Precise site occupation of Zn2+ in Rb2CuBr3 to regulate exciton recombination for violet luminescence

Abstract

With its tunable bandgap and 385 nm violet emission, Rb₂CuBr₃ is a promising candidate for violet light-emitting diodes (LEDs). This work shows how Zn²⁺ doping enhances self-trapped exciton (STE) emission by modulating excited-state dynamics, covering key factors in STE luminescence dynamics. An antisolvent synthesis strategy is developed to achieve Rb₂CuBr₃:xZn²⁺. The lowest defect formation energy (Eform) confirmed Zn²⁺ occupation for the Cu⁺ site. X-ray absorption fine structure (XAFS) revealed that the shortened bond lengths arising from stronger Zn–Br interactions induced lattice contraction and narrowed the band gap, thereby favoring the violet luminescence. Low-temperature-dependent photoluminescence (TDPL) spectra and time-resolved fluorescence (TRF) spectra further elucidated the overall STE dynamics. The increased exciton binding energy (E_b) by 37% effectively suppressed exciton thermal dissociation to form a classical STE process. However, the suppression ratio of the nonradiative to radiative recombination rate (k_nr/k_r) is 56.7%. Notably, the nonradiative recombination is depressed extensively. The optimized doping at Rb₂CuBr₃:0.3Zn²⁺ results in a maximum photoluminescence quantum yield (PLQY) of 70.6% and an approximate twofold enhancement in PL intensity. This work shows how Zn²⁺ doping enhances STE emission by modulating excited-state dynamics. The fabricated violet LED integrates the function of efficient curing, exhibiting broad application prospects.