Thermochromic Pr3+ doped CaMoO4 phosphor with diverse thermal responses for temperature sensing

Abstract

CaMoO4:Pr3+ thermochromic phosphors with diverse thermal responses for temperature sensing were prepared by the traditional solid-phase reaction method. The typical CaMoO4:Pr3+ had scheelite structure belonging to tetragonal crystal system and space group of I41/a (88). Pr3+ ions can be easily substituted for Ca2+ ions of host CaMoO4 because of similar ionic radius. CaMoO4: 1.5% Pr3+ have the block structure with mean size of 6.84 μm. The Eg (∼3.93 eV) value of pure CaMoO4 is bigger than that (∼3.65 eV) of CaMoO4: 1.5%Pr3+, attributing to the existence of intermediate defect energy levels. Appropriate Pr3+ doping concentration is 1.5%, and the concentration quenching phenomenon can be explained by the concrete electric multipole type of d-d interaction. The emission peak at ∼605 nm from 1D2→3H4 transition have a good thermal stability of 99.452%@423 K, while the wide band centered at ∼490 nm from 3T1,2 → 1A1 transition in the MoO42− complex and 3P0→3H4 transition in Pr3+ have a poor thermal stability of 27.572%@423 K. Calculated activation energy is 0.239 eV. Temperature-dependent FIR for optical thermometry was constructed due to their diverse thermal responses. CaMoO4: Pr3+ phosphor had good relative sensitivities of 2.216%, 0.969% and 0.932% based on FIR of I605 nm/I490 nm with Boltzmann distribution, modified Boltzmann distribution and exponential equation fitting. Thermochromic behavior and thermal quenching mechanism are investigated. The obtained relative sensitivity is better than that of most phosphors, implying that CaMoO4: Pr3+ has a potential for application in optical thermometry.