Multimode Luminescence Tailoring and Improvement of Cs NaHoCl Cryolite Crystals via Sb /Yb Alloying for Versatile Photoelectric Applications.

Lead-free halide double perovskites are currently gaining significant attention owing to their exceptional environmental friendliness, structural adjustability as well as self-trapped exciton emission. However, stable and efficient double perovskite with multimode luminescence and tunable spectra are still urgently needed for multifunctional photoelectric application. Herein, holmium based cryolite materials (Cs NaHoCl ) with anti-thermal quenching and multimode photoluminescence were successfully synthesized. By the further alloying of Sb (s-p transitions) and Yb (f-f transitions) ions, its luminescence properties can be well modulated, originating from tailoring band gap structure and enriching electron transition channels. Upon Sb substitution in Cs NaHoCl , additional absorption peaking at 334 nm results in the tremendous increase of photoluminescence quantum yield (PLQY). Meanwhile, not only the typical NIR emission around 980 nm of Ho is enhanced, but also the red and NIR emissions show a diverse range of anti-thermal quenching photoluminescence behaviors. Furthermore, through designing Yb doping, the up-conversion photoluminescence can be triggered by changing excitation laser power density (yellow-to-orange) and Yb doping concentration (red-to-green). Through a combined experimental-theoretical approach, the related luminescence mechanism is revealed. In general, by alloying Sb /Yb in Cs NaHoCl , abundant energy level ladders are constructed and more luminescence modes are derived, demonstrating great potential in multifunctional photoelectric applications.