Novel rare-earth doped Cs2NaGdCl6:Sb3+ double perovskite nanocrystals toward good ability of color tuning with high quantum efficiency

All-inorganic halide double perovskites have attracted extensive attention as new luminescent materials owing to their high luminous efficiency and wide emission spectrum. In this work, blue-red bicolor Cs2NaGdCl6 (CNGC) double perovskite nanocrystals doped with Sb3+/Ho3+ were prepared using a hydrothermal method. The incorporation of Sb3+ significantly enhanced the intrinsic "self-trapped excitons (STEs)" with a wide-band bright blue emission centered at 470 nm. On this basis, different concentrations of Ho3+ were introduced to achieve color tunable emission from blue to red region, with extremely high quantum efficiencies of 96.53% and 92.17%, respectively. By the use of diverse methods, including spectroscopic analysis and fluorescence lifetime, the mechanism of efficient luminescence related to the different dopant concentrations was comprehensively explored. Results show that Sb3+ not only can enhance the intrinsic STEs luminescence of the CNGC but also has an efficient activation effect on the rare earth ion Ho3+, because it plays the role as a bridge for the two energy transfer channels between the luminescence centers, and the details of the mechanism and energy transfer efficiency were investigated. Thermal stabilities of the double perovskites were studied over the temperature range of 303-473 K and good performances were demonstrated from the fact that the PL intensities of CNGC:1%Sb3+ and CNGC:1%Sb3+/10%Ho3+ at 423 K were 75.1% and 70.1% compared to those at 303 K, respectively. With the CNGC:1%Sb3+ and CNGC:1%Sb3+/10Ho3+ used, the UV light-emitting diode activated devices were fabricated and characterized. The bright blue and red emissions suggest the materials' prominent potential in the application of plant lighting. Finally, to achieve white-light emission in the sole CNGC matrix, a strategy of tri-doping Tb3+ was proposed based on the principle of the three primary colors. The device fabrication with CNGC:1%Sb3+/10%Ho3+/2.5%Tb3+ sample and the characterization processes prove its high feasibility and then provide valuable insights in the design of Sb ion-doped lead-free double perovskites toward easily tunable color in a wide range which can be applied in various fields.