Synthesis of layered scheelite SrLa2(MoO4)4: Eu3+ red phosphors with high quenching concentration and superior quantum efficiency for improving plant photosynthesis

Abstract

Plant growth light-emitting diodes (LEDs) are gaining more interest in indoor agriculture because they can provide light spectra that better suit the growth needs of crops. Nevertheless, the big challenge of developing red phosphors that exhibit both exceptional thermal stability and high quantum efficiency remains a daunting undertaking. In this work, Eu3+ activated SrLa2(MoO4)4 red phosphors with layered scheelite structure have been successfully developed. When excited with light of 394 nm, these novel phosphors show the strongest emission at 615 nm. Particularly, the addition of NH4Cl flux significantly increased the quantum efficiency of SrLa2(MoO4)4: Eu3+, reaching an impressive 94.5%. In addition, even at a high temperature of 150 °C, the luminescence intensity remained at a remarkable 65.3% in comparison with the room temperature (RT) emission intensity. A red LED device with a photoelectric conversion efficiency of 5.4% and an output power of 35.9 mW at a drive current of 200 mA was prepared by using this red phosphor. Plant photosynthesis study demonstrated that the lotus leaves exposed to red LED lighting for a few weeks had a larger average diameter than those exposed to natural sunlight, which shows that the SrLa2(MoO4)4: Eu3+ phosphor efficiently converts the light provided by LEDs into red light beneficial for plant growth.