Cr³⁺-doped Bi₂Ga₄O₉-Bi₂Al₄O₉ solid-solution phosphors: crystal-field modulation and lifetime-based temperature...

Cr³⁺-doped Bi₂Ga₄O₉-Bi₂Al₄O₉ solid-solution (SS) phosphors were fabricated to explore their possible application in fluorescence lifetime-based temperature sensing. The present samples exhibited E2→A₂4 R-line emissions associated with T₂4→A₂4 phonon sideband emissions of Cr³⁺ in the wavelength range of 600-850 nm upon the excitation of visible light. Through modifying the Al/Ga ratio in the SS hosts, the Cr³⁺ crystal field was easily tuned from intermediate to strong, being beneficial to modulate an energy gap between E2 and T₂4 thermally coupled emitting states. As a result, linearly temperature-sensitive fluorescence lifetime was achieved in the Cr³⁺-doped Bi₂Ga₄O₉-Bi₂Al₄O₉ SSs with a high Al/Ga ratio, enabling us to conveniently and accurately determine a temperature with a high relative sensitivity of 2.13-3.26%  K^-1.