Upconversion thermal enhancement of ²H_11/2→⁴I_15/2 of Er³⁺ and blue emission of impurity Tm³⁺ in Sr₃(PO₄)₂:Er³⁺/Yb³⁺

Abstract

A series of Sr 2.99-x (PO 4 ) 2 :.01Er 3+ /xYb 3+ (x = .02, .04, .06, .08, .10) phosphors in the presence of impurity Tm 3+ were synthesized by high temperature solid-state method, and X-ray diffraction results show that these samples are pure R-3 m(166) space group phase. The upconversion luminescence (UCL) of Er 3+ and impurity Tm 3+ under 980-nm laser excitation were investigated, and the results show that the intense blue UCL of impurity Tm 3+ and thermal enhancement of 2 H 11/2 → 4 I 15/2 of Er 3+ simultaneously exist. When Er 3+ doping concentration is kept at .01, both the blue UCL intensity of impurity Tm 3+ and green and red UCL intensity of Er 3+ reach the maximum at Yb 3+ doping concentration of .08. The thermal enhancement effect of 2 H 11/2 → 4 I 15/2 of Er 3+ was observed as high as 3.27 times from 303 to 723 K, which is because of lattice distortion and phonon-assisted transition. In addition, the optical temperature performance of Sr 2.91 (PO 4 ) 2 :.01Er 3+ /.08Yb 3+ sample was studied, and the maximum absolute temperature sensitivity was calculated as .00623 K −1 at 538 K. This study suggests that Sr 3 (PO 4 ) 2 :Er 3+ /Yb 3+ phosphors in the presence of impurity Tm 3+ have a promising application prospect as optical temperature sensor at high temperature.