Highly sensitive optical temperature sensing based on pump-power-dependent upconversion luminescence in LiZnPO(4):Yb(3+)–Er(3+)/Ho(3+) phosphors

In this work, various LiZnPO(4):0.5 mol% Ln(3+) (Ln = Ho, Er) phosphors with different Yb(3+) ion doping concentrations were synthesized by a sol–gel/Pechini method. X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques were used to evaluate the phase and morphology of the samples. The UC process was mentioned as the typical emission peaks of Er(3+) and Ho(3+). For Er(3+) and Ho(3+), different optical temperature sensing methods are included. The Boltzmann distribution was accompanied by the fluorescence intensity ratio (FIR) for the two green Er(3+) emissions originating from thermally-coupled levels. The effect of pump power on sensor sensitivities was extensively studied. The temperature uncertainty is also evaluated. The red and green emissions generated from non-thermally-coupled levels were used for temperature sensing in the Ho(3+)-activated LiZnPO(4). High sensitivities were obtained in the phosphors, and the LiZnPO(4):Yb(3+)/Ho(3+) showed the largest absolute sensitivities. LiZnPO(4):Yb(3+)–Er(3+)/Ho(3+) phosphors may be useful in the development of new luminescent materials for optical temperature sensing.