Spectroscopic study of Er³⁺ doped borate glass system for green emission device, NIR laser, and optical amplifier applications

The 10BaO–20ZnO–20LiF-(50-x)B₂O₃-xEr₂O₃ (x = 0, 0.1, 0.5, 0.7, and 1.0 mol %) glass system was studied for green emission device, NIR laser, and optical amplifier applications. The impact of Er³⁺ doping was assessed through structural, optical, and thermal properties. The Er³⁺ ions behaved as network modifiers and decreased the network rigidity by the transformation of [BO₄]→[BO₃] and Non-Bridging Oxygens. This was consistent with the decrease in the glass transition temperature. Ten absorption peaks of Er³⁺ ion equivalent to transitions from ⁴I_15/2 to various excited levels were quantified through their oscillator strengths. Through broadband impedance spectroscopy, the insulating property of the glass system was authenticated by the persistence of dc-conductivity in the order of 10⁻¹⁰ Scm⁻¹ up to 523 K. With 378 nm excitation, a violet emission (²H_9/2→⁴I_15/2) and two intense green emissions (²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2) were noticed. The NIR emission (⁴I_13/2→⁴I_15/2) was observed at 1531 nm with 378 and 980 nm excitations and the corresponding decay curves were recorded. The Inokuti-Hirayama model indicated the increase in the energy transfer and reduction in critical distance amid the Er³⁺ ions with doping leading to energy migration through cross-relaxations and lifetime quenching. The laser parameters were determined from Fuchtbauer-Ladenburg theory. The color coordinates of the samples were lying in the green region, with purity >89% and CCT >6000 K. The gain coefficient from McCumber theory was positive for a population inversion >50%, with a wide gain between 1460 and 1565 nm, extending the application of the glass system as an optical amplifier in the S + C communication window.