Anti-thermal-quenching in Zn1-Li Ga2O4-δ:Cr3+ phosphor for plant cultivation and optical thermometer based on defect engineering

Excellent thermal stability and appropriate broadband emission of deep red phosphors are indispensable for high-power plant cultivation light emitting diodes. Herein, an anti-thermal-quenching phosphor Zn1-xLixGa2O4-δ:Cr3+ was reported and the defects were introduced into the lattice to enhance the thermal stability via unequal doping. For the representative Zn0.85Li0.15Ga2O4-δ:Cr3+, the emission spectral profile was broadened as two additional emission peaks at around 630 and 675 nm appeared at high temperature and anti-thermal-quenching was observed. Interestingly, [GaO4] tetrahedron and [ZnO6] octahedron appeared as inverted defect and this structure was proved to be partially inverse spinel-structure at high temperature. This anti-thermal behaviour is mainly ascribed to the phase transition between spinel and inverse spinel at high temperature. The emission spectrum of Zn0.85Li0.15Ga2O4-δ:Cr3+ at 423 K agreed well with the absorption peaks of phytochromes. The relative sensitivity of the phosphor was carried out to explore the application in optical thermometer. This simple strategy to create defects opens a new insight to design anti-thermal-quenching phosphors for high-power LEDs and optical thermometer applications.