Multiwavelength Excitation in Ho 3+ -Doped All-Inorganic Double Perovskites Achieved by Codoping Mn 2+ 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 Ho 3+ -doped Cs 2 NaBiCl 6 microcrystals through a simple hydrothermal method and obtained strong characteristic emissions of Ho 3+ at 492 and 657 nm under low-energy excitation (449 nm). After codoping Mn 2+ , apart from the characteristic emissions from Ho 3+ under 450 nm wavelength excitation, the orangish-red luminescence consisting of the emission band centered at 591 nm from Mn 2+ and a sharp emission peak at 657 nm from Ho 3+ 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 Cs 2 NaBiCl 6 to Mn 2+ and then from Mn 2+ to Ho 3+ . The enhanced absorption efficiency (10.5 → 70.7%) suggests that the codoping of Mn 2+ overcomes the low absorption efficiency caused by f-f forbidden transitions of Ho 3+ . Finally, the diverse luminescent performance within the Cs 2 NaBiCl 6 :Ho 3+ , Mn 2+ phosphor is realized by altering the excitation wavelength, thereby enabling its application in warm-white-light-emitting diodes and plant growth in this work.