Crystallization and luminescence properties of Er/Yb-doped glass-ceramics based on A₂O-ZnO-SiO₂ system (A = Li, Na, K, Cs)

Er/Yb-doped glass-ceramics from the A2O-ZnO-SiO2 system (A = Li, Na, K, Cs) were prepared. The glass-ceramics contained different crystalline phases, including zinc oxide ZnO, zinc silicate Zn2SiO4 (willemite) or alkali zinc silicates A2ZnSiO4. The tendency to crystallize was shown to increase with decreasing radius of the alkali ions, from Cs+ to Li+. The Na2O-ZnO-SiO2 system was found to be favorable for the crystallization of the rhombohedral modification of Zn2SiO4 (willemite) while the K2O-ZnO-SiO2 system was shown to contain the largest amount of ZnO (zincite). The high crystallinity of the samples caused by annealing the samples to temperatures above 800 degrees C resulted in a significant increase in the emission intensity around 1.5 mu m, a change in the shape of the luminescence band and an increase in the emission lifetime at 1.5 mu m from a value cca 10 ms up to a 15 ms.