Upconversion Yb3+/Er3+:La2Ti2O7 phosphors for solid-state lighting and optical thermometry

The solid-state reaction was employed as a suitable method to produce orthorhombic Yb3+/Er3+ co-doped La2Ti2O7 phosphors. The pump power and temperature dependencies of spectra of the Yb3+/Er3+ co-doped La2Ti2O7 were studied for color tunability and optical thermometry.The pump power significantly affected the color coordinates of the phosphors. The upconversion green light transformed to the broad white light at higher pump power. A two-photon transition was proposed to explain the upconversion energy transfer process. The fluorescence intensity ratio technique was used to calculate the optical temperature sensor sensitivities. The ΔE energy difference obtained from the intensity ratios of the thermally coupled 2H11/2 and 4I15/2 energy levels of Er3+ are 763.64 ± 76.62 cm−1, 777.77 ± 44.62 cm−1, 640.71 ± 137.39 cm−1 for La1.95Yb0.04Er0.01Ti2O7, La1.94Yb0.04Er0.02Ti2O7, and La1.93Yb0.04Er0.03Ti2O7, respectively. Absolute temperature sensitivities of the phosphors decreased with increasing Er3+ concentration. The maximum absolute sensitivity was determined to be 0.51x10-2 K−1 at 553 K for La1.95Yb0.04Er0.01Ti2O7, 0.64x10-2 K−1 at 571 K for La1.94Yb0.04Er0.02Ti2O7, and 0.38x10-2 K−1 at 457 K for La1.93Yb0.04Er0.03Ti2O7.