Cr3+-Doped NIR Phosphor with Well-Defined Stokes/Anti-Stokes Phonon Sidebands for a Ratiometric Thermometer and Thermally Stable NIR LEDs

Near-infrared (NIR) luminescent materials have attracted enormous attention for the cutting-edge applications in optical thermometer and NIR LEDs. Herein, we report a highly efficient Cr3+-doped NIR phosphor, BaAl4Sb2O12:0.024Cr3+ (BASO:Cr3+), with 91% internal quantum efficiency. Strikingly, BASO:Cr3+ possesses rare and typical Stokes/anti-Stokes phonon sidebands. The Stokes phonon sideband decreases with increasing temperature, while the anti-Stokes one increases considerably. Consequently, this inverse change has gifted the BASO:Cr3+ with excellent thermal stability, which maintains 118% of the room temperature emission intensity at 423 K. In addition, the well-defined Stokes/anti-Stokes phonon sidebands are applied to a ratiometric thermometer with a maximum relative sensitivity factor of 3.12% K–1 at 150 K. Finally, a well-performing NIR LED is made with BASO:Cr3+, which can be used for nondestructive testing, information encryption, and night vision. Our findings not only shed light on the emission behavior of Cr3+ but also point out an avenue for thermally stable NIR phosphors and a sensitive optical thermometer.