Effects of optically inert ions on up-conversion luminescence and temperature-sensing properties of Y2O2S: Er3+/Yb3+/Tm3+ phosphors

The quenching of luminescence in Er 3+ /Yb 3+ co-doped with Tm 3+ presents a dilemma as it substantially diminishes thermometric performance. In this study, Y 2 O 2 S: Er 3+ /Yb 3+ /Tm 3+ phosphors were synthesized using a homogeneous precipitation method combined with a sulfurization process. In addition, three sets of fluorescence intensity ratio (FIR) models were designed, which have self-calibration function. The effects of incorporation of Li + or Li + /Ba 2+ on the up-conversion luminescence (UCL) intensity and thermometric performance of the phosphors were systematically studied. The results show that the introduction of Li + or Li + /Ba 2+ co-doping leads to lattice distortion and the formation of oxygen ion vacancies in the lattice, which further accelerates the energy transfer process and mixes the charge transfer states , and ultimately dramatically improves the UCL and thermometric performance. The introduction of Li + and Li + /Ba 2+ co-doping enhanced the UCL of the materials by about 3.7 times and 5.6 times compared to Y 2 O 2 S: Er 3+ /Yb 3+ /Tm 3+ . When based on nonthermally coupled levels (NTCLs), the S r-max of Li + /Ba 2+ co-doped sample is 0.080 K −1 at 573 K, which is 87 % higher than that based on TCLs. These findings not only provide a new avenue for improving the UCL and thermometric performance but also provide an accurate self-calibration FIR model over a wide temperature range.