Judd-Ofelt analysis, frequency upconversion, and infrared photoluminescence of Ho³⁺ -doped and Ho³⁺/ Yb³⁺ -codoped lead bismuth gallate oxide glasses

Ho³⁺ -doped and Ho³⁺/ Yb³⁺ -codoped lead bismuth gallate (PBG) oxide glasses were prepared and their spectroscopic properties were investigated. The derived Judd-Ofelt intensity parameters ( ₂ =6.81× 10^-20 cm², ω₄ =2.31× 10^-20 cm², and ω₆ =0.67× 10^-20 cm²) indicate a higher asymmetry and stronger covalent environment for Ho³⁺ sites in PBG glass compared with those in tellurite, fluoride (ZBLAN), and some other lead-contained glasses. Intense frequency upconversion emissions peaking at 547, 662, and 756 nm as well as infrared emissions at 1.20 and 2.05 μm in Ho³⁺ / Yb³⁺ -codoped PBG glass were observed, confirming that energy transfer between Yb³⁺ and Ho³⁺ takes place, and a two-phonon-assisted energy transfer from Yb3+ to Ho3+ ions was determined by the calculation using phonon sideband theory. The 1.20 μm emission observed was primarily due to the weak multiphonon deexcitation originated from the small phonon energy of PBG glass (∼535 cm-1). A large product of emission cross-section and measured lifetime (9.93× 10^-25 cm² s) was obtained for the 1.20 μm emission and the gain coefficient dependence on wavelength with population inversion rate (P) was performed. The peak emission cross-section for 2.05 μm emission was calculated to be 4.75× 10^-21 cm². The relative mechanism of Ho³⁺ -doped and Ho³⁺ / Yb³⁺ -codoped PBG glasses on their spectroscopic properties was also discussed. Our results suggest that Ho ³⁺ / Yb³⁺ -doped PBG glasses are a good potential candidate for the frequency upconversion devices and infrared amplifiers/lasers.