Emission features of Er³⁺ ions in an exotic SeO₂ based glass system

In this work we have studied impact of SeO₂ concentration on luminescence properties of 39PbO-(60-x)B₂O₃-xSeO₂:1.0 Er₂O₃ ( 10 ≤ x ≤ 50) glass system. The structural analysis of the samples carried out by XRD, SEM indicated that the prepared samples are in amorphous phase. IR, Raman and XPS studies revealed increasing presence of isolated selenite [SeO₃]²⁻groups and decreasing concentration of [SeO₄]²⁻(selenate) groups with increasing content of SeO₂ in the glass network. Optical absorption (OA) spectra revealed absorption bands due to ⁴I_15/2 → ⁴F_7/2, _9/2, ²H_11/2, ⁴S_3/2, ⁴I_9/2, _11/2, _13/2 transitions of Er³⁺ ions. Using J-O theory, the spectra were characterized and the evaluated Ω_λ parameters are found to be in the order: Ω₂ > Ω₄ > Ω₆. The PL spectra recorded at λ_exc= 378 nm exhibited the emission bands due to ²H_11/2→⁴I_15/2 (B), S_3/2→⁴I_15/2(G), ⁴F_9/2→⁴I_15/2(O) and ⁴I_13/2→⁴I_15/2 (NIR) transitionsof Er³⁺ ions. With the gradual increase SeO₂ content, the PL emission bands (especially green and NIR bands) have exhibited significant growth. The spectra were quantitatively analysed using kinetic rate equations and the causes for enhancement of PL emission were recognised and discussed. From the gain co-efficient G(λ) of the ⁴I_13/2→⁴I_15/2 transition, its lasing behaviour is detected for a population inversion of nearly 50%.