Optical properties of lead borate glasses containing Dy(3+) ions were examined using absorption and luminescence measurements and theoretical calculations based on the Judd-Ofelt framework and the Inokuti-Hirayama model. The luminescence spectra show two characteristic bands at 480 and 573 nm, which are due to (4)F(9/2)-(6)H(15/2) (blue) and (4)F(9/2)-(6)H(13/2) (yellow) transitions of trivalent Dy(3+) ions. The yellow/blue luminescence and its decay were analyzed as a function of activator concentration.

In this paper, a 2 µm broadband emission under 796 nm laser diode excitation in low phonon energy GeO₂-Ga₂O₃-BaO glass system is co-doped with 0.7Tm₂O₃/(0.07-0.7)Ho₂O₃ (mol%). The widest emission band (where the Tm³⁺ → Ho³⁺ energy transfer efficiency is 63%) was obtained for 0.7Tm₂O₃/0.15Ho₂O₃ co-doped glass from which a double-clad optical fiber was realized and investigated. Optimization of Tm³⁺/Ho³⁺ concentration enabled the acquisition of broadband amplified spontaneous emission (ASE) in double-clad optical fiber with a full width at half maximum (FWHM): 377 nm and 662 nm for 3 dB and 10 dB bandwidth, respectively. ASE spectrum is a result of the superposition of (Tm³⁺: ³H₄ →Η³F₄) 1.45 µm, (Tm³⁺: ³F₄ → ³H₆) 1.8 µm and (Ho³⁺:⁵I₇ → ⁵I₈) 2 µm emission bands. Hence, highly rare-earth co-doped germanate glass is characterized by a remarkably broader ASE spectrum than silica and tellurite fibers showed promising lasing properties for their further application in tunable and dual wavelength lasers.