Energy-Transfer-Enhanced\nCr<sup>3+</sup>/Ni<sup>2+</sup> Co-doped Broadband Near-Infrared Phosphor\nfor Fluorescence Thermometers\nand Near-Infrared Window Imaging

Here, near-infrared broad dual-band emission phosphors\nwere achieved\nthrough energy transfer between Cr<sup>3+</sup> and Ni<sup>2+</sup> ions in the β-Ga<sub>2</sub>O<sub>3</sub> host. All samples\nco-doped with Cr<sup>3+</sup> and Ni<sup>2+</sup> exhibit dual-band\nemission covering 600–1700 nm under 430 nm excitation. Thanks\nto the doping of Cr<sup>3+</sup> ions, the emission intensity of Ga<sub>2</sub>O<sub>3</sub>:Cr<sup>3+</sup>, Ni<sup>2+</sup> phosphors has\nincreased by about 2.4 times and the internal quantum efficiency has\nincreased by 83.2% compared to Ga<sub>2</sub>O<sub>3</sub>:Ni<sup>2+</sup> phosphors. Meanwhile, when the fluorescence lifetime was\nmonitored at 745 nm, an efficient energy transfer between Cr<sup>3+</sup> and Ni<sup>2+</sup> ions in the β-Ga<sub>2</sub>O<sub>3</sub> host was verified. Due to the significant differences in the emission\ntemperature-sensitive properties of Cr<sup>3+</sup> and Ni<sup>2+</sup> ions, a thermometer was designed utilizing fluorescence intensity\nratio technology, achieving a maximum relative sensitivity of 5.26%\nK<sup>–1</sup>, which surpasses most optical temperature measurement\nphosphors. This suggests that Ga<sub>2</sub>O<sub>3</sub>:Cr<sup>3+</sup>, Ni<sup>2+</sup> samples hold promise as potential candidates for\noptical thermometer materials. Additionally, the broadband near-infrared\nemission of the Ga<sub>2</sub>O<sub>3</sub>:Cr<sup>3+</sup>, Ni<sup>2+</sup> sample has been investigated for potential applications\nin component analysis and night vision, demonstrating its versatility\nfor multifunctional applications.