Optical transitions in Er³⁺ doped lead germanate glasses

Er^3+- and Er^3+/Yb^3+-doped lead germanate glasses that are suitable for use in fibre lasers and optical amplifiers as well as optical waveguide devices have been fabricated and characterized. The absorption spectra from near-infrared to visible were obtained and the Judd－Ofelt parameters were determined from the absorption band. Intense and broad 1.53μm infrared fluorescence and visible upconversion luminescence were observed under 976 nm diode laser excitation. For 1.53μm emission band, the full widths at half-maximum are 36, 37, 51 nm for GPE, GPYE and GPFE samples, respectively. For frequency upconversion emission, the intense bands centred at around 524, 545, 657nm are due to the ^4S_3/2+^2H_11/2→^4I_15/2 and ^4F_9/2→^4I_15/2 transitions of Er^3+ ions. The quadratic dependence of the green and red emissions on excitation power indicates that the two-photon absorption process occurs under the 976nm excitation.