Up/Downconversion properties in oxyfluoride glass ceramics containing Er³⁺-doped CaF₂

Abstract

Oxyfluoride glass ceramics containing Er³⁺-doped CaF₂ nanocrystals were prepared by heat-treatment of as-made glasses at various temperatures. Coordination environment of Er³⁺ ions was evaluated by the Judd-Ofelt analysis. Omega 2 parameter, which represents the magnitude of asymmetry of the Er³⁺ site, decreased with increasing heat-treatment temperature. The Er³⁺ ions moved from the oxide glass matrix to the fluorite crystals with low phonon energy after the ceramization. Therefore, the intense upconversion luminescence due to ⁴S_3/2->⁴I_15/2(550nm) and ⁴F_9/2->⁴I_15/2(660nm) were observed. In addition, the cross relaxation (⁴F_5/2->⁴F_9/2):(⁴I_15/2->⁴I_13/2) was promoted by shortening of the interionic distance of Er³⁺ ions in the CaF₂ crystals. We also found a quantum cutting process attributed to ⁴S_3/2->⁴I_13/2->⁴I_15/2.