Multiwavelength Excitation in Ho3+-Doped All-Inorganic Double Perovskites Achieved by Codoping Mn2+ for Warm-White LEDs and Plant Growth

Doping lanthanide ions is an efficient method to modify the optical properties of lead-free double-perovskite halides. However, most lanthanide-doped double perovskites show a low luminescence efficiency and require a high excitation energy. Here, we have successfully prepared a series of Ho3+-doped Cs2NaBiCl6 microcrystals through a simple hydrothermal method and obtained strong characteristic emissions of Ho3+ at 492 and 657 nm under low-energy excitation (449 nm). After codoping Mn2+, apart from the characteristic emissions from Ho3+ under 450 nm wavelength excitation, the orangish-red luminescence consisting of the emission band centered at 591 nm from Mn2+ and a sharp emission peak at 657 nm from Ho3+ is obtained under 355 nm UV light excitation. Photoluminescence (PL) emission and excitation spectra, along with the PL decay curves, confirm the existence of an energy-transfer channel from Cs2NaBiCl6 to Mn2+ and then from Mn2+ to Ho3+. The enhanced absorption efficiency (10.5 → 70.7%) suggests that the codoping of Mn2+ overcomes the low absorption efficiency caused by f–f forbidden transitions of Ho3+. Finally, the diverse luminescent performance within the Cs2NaBiCl6:Ho3+, Mn2+ phosphor is realized by altering the excitation wavelength, thereby enabling its application in warm-white-light-emitting diodes and plant growth in this work.