Structure refinement and up-conversion of Ho3+/Er3+ Co-doped 12CaO•7Al2O3

Crystal structures, thermodynamics characters and optical properties of pure 12CaO center dot 7Al(2)O(3) (C12A7) and Ho3+/Er3+ co-doped C12A7 (C12A7-Ho3+/Er3+) derivatives have been studied using XRD, DSC/TG and Raman spectra analysis, respectively. Testing samples were sintered at 1173 K from compacted precursor powders after co-precipitation. Effect of pH change on grain size of C12A7 was estimated via Scherrer's Equation. Activation energy of crystal growth for C12A7 polycrystals was measured according to Kissinger/Ozawa methods to be 238/258 kJ.mol(-1) respectively. Lattice constant (a) and Reference Intensity Ratio (RIR) of pure C12A7 were evaluated to be a = 12.0122(2) angstrom and RIR = 0.79 (5%). Fluorescence effects of Raman spectra around 1200-1400 and 2000-2500 cm(-1) and pure visible up-conversion emission of 520-540 nm were observed from C12A7-Ho3+/Er3+ powders under 488 nm laser diode and 793 nm Xe lamp excitation, respectively. Three relaxations and cooperative transformation mechanisms of Ho3+/Er3+ ions were proposed to explain up-conversion of pure green light process. (C) 2016 Elsevier Ltd. All rights reserved.