Thermodynamics and up-conversion of Cr3+/Ho3+ Co-doped 12CaO·7Al2O3 synthesized in argon

Abstract

A thorough study for thermodynamics characters and optical properties of pure 12CaO·7Al2O3 (C12A7) prepared under “argon” (Ar) and Cr3+/Ho3+ co-doped C12A7 (C12A7-Cr3+/Ho3+) derivatives have been made by using XRD, DSC/TG, Raman spectra and fluorescence spectrophotometer analysis, respectively. The precursor powders were calcined from 298 K to 1473 K under Ar atmosphere for studying their thermodynamics behaviors after co-precipitation. The relative chemical reactions for C12A7 were confirmed and determined by XRD, DSC/TG, Raman, FTIR and EDX analysis. Activation energies of crystal growth and extraction of free “O2−” for C12A7 polycrystals sintered under Ar atmosphere were measured to be (687/666) and (230/208) kJ/mol according to Ozawa/Kissinger methods, respectively. Crystallization parameters of pure C12A7 polycrystals in “Ar” gas were evaluated to be m = 3 and n = 3 with a 3D growth mechanism of constant nuclei. Visible up-conversion emissions at 470 nm and 540 nm were observed from C12A7-Cr3+/Ho3+ powders under 808 nm Xe lamp excitation. We proposed four relaxations and cooperative transformation mechanisms of Cr3+/Ho3+ to explain those up-conversion processes, which are one for 470 nm and three for 540 nm light respectively.