Energy-Transfer-Enhanced Cr³⁺/Ni²⁺ Co-doped Broadband Near-Infrared Phosphor for Fluorescence Thermometers and Near-Infrared Window Imaging

Here, near-infrared broad dual-band emission phosphors were achieved through energy transfer between Cr³⁺ and Ni²⁺ ions in the β-Ga₂O₃ host. All samples co-doped with Cr³⁺ and Ni²⁺ exhibit dual-band emission covering 600-1700 nm under 430 nm excitation. Thanks to the doping of Cr³⁺ ions, the emission intensity of Ga₂O₃:Cr³⁺, Ni²⁺ phosphors has increased by about 2.4 times and the internal quantum efficiency has increased by 83.2% compared to Ga₂O₃:Ni²⁺ phosphors. Meanwhile, when the fluorescence lifetime was monitored at 745 nm, an efficient energy transfer between Cr³⁺ and Ni²⁺ ions in the β-Ga₂O₃ host was verified. Due to the significant differences in the emission temperature-sensitive properties of Cr³⁺ and Ni²⁺ ions, a thermometer was designed utilizing fluorescence intensity ratio technology, achieving a maximum relative sensitivity of 5.26% K^-1, which surpasses most optical temperature measurement phosphors. This suggests that Ga₂O₃:Cr³⁺, Ni²⁺ samples hold promise as potential candidates for optical thermometer materials. Additionally, the broadband near-infrared emission of the Ga₂O₃:Cr³⁺, Ni²⁺ sample has been investigated for potential applications in component analysis and night vision, demonstrating its versatility for multifunctional applications.