Judd-Ofelt analysis, visible to NIR photoluminescence emission under 450 nm and 976 nm excitations and energy transfer of barium fluorotellurite glasses doping with Ho3+, Yb3+, Ho3+:Yb3+

Barium fluorotellurite glasses doping with Ho³⁺, Yb³⁺, and Ho³⁺:Yb³ were fabricated using the conventional melt and quenching method, and their optical properties were studied using different optical spectroscopic techniques. The FITR absorption band at 3000 cm^-1 was used to investigate OH- concentrations of the prepared glasses, which increased with Yb³⁺ content. However, it decreased by substituting a portion of BaF₂ content with Ba₂CO₃ concentration. The electric dipole line strengths and Judd-Ofelt parameters were estimated using UV-visible-near infrared (NIR) optical absorption spectra to gain information on the rare earth ions doped glasses for laser applications. The various radiative parameters such as line strengths, optical intensity, and radiative rates from the higher energy levels, including ⁵F₄ + ⁵S₂, ⁵F₅, ⁵I₄, ⁵I₅, ⁵I₆ and ⁵I₇, to the ground state, ⁵I₈ have been reported and discussed. The influence of the Yb³⁺ and Ba₂CO₃ concentrations on the upconversion and downconversion photoluminescence emission intensities of the glasses prepared have been investigated by pumping with 450 nm and 976 nm excitation sources.  Under 450 nm and 976 nm, the NIR photoluminescence emissions reveal a band ranging from 980 nm to 1220 nm attributing to an overlap between Yb³⁺ and Ho³⁺ transitions. The influence of Yb³⁺ concentration on photoluminescence lifetime at the ²F_5/2 → ²F_7/2, ⁵F₄ + ⁵S₂  →⁵I₈  and  ⁵I₆  →⁵I₈  transitions under 976 nm laser excitation has been studied and reported. The results indicate that lifetime decreases with increasing Yb³⁺ concentration attributing to an efficient energy transfer from Yb³⁺ to Ho³⁺ ions. The energy transfer efficiency from Yb³⁺ → Ho³⁺ has been examined, which rises from 30% to 47% upon increasing Yb³⁺ content. Nevertheless, it decreases with the mixing of BaF₂ and Ba₂CO₃ lattice modifier contents. The results demonstrated that the 1200 nm (⁵I₆  →⁵I₈   transition) has remarkable potential for developing fiber lasers.