Growth of SnX₂ (X = Br, I) Single Crystals with Self-Trapped Exciton Emission

Broadband emission with a large Stokes shift is important to obtain an excellent color rendering index of the solid-state lighting device. Among low-dimensional material and perovskite-like phosphors with broadband self-trapped emission, Sn-based phosphors have attracted much attention due to their high photoluminescence quantum yield (PLQY). However, the disadvantage is that the synthesis of Sn-based phosphors needs to be performed in a glovebox. Upon photoexcitation, the broadband emission of self-trapped excitons results from exciton-phonon coupling induced by the transient distortion of the lattice. Low-dimensional material structures often promote self-trapped emission because of more vibrational degrees of freedom and easier polarization under photoexcitation. Here, zero-dimensional (0D) SnX₂ (X = Br, I) single crystals are synthesized by the solvent evaporation method in the air. SnX₂ emits blue light, broadband yellow light, and deep red light, among which SnBr₂ has the best luminescence performance. The photoluminescence quantum yield (PLQY) of SnBr₂ reaches 85% and the Stokes shift reaches 265 nm. The PL intensity of SnX₂ is linearly related to excitation power, which preliminarily indicates that the origin of SnX₂ luminescence is attributed to self-trapped emission (STE). The white light-emitting diodes (WLEDs) were fabricated using yellow-emitting SnBr₂ and blue-emitting BaMgAl₁₀O₁₇:Eu²⁺, which has a low correlated color temperature (3160 K) and a relatively common color rendering index (79).