Blue–green luminescence properties and energy transfer in Tm³⁺/Tb³⁺ co-doped TeO₂–GeO₂–Bi₂O₃–BaF₂ glass

Tm³⁺/Tb³⁺ co-doped TeO₂–GeO₂–Bi₂O₃–BaF₂ glasses were synthesized via high-temperature melt-quenching to achieve blue–green fluorescence emission. Under 808-nm pump excitation, the TGBB2 sample (Tm₂O₃:Tb₄O₇ = 3:8) exhibited balanced emissions at 452 nm (blue, Tm³⁺: ¹G₄ → ³H₆) and 544 nm (green, Tb³⁺: ⁵D₄ → ⁷F₅). With increasing Tb³⁺ concentration, green emission intensity increased while blue emission decreased, confirming efficient Tm³⁺ → Tb³⁺ energy transfer. Key performance metrics for TGBB2 included: a forward energy transfer coefficient of 571.83 × 10⁻⁴⁰ cm⁶/s (far exceeding the reverse coefficient of 63.12 × 10⁻⁴⁰ cm⁶/s), an energy transfer efficiency of 99.5%, maximum emission cross-sections of 5.87 × 10⁻²¹ cm² (476 nm, Tm³⁺) and 3.37 × 10⁻²¹ cm² (486 nm, Tb³⁺), and corresponding gain coefficients of 2.98 cm⁻¹ and 0.46 cm⁻¹. These results validate the glass’s low laser threshold, making Tm³⁺/Tb³⁺ co-doped tellurite–germanate–bismuthate glass a promising candidate for blue–green laser communication and underwater optical transmission.