stable lead-free metal halides with highly efficient emission for versatile optical applications.

Site preferences of dopant Eu on the locations of K, Ba, and Ca in the mixed cation phosphate KBaCa(PO) (KBCP) are quantitatively analyzed via a combined experimental and theoretical method to develop a blue-emitting phosphor with thermally stable luminescence. Eu ions are located at K2 (M2) and K3 (M3) sites of KBCP, with the latter occupation relatively more stable than the former, corresponding to emissions at 438 and 465 nm, respectively. KBCP:Eu phosphor exhibits highly thermal stable luminescence even up to 200 °C, which is interpreted as due to a balance between thermal ionization and recombination of Eu 5d excited-state centers with the involvement of electrons trapped at crystal defect levels. Our results can initiate more exploration of activator site engineering in phosphors and therefore allow predictive control of photoluminescence tuning and thermally stable luminescence for emerging applications in white LEDs.

The incorporation of impurity ions or doping is a promising method for controlling the electronic and optical properties and the structural stability of halide perovskite nanocrystals (NCs). Herein, we establish relationships between rare‐earth ions doping and intrinsic emission of lead‐free double perovskite Cs2AgInCl6 NCs to impart and tune the optical performances in the visible light region. Tb3+ ions were incorporated into Cs2AgInCl6 NCs and occupied In3+ sites as verified by both crystallographic analyses and first‐principles calculations. Trace amounts of Bi doping endowed the characteristic emission (5D4→7F6‐3) of Tb3+ ions with a new excitation peak at 368 nm rather than the single characteristic excitation at 290 nm of Tb3+. By controlling Tb3+ ions concentration, the emission colors of Bi‐doped Cs2Ag(In1−xTbx)Cl6 NCs could be continuously tuned from green to orange, through the efficient energy‐transfer channel from self‐trapped excitons to Tb3+ ions. Our study provides the salient features of the material design of lead‐free perovskite NCs and to expand their luminescence applications.