Efficient and Thermally Stable Cr3+-activated Germanate Phosphor for Thermometry, Plant Cultivation, and Near-Infrared Light-Emitting Diode Applications

Abstract

In recent years, near-infrared phosphor-converted light-emitting diodes (NIR pc⁃LEDs) have attracted a lot of attention in the fields of night vision, sensing and nondestructive testing. However, realizing multifunctional applications with the same material is still a great challenge. In this study, we prepared an efficient and thermally stable excellent Cr³⁺-activated Cd₃Al₂Ge₃O₁₂ (CAG) garnet NIR phosphor. Under the excitation of 436 nm blue light, its NIR emission covers the range of 600-900 nm, the highest peak is at 714 nm and an internal quantum efficiency is 80.4%. Meanwhile, the phosphor exhibits excellent thermal stability, and the integrated intensity of its NIR emission spectrum at 423 K temperature is 89.4% of room temperature (89.4%@423 K), which shows remarkable high thermal stability characteristics. The temperature-dependent properties of the fluorescence lifetime of Cr³⁺ and the fluorescence intensity ratio of the thermally coupled energy levels in CAG:0.005Cr³⁺ were utilized for thermometry studies from 100 K to 275 K. The relative thermometric sensitivities of the two methods reached a maximum value of 1.4% K^-1 at 200 K and a maximum value of 1.2% K^-1 at 100 K. Finally, the applications of the CAG:0.005Cr³⁺ phosphor in plant illumination, night-vision monitoring and non-destructive testing of biological tissues were discussed by using the synthesized NIR pc⁃LEDs, which proves that the CAG:0.005Cr³⁺ phosphor has a broad application prospect.