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• SeO 2 based glasses of composition 39PbO-(60- x)B 2 O 3 - x SeO 2 :1.0 Er 2 O 3 were synthesized. • IR/Raman spectra suggested growth of [SeO 3 ]2−/[SeO 4 ]2− units' ratio with SeO 2 content. • Analysis of OA spectra indicated J-O parameters to follow the order: Ω 2 > Ω 6 > Ω 4. • Green and NIR PL emission bands exhibited significant growth with SeO 2 content. • PL spectra quantitatively analysed using kinetic rate equations. • Gain co-efficient G(λ) of 4I 13/2 →4I 15/2 transition indicated its lasing behaviour. In this work we have studied impact of SeO 2 concentration on luminescence properties of 39PbO-(60- x)B 2 O 3 - x SeO 2 :1.0 Er 2 O 3 (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 [SeO 3 ]2−groups and decreasing concentration of [SeO 4 ]2−(selenate) groups with increasing content of SeO 2 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: Ω 2 > Ω 4 > Ω 6. 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 SeO 2 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%. [ABSTRACT FROM AUTHOR]