Sb³⁺/Ln³⁺ Co-Doping Enables Color-Tunable and High-Efficiency White-Light Emission in Cs₂NaYCl₆ Double Perovskite Microcrystals

In this study, a series of single-, double-, and triple-doped rare-earth halide double perovskite microcrystals, specifically Sb3+- and Ln3+-doped (Ln3+ = Er3+, Ho3+) Cs2NaYCl6, were successfully synthesized via a solvothermal method. In Cs2NaYCl6:Sb3+ microcrystals, the incorporation of Sb3+ ions effectively relaxes the parity-forbidden transitions, resulting in a substantial enhancement of the photoluminescence quantum yield (PLQY) from 11.15 to 77.55%, along with prominent blue emission. Moreover, codoping with Er3+ and Ho3+ ions enables a continuous color transition, driven by efficient energy transfer between self-trapped excitons (STEs) and the rare-earth dopants. This leads to a progressive shift from blue (STEs) to green (Er3+) and ultimately to red (Ho3+) emission. Such remarkable color tunability facilitates the creation of a single-source white-light phosphor, achieving well-defined CIE chromaticity coordinates of (0.3482, 0.2894) and a stable correlated color temperature (CCT) of 4531 K. Notably, the emission spectrum closely approximates ideal white light, highlighting its significant potential for optoelectronic applications, particularly in white-light-emitting diodes (WLEDs). The codoping strategy with Sb3+ and rare-earth ions not only enhances luminescence efficiency but also advances the development of high-performance, environmentally friendly phosphor materials, paving the way for next-generation optoelectronic devices.