Structure and upconversion luminescence of transparent glass-ceramics containing (Er,Yb)2(Ti,Zr)2O7 nanocrystals

Transparent spinel-based glass-ceramics are synthesized on the basis of the magnesium aluminosilicate glass with the addition of nucleating agents (a mixture of TiO 2 and ZrO 2 ) and dopants, Er 2 O 3 and Yb 2 O 3 , by a secondary heat-treatment at 800–1050 °C. The precipitation of rare-earth titanate–zirconate (Er,Yb) 2 (Ti,Zr) 2 O 7 nanosized (5–17 nm) crystals is observed, as well as their transformation from the defect-fluorite to the disordered pyrochlore structure. Optical absorption and upconversion luminescence spectra are studied for various Er/Yb ratios, as well as for single Er-doped glasses and glass-ceramics. A substantial enhancement (10-times) of the red emission (~ 650 nm) with the heat-treatment is observed and explained with the analysis of the results of lifetime measurements of the 2 H 11/2 , the 4 S 3/2 , the 4 F 9/2 and the 4 I 11/2 excited states of Er 3 + ions. The mechanisms of upconversion in (Er,Yb) 2 (Ti,Zr) 2 O 7 nanocrystals are discussed.