Cr^3+-doped Bi_2Ga_4O_9-Bi_2Al_4O_9 solid-solution phosphors: crystal-field modulation and lifetime-based temperature sensing

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.