Up-Conversion Luminescence and Optical Temperature-Sensing Properties of Yb³⁺ and Er³⁺ Co-doped Yttrium Aluminum Garnet Phosphor

Fluorescence intensity ratio (FIR) technology is compulsorily needed in non-contact rare-earth luminescent temperature sensors. Here, we present Er/Yb:Y₃Al₅O₁₂ phosphors synthesized via a high-temperature solid-state reaction method. The crystal structure, microstructure, up-conversion luminescence, and energy transfer between the two ions have been comprehensively analyzed. Under 980-nm excitation, the samples exhibited four distinct transition bands at 475 nm, 525 nm, 546 nm, and 664 nm. The quantum efficiency reached 12.14%. Utilizing the thermally coupled level of I₅₂₅/I₅₄₆ as a basis for analysis yields a maximum relative sensitivity of 1.05% K⁻¹. We observed that the spectral color coordinates varied linearly with temperature within a specific range, suggesting its potential application as a means of temperature measurement. Furthermore, employing the non-thermally coupled levels of I₅₄₆/I₄₇₅ for temperature measurement results in an impressive maximum absolute sensitivity of 8.05% K⁻¹, nearly 24 times higher than that achieved through thermally coupled levels alone. The temperature resolution of the synthetic material is basically less than 0.3 K with high thermal stability. Therefore, Er/Yb:Y₃Al₅O₁₂ phosphors hold promise as viable candidates for components in temperature-sensor applications.