Optical transitions and frequency upconversion of Er^3+ ions in Na_2OCa_3Al_2Ge_3O_12 glasses

Er3+-doped and Er3+/Yb3+-codoped Na2O·Ca3Al2Ge3O12 glasses that are suitable for use in optical waveguide devices have been fabricated and characterized. The density, the refractive indices, the optical absorption, the Judd–Ofelt parameters, and the spontaneous transition probabilities of the glasses have been measured and calculated. Intense 1.533-µm fluorescence was observed in these glass systems under 798- and 973-nm excitation, and the quantum efficiency was ∼100%. Efficient upconversion luminescence at 525, 547, and 659 nm at room temperature was also observed. At a pump intensity of 1220 W/cm2 at 798 nm, frequency upconversion efficiencies of 0.98×10-2 and 1.03×10-2 were obtained for green and red emissions, respectively. The standardized value for green emission is higher than those reported for lead germanate, lead tellurium germanate, silicate, and phosphate glasses. Under 973-nm excitation, the enhancement of 1533-nm emission and visible upconversion fluorescence in Er3+/Yb3+-codoped glasses are confirmed, and the sensitizing is due to efficient energy transfer from Yb3+ to Er3+.