Upconversion luminescence and favorable temperature sensing performance of eulytite-type SrY(PO):Yb/Ln phosphors (Ln=Ho, Er, Tm).

Phase-pure eulytite-type SrY(PO):0.10Yb,0.02Ln upconversion (UC) phosphors (Ln = Ho, Er, Tm) were synthesized gel-combustion and subsequent calcination at 1250°C. Their UC luminescence, temperature-dependent fluorescence intensity ratio of thermally and/or non-thermally coupled energy levels, and performance of optical temperature sensing were systematically investigated. The phosphors typically exhibit green, orange-red and blue luminescence under 978 nm NIR laser excitation for Ln = Er, Ho and Tm, respectively, which were discussed from two- and three-photon processes. The 524 nm green (Er), 657 nm red (Ho) and 476 nm blue (Tm) main emissions were analyzed to have average decay times of ~52 ± 2, 260.6 ± 0.7 and 117 ± 1 μs, respectively. It was shown that (1) the Er doped phosphor has a better overall performance of temperature sensing with thermally coupled H and S energy levels, whose maximum absolute ( ) and relative ( ) sensitivities are ~5.07 × 10 K at 523 K and ~1.16% at 298 K, respectively; (2) the Ho doped phosphor shows maximum and values of ~0.019 K (298-573 K) and 0.42% at 573 K for the non-thermally coupled energy pairs of F/(F,S) and I/F, respectively; (3) the Tm doped phosphor has a maximum of ~12.74 × 10 K at 573 K for the non-thermally coupled F/G energy levels and a maximum of ~1.74% K at 298 K for the thermally coupled F/H levels. Advantages of the current phosphors in optical temperature sensing were also revealed by comparing with other typical UC phosphors.