White up-conversion luminescence enhancement in Gd2O3: Yb3+-Er3+-Tm3+ phosphor by co-doping Lu3+ ions for high-sensitive temperature sensing

Up-conversion luminescence (UCL) phosphors doped with dual rare-earth (RE) ions emitters have emerged as a focal point of research in the domains of white luminescence and optical temperature sensing. Recent investigations have further highlighted that the local symmetry around the RE ions emitters profoundly influences the UCL efficiency and the sensitivity of optical temperature sensing. Here, Gd₂O₃: Yb³⁺-Er³⁺-Tm³⁺-Lu³⁺ phosphors with different doping concentrations have been successfully synthesized through the CO₂ laser heating melting method. The experimental results reveal that the dual emission centers of Er³⁺ and Tm³⁺ ions significantly enhance the color-tunability of the phosphor. The incorporation of Lu³⁺ ions reducing the local symmetry of the crystal, markedly improves the UCL efficiency and increases the total fluorescence intensity by 2.26 times. Within the temperature range of 298–673 K, a systematic investigation was conducted on the thermal properties of the synthesized phosphors, focusing on the diverse coupling levels—both thermal and non-thermal of Er³⁺ and Tm³⁺ ions. The phosphor doped with 5 %Lu³⁺ ions shows the highest relative sensitivity of 1.26 %K⁻¹, with superior temperature repeatability and resolution. These results offer a novel strategy to optimize the UCL efficiency and temperature measurement performance, making Gd₂O₃: Yb³⁺-Er³⁺-Tm³⁺-Lu³⁺ phosphor an ideal candidate for UCL temperature sensing application.