1.47-μm emission and multiphonon relaxation of Tm³⁺ ions in potassium bismuth gallate glasses

We propose and demonstrate potassium bismuth gallate (KBG) glasses as suitable hosts for the rare-earth ion Tm³⁺ (thulium) operating at the 1.47-μm wavelength. The optical properties of Tm³⁺-doped KBG glasses were investigated. The bandwidth of the ³⁺H₄ → ³⁺F₄ transition is -120 nm and is higher than that of Tm³⁺-doped, tellurite-based glasses. The measured fluorescence lifetime is 0.15 ms at room temperature, and the quantum efficiency is 88%. Multiphonon relaxation rates for various transitions were evaluated and compared with other glass hosts. The energy transfer in Tm³⁺-Ho ³⁺-codoped KBG glasses was also investigated, and these results indicate that Tm³⁺-doped KBG glasses are promising candidates for efficient broadband optical amplifiers operating in the 1.47-μm wavelength range.