Upconversion luminescence of Sr8MgY(PO4)7:Yb3+–Er3+/Ho3+ phosphors for optical thermometry

In this work, to develop new upconversion (UC) luminescent material for optical thermometry, the Sr8MgY(PO4)7:Yb3+–Er3+/Ho3+ phosphors were explored, and their UC luminescence properties upon 980 nm excitation were investigated. The phase purity of the samples was checked by XRD patterns, which showed no secondary phase existed. For Yb3+–Er3+ codoped samples, three peaks including two green and one red emissions have been found, and the optimal Er3+ doping content was determined to be 3 mol% with regard to the green emissions. For Yb3+–Ho3+ codoped samples, the green and red emissions demonstrated different change with Ho3+ concentration, which could be owing to the cross-relaxation in Ho3+ ions. By studying the temperature-dependence of the emission intensities, it was suggested that several strategies can be used for temperature sensing, involving the I521/I548 and I660/I521 of Er3+ and I658/I548 of Ho3+. The absolute and relative sensitivities were evaluated and the Yb3+–Ho3+ codoped sample showed the higher sensitivities than Yb3+–Er3+ codoped sample. The above results indicated the present phosphors could be candidate luminescent materials for optical thermometry.