Optical transitions and frequency upconversion of Er³⁺ ions in Na₂O · Ca₃Al₂Ge₃O₁₂ glasses

Er³⁺-doped and Er³⁺/Yb³⁺-codoped Na ₂O · 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 × 10²s and 1.03 × 10² 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⁺. © 2001 Optical Society of America.