Influence of Different Alkali Fluorides (LiF/NaF/KF) on Photoluminescence Properties of Dy3+ and Eu3+ Rare Earth Ion Co-Doped Borate Glasses

In this work, dysprosium (Dy3+) and europium (Eu3+) rare earth (RE) ion co-doped bismuth borate glasses with different alkali fluorides (Li+, Na+, and K+) and Al3+ ions were prepared by the melt quenching technique. Various techniques were carried out to investigate the impact of alkali fluorides on the luminescence properties of the prepared mixed rare earth ion (Dy3+ and Eu3+) glasses. The glassy nature was confirmed by the presence of humps in x-ray diffraction patterns. Density and molar volume were calculated via Archimedes principle to examine physical properties, which shows a decreasing trend from 5.30 to 3.34 in density with the addition of alkali fluorides. Fourier transform infrared spectroscopy was used to study the structural properties, and revealed the presence of traditional bismuth and borate groups along with metallic and cationic vibrations of alkali and RE ions. Ultraviolet-visible and near-infrared absorption spectroscopy was performed to investigate the optical properties. The indirect optical bandgap was estimated and displayed an increasing trend from 2.88 to 3.34 eV, which confirmed the suitability of this material for use in optoelectronic devices. With alkali fluorides, the Urbach energy was decreased from 0.25 to 0.14 eV, which indicated a smaller number of defects. To assess the luminescent behaviour, photoluminescence spectroscopy was executed to record both excitation and emission spectra of glasses for a variety of excitation wavelengths. Under varying excitations, the synthesized glasses showed three distinct emissions in the blue, yellow, and red regions. The primary sources of the blue and yellow emission were the Dy3+ ion transitions F-4(9/2) -> H-6(15/2) and H-6(13/2), whereas the red emission was produced by the Eu3+ ion transition D-5(0) -> F-7(2). Colorimetric analysis was carried out on the emission spectra, and colour parameters were obtained. The CIE (Commission Internationale de l'Eclairage) colour coordinates of composition DEABB were identified as (0.32, 0.32), which lie closest to white light coordinates (0.33, 0.33). This confirmed that the prepared samples demonstrated excellent emission properties and could be proposed for use as white light and orange-red light sources in solid-state lighting applications.