Upconversion luminescence and favorable temperature sensing performance of eulytite-type Sr(3)Y(PO(4))(3):Yb(3+)/Ln(3+) phosphors (Ln=Ho, Er, Tm)

Phase-pure eulytite-type Sr(3)Y(0.88)(PO(4))(3):0.10Yb(3+),0.02Ln(3+) upconversion (UC) phosphors (Ln = Ho, Er, Tm) were synthesized via 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(3+)), 657 nm red (Ho(3+)) and 476 nm blue (Tm(3+)) 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(3+) doped phosphor has a better overall performance of temperature sensing with thermally coupled (2)H(11/2) and (4)S(3/2) energy levels, whose maximum absolute (S(A)) and relative (S(R)) sensitivities are ~5.07 × 10(−3) K(−1) at 523 K and ~1.16% at 298 K, respectively; (2) the Ho(3+) doped phosphor shows maximum S(A) and S(R) values of ~0.019 K(−1) (298–573 K) and 0.42% at 573 K for the non-thermally coupled energy pairs of (5)F(5)/((5)F(4),(5)S(2)) and (5)I(4)/(5)F(5), respectively; (3) the Tm(3+) doped phosphor has a maximum S(A) of ~12.74 × 10(−3) K(−1) at 573 K for the non-thermally coupled (3)F(2,3)/(1)G(4) energy levels and a maximum S(R) of ~1.74% K(−1) at 298 K for the thermally coupled (3)F(2,3)/(3)H(4) levels. Advantages of the current phosphors in optical temperature sensing were also revealed by comparing with other typical UC phosphors.