A high thermal stability Cr3+-doped gallate far red phosphor for plant lighting: structure, luminescence enhancement and application prospect

Abstract

Cationic substitution is a common material modification strategy. Generally, it follows the principles of radius matching, valency equilibrium and stoichiometric substitution. However, radius-mismatched, nonstoichiometric-ratio ion substitution can achieve unexpected experimental results. Such unexpected results are very important for expanding the research of materials, but the modification mechanism is still unclear. In this work, the optical performance of ZnGa₂O₄:0.02Cr³⁺ (ZGO:0.02Cr³⁺) is effectively regulated by chemical unit cosubstitution (Ge⁴⁺–Li⁺/Na⁺ for Ga³⁺–Zn²⁺) and excess cation substitution synergetic strategies, and the thermal stability is retained at 97.7% at room temperature and 150 °C. Ge⁴⁺–Li⁺ and Ge⁴⁺–Na⁺ replace the lattice position of Ga³⁺–Zn²⁺ to enhance the photoluminescence (PL) intensity and quantum efficiency (QE) of ZGO:0.02Cr³⁺. The optimal doping contents of Ge⁴⁺–Li⁺ and Ge⁴⁺–Na⁺ are all 0.3 mol (PL intensity is 130.3% and 153.4% and QE = 77.4% and 85.1%). With further addition of Li⁺ ions, the emission intensity and QE continued to increase to 176.4% and 83.8%, respectively. The synergistic effect of the mechanism on optical properties is explained via Rietveld refinement, optical band gap energy and thermoluminescence. Finally, LED devices were fabricated by using the ZGO:0.02Cr³⁺,0.03Ge⁴⁺,0.11Li⁺ phosphor to investigate the effect on plant growth. The growth period was reduced and the fruit quality was improved in dwarf potted tomato, which shows the application prospect in plant growth of the ZGO:0.02Cr³⁺ phosphor.