Temperature-sensing luminescent materials La9.67Si6O26.5:Yb3+-Er3+/Ho3+ based on pump-power-dependent upconversion luminescence
Rare earth ions doped upconversion (UC) luminescent materials could show potential applications in optical temperature sensing. To develop new UC phosphors doped with Yb3+/Ho3+ activators, a series of La9.67Si6O26.5:Yb3+-Er3+/Ho3+ samples were prepared by solid-state reaction method, and the temperature-sensing properties were evaluated on the basis of the UC spectra. The phase, structure and morphology of the samples were analyzed by XRD, Rietveld refinement and SEM techniques, respectively. The characteristic emission peaks of both Er3+ and Ho3+ appeared and the corresponding UC mechanism was discussed. Different strategies of optical temperature sensing were employed for Er3+ and Ho3+. The fluorescence intensity ratio (FIR) for the two green emissions of Er3+ originating from thermally-coupled levels follow the Boltzmann distribution. The effect of pump power on the sensor sensitivities was investigated in detail. The relative standard deviation and temperature uncertainty were also evaluated. For Ho3+-activated LSO, the red and green emissions derived from non-thermally-coupled levels were used for temperature sensing. The detailed UC energy transfer processes were discussed to explain the change of the FIR with temperature. High absolute sensitivity was obtained in this phosphor. The above investigations could be instructive in exploring other new luminescent materials for optical temperature sensing.