Up-conversion phosphor LaCaGaO4: Er3+/Yb3+ for the optical temperature sensing and anti-counterfeiting

Successfully synthesized LaCaGaO₄: Er³⁺ and LaCaGaO₄: Er³⁺/Yb³⁺ phosphors via high-temperature solid-state reactions and thoroughly investigated their up-conversion luminescence properties under 980 nm and 1550 nm excitation. X-ray diffraction analysis confirmed the phase purity of the materials, and up-conversion luminescence measurements demonstrated emissions in the visible and near-infrared regions, primarily at 530 nm, 550 nm, 670 nm, and 810 nm, corresponding to Er³⁺ transitions. Mechanistic studies revealed that under 980 nm excitation, both green and red emissions are two-photon processes, while under 1550 nm excitation, these emissions are driven by three-photon processes. Co-doping with Yb³⁺ enhanced luminescence intensity, with an increase in the red-to-green emission ratio as the Yb³⁺ concentration increased. Furthermore, these materials exhibited excellent temperature sensing capabilities, with fluorescence intensity ratios from thermally coupled energy levels showing good agreement with the Boltzmann distribution. Maximum sensitivities S_A^MAX of 0.00054 K^-1 (980 nm excitation) and 0.00632 K^-1 (1550 nm excitation) were achieved, highlighting their potential for applications in optical thermometry, color tuning, and anti-counterfeiting.