Compositional dependence of white light emission in Dy3+ doped NaCl - BaO bismuth borate glasses

The present study deals with synthesis, characterization and analysis of dysprosium doped NaCl - BaO-Bi2O3-B2O3 glass samples so as to evaluate its feasibility in solid state lighting applications. Various analytical investigations viz. X-ray diffraction (XRD), density, molar volume measurement, Fourier Transfer Infrared (FTIR) Spectroscopy, UV-Vis-NIR and photoluminescence (PL) has been carried out to study the impact of replacing BaO by NaCl content on white light emission parameters in the host glass matrix. The glassy nature of the prepared samples was confirmed through peak free X-ray diffraction profiles. FTIR spectroscopy reveals the network modifier role of NaCl as four coordinated boron are converted into three coordinated ones. Six absorption peaks from H-6(15/2) ground state to I-4(15/2), F-6(5/2), F-6(7/2), F-6(9/2), H-6(9/2), H-6(11/2) excited states were observed from UV-Vis-NIR spectra of all glass samples. The fundamental absorption edge, optical band gap and Urbach energy were calculated and reported in the present study. Excitation spectra recorded at 578 nm provide six excitation peaks at 349, 363, 386, 425, 452, 471 nm. The highly intense peak at 452 nm was further selected to record the emission spectra and four prominent peaks centred at 484 nm (blue), 578 nm (yellow), 668 nm (red) and 755 nm due to various F-4(9/2),H-6(J)(J = 9/2, 11/2, 13/2, 15/2) radiative transitions in visible and near infrared region of the spectra were observed. From emission spectra various parameters viz. Y/B ratio, (x,y) chromaticity coordinates, and correlated color temperature (CCT) were determined. The Y/B ratio for all the glass samples was found to be greater than 1 signifying a covalent bonding between Dy3+ and O2- ions. The obtained (x,y) coordinates shows a balanced white emission (0.36, 0.39) which is quite stable with varying compositions. The value of CCT for present glass system was found to lie between 4339-4537 K which is a characteristic of near the white light region marking the suitability of synthesized glasses as an alternative materials for solid state lightening applications.