Synthesis and enhanced upconversion luminescence upon two-wavelength excitation of Er3+:CaF2 transparent ceramics

High optical quality of Er³⁺:CaF₂ transparent ceramics were successfully fabricated by hot pressing method. The maximum transmittance reached to 93% which was close to theoretical transmittance in 2 mol% Er³⁺:CaF₂ transparent ceramics. The upconversion luminescence of ceramics samples were investigated in detail upon 980nm, 808nm excitation and 980nm+808nm two-wavelength excitation, respectively. UC transition mechanism about red emission at 808nm excitation was different from that at 980nm excitation. Owing to the synergistic effect at simultaneous 980nm and 808nm excitation, energy losses caused by multi-phonon relaxation and the energy mismatch between 4f levels and excited photons could be suppressed. The strategy of multi-wavelength excitation might broaden the applications of upcoversion ceramics materials.