Efficient and thermally stable Cr3+-activated germanate phosphor for thermometry, plant cultivation, and near-infrared light-emitting diode applications

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 Cr 3+ -activated Cd 3 Al 2 Ge 3 O 12 (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 Cr 3+ and the fluorescence intensity ratio of the thermally coupled energy levels in CAG:0.005Cr 3+ 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:0.005Cr 3+ 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:0.005Cr 3+ phosphor has a broad application prospect.