Enhanced Thermal Stability in Eu ³⁺ -Doped Phosphors by Red-Shifting the Charge Transfer Band

The antithermal quenching behavior of phosphors exhibiting a charge transfer band (CTB) red-shift has drawn interest for solid-state lighting and optical sensing. However, controlling the red-shift magnitude to improve thermal stability in Eu³⁺-doped phosphors remains challenging. This work addresses this by tuning the P/V ion concentration (<i>x</i> = 0-1). It is found that at low vanadium content (<i>x</i> ≤ 0.25), the red-shift is governed by thermal population of the (VO₄)^3- groups vibrational levels, while at higher concentrations (<i>x</i> ≥ 0.5), a marked decrease in CTB energy becomes dominant. This approach greatly enhances thermal stability, and the emission intensity at 573 K is 13.77 times higher than that at 298 K (<i>x</i> = 1). Furthermore, a single-band ratio thermometry model based on the red-shift achieves a high relative sensitivity of 5.023% K^-1 at 298 K, offering a new strategy for designing high-performance optical temperature sensing materials.