Obtaining versatile Cr3+-activated phosphors with improved far-red emissions via host composition modulation

Abstract

Cr3+-activated spinel-type phosphors have great potential in different application scenes due to their unique sharp and far-red (FR) emission. However, the multi-functionalization of these phosphors is still limited by their unsatisfied comprehensive properties. Herein, a simple composition engineering was used to explore versatile phosphors, using Ga3+ to substitute Al3+ to improve the optical performances of spinel LiAl5–xGaxO8:Cr3+. The substitution of Ga3+ evidently affects the crystal field environment of Cr3+ and further accounts for the luminescence optimization. Using the optimized phosphor, two sensitive thermometers based on fluorescence intensity ratio (FIR) technique were explored on account of the different temperature dependencies of 4T2→4A2 and 2E→4A2 emission and of R2 and R1 emission. The maximum relative sensitivity Sr are 1.29%/K at 323 K and 1.94%/K at 298 K, respectively, which are superior to that of the Ga3+-unsubstituted one. Besides, the Ga3+→Al3+ substitutions endow the resultant phosphors with larger atomic number (Zeff) and theoretical density, which is more conducive to improving X-ray-stimulated emission for X-ray detection. Finally, the potential applications of the developed phosphor are also reflected in plant growth and night vision surveillance, as it is shown to be capable of matching with the absorption of phytochrome PFR and visualizing objects in the dark. This contribution not only proves that the developed LiAl5–xGaxO8:Cr3+ FR phosphors are promising versatile platforms, but also provides an essential guidance for designing more novel multi-functional materials.