Thermal analysis and optical properties of Yb^3+/Er^3+-codoped oxyfluoride germanate glasses

Abstract

Yb3+/Er3+-codoped Na2O–Al2O3–GeO2–PbO–PbF2 glasses that are suitable for use in fiber lasers, amplifiers, and waveguide devices have been fabricated and characterized. The density, refractive indices, optical absorptions, Judd–Ofelt parameters, and spontaneous-transition probabilities of the glasses have been measured and calculated. Intense and broad 1.53-μm infrared fluorescence and visible upconversion luminescence were observed under 976-nm diode laser excitation. For the 1.53-μm emission band, the full widths at the half-maximum increase and the peak wavelengths are blueshifted with an increase of PbF2. The stimulated-emission cross sections were calculated from the measured-absorption cross section according to the McCumber theory. The monotonically reduced emission cross section arises from the decreased refractive indices of glasses and the increased linewidth of the infrared fluorescence spectrum. For the upconversion emissions centered at 524, 547, and 660 nm, the emission intensity changes remarkably with PbF2 contents from 0 to 15 mol.%. The quadratic dependence of the green and red emissions on excitation power indicates that a two-photon absorption process occurs under the 976-nm excitation. The relatively long lifetimes of the Er3+ 4S3/2 and 4F9/2 levels for the NAGF3 glass gives rise to a much more intense upconversion emission.