Upconversion luminescence of Ba9Y2Si6O24:Yb3+-Ln3+ (Ln = Er, Ho, and Tm) phosphors for temperature sensing

To develop new phosphor materials for optically thermal sensing, the Yb3+-Er3+, Yb3+-Ho3+ and Yb3+-Tm3+ doped Ba9Y2Si6O24 samples were prepared by the solid-state reaction method, and the orange-yellow, green and blue emissions for upconversion luminescence have been obtained, respectively. The phase composition of the samples was characterized by X-ray diffraction, indicating the pre-prepared phosphors are all single-phase. For the Ba9Y1.52Si6O24:0.4Yb(3+),0.08Er(3+) sample, it has been found that the intensity ratio of the H-2(11/2)-I-4(15/2) to S-4(3/2)-I-4(15/2) emissions of Er3+ shows a continuous increase with increasing temperature upon 980 nm excitation owing to the well-known thermally coupled levels of Er3+. It was also found that decay lifetime on S-4(3/2) level of Er3+ changes with temperature. For the Ba9Y1.52Si6O24:0.4Yb(3+),0.08Ho(3+) phosphor, the green (F-5(4),S-5(2))-I-5(8) emission of Ho3+ exhibits a faster decay rate in intensity relative to the red F-5(5)-I-5(8) one when the measure temperature increases. The corresponding reason has been discussed by the energy level diagram and decay lifetime. For the Ba9Y1.58Si6O24:0.4Yb(3+),0.02Tm(3+) sample, it was found that the change of the emission intensity ratio of the Tm3+ 3H4-H-3(6) to (F-3(2),F-3(3))-H-3(6) transitions with the temperature follows the Boltzmann distribution. The sensitivities of the above phosphors were calculated, and the high sensitivity values indicate the present phosphors could be a promising candidate for optical temperature sensors. (C) 2017 Elsevier B.V. All rights reserved.