Luminescence properties and energy transfer from Gd³⁺to Tb³⁺ions in gadolinium calcium silicoborate glasses for green laser application

The Tb³⁺-doped gadolinium calcium silicoborate (BSGdCaTb) glasses of composition (55-x) B₂O₃- 10 SiO₂- 25 Gd₂O₃-10 CaO -x Tb₂O₃, where x = 0.01, 0.05, 0.1, 0.5, 1.0, and 2.0 mol %, have been prepared by conventional melt quenching technique and are characterized through thermal, absorption, excitation, emission and decay rate measurements. The optical band gap (E_opt) and Urbach's energies (ΔE) have been evaluated taking into account the ultraviolet (UV) edge of absorption spectra. The Tb³⁺-doped BSGdCaTb glasses exhibit strong emission in the green (⁵D₄ → ⁷F_J, J = 3,4,5 and 6) and very weak emission in the ultraviolet blue (⁵D₃ → ⁷F_J, J = 3,4,5 and 6) transitions under excitation at 275 nm, respectively. The intensity of the⁵D₄ → ⁷F₅(green at 543 nm) and⁵D₃ → ⁷F₄(blue at 436 nm) emissions and their integrated intensity ratios (I_G/I_B) and (I_B/I_G) under 275 nm excitation have been obtained as a functions of Tb³⁺concentration, respectively. The emission intensity of Gd³⁺at 312 nm decreases with increasing of Tb₂O₃concentration, while emission intensity of Tb³⁺increases upto 1.0 mol % concentration of Tb₂O₃. The Tb³⁺ion decay time for⁵D₄level has been determined and is found to be slightly decreases with increasing of Tb₂O₃concentration. The CIE color coordinates and color purity have been calculated for Tb³⁺-doped glasses and it have found to be shift towards the bright green region with increasing of Tb³⁺ion concentration in BSGdCaTb glasses.