Upconversion luminescence and favorable temperature sensing performance of eulytite-type Sr3Y(PO4)3:Yb3+/Ln3+ phosphors (Ln=Ho, Er, Tm)

Phase-pure eulytite-type Sr3Y0.88(PO4)(3):0.10Yb(3+),0.02Ln(3+) upconversion (UC) phosphors (Ln = Ho, Er, Tm) were synthesized via gel-combustion and subsequent calcination at 1250 degrees 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 (Er3+), 657 nm red (Ho3+) and 476 nm blue (Tm3+) main emissions were analyzed to have average decay times of similar to 52 +/- 2, 260.6 +/- 0.7 and 117 +/- 1 mu s, respectively. It was shown that (1) the Er3+ doped phosphor has a better overall performance of temperature sensing with thermally coupled H-2(11/2) and S-4(3/2) energy levels, whose maximum absolute (S-A) and relative (S-R) sensitivities are similar to 5.07 x 10(-3) K-1 at 523 K and similar to 1.16% at 298 K, respectively; (2) the Ho3+ doped phosphor shows maximum S-A and S-R values of similar to 0.019 K-1 (298-573 K) and 0.42% at 573 K for the non-thermally coupled energy pairs of F-5(5)/(F-5(4),S-5(2)) and I-5(4)/F-5(5), respectively; (3) the Tm3+ doped phosphor has a maximum S-A of similar to 12.74 x 10(-3) K-1 at 573 K for the non-thermally coupled F-3(2,3)/(1)G(4) energy levels and a maximum S-R of similar to 1.74% K-1 at 298 K for the thermally coupled F-3(2,3)/H-3(4) levels. Advantages of the current phosphors in optical temperature sensing were also revealed by comparing with other typical UC phosphors. [GRAPHICS] .