Structural, thermal, optical and dielectric studies on rare earth ion-doped borate glasses for solid state laser application

Light emission diodes (LEDs) are widely used in a variety of applications that are available today. With their tunability and long operation life-time, LEDs have surpassed the efficiency and functionality of conventional lighting systems like incandescent and luminescence light sources. Commercial LEDs are typically fabricated using a blue chip coated with yellow phosphor. However, this fabrication method lacks of a red-light component which induces poor thermal stability. A solution to this is to replace phosphors with glass. This work aims to fabricate glass hosts doped with rare earth (RE) elements for better thermal stability and lower power consumption. Firstly, the singly Dy3+-doped borate glasses with nominal composition (60-x) B2O3- 10 ZnO-10 PbO-10 Na2O-10 CaO-(x) Dy2O3 (x = 0, 0.1, 0.2, 0.5, 0.75, 1.0, 1.5 and 2.0 mol%) were prepared by using the melt quenching technique which were characterized using X-ray Diffraction (XRD) and Scanning electron microscope (SEM) to confirm the amorphous nature of the glasses and energy dispersive x-ray analysis (EDAX) to validate that all related elements were present in the synthesized glasses. The thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements were also performed to study thermal properties, where ΔT >100 °C (ΔT=Tx – Tg) for all the glasses. Among all tested Dy3+-doped glasses, 0.75 mol% Dy3+-doped glass showed the highest photoluminescence (PL) intensity with four emissions, where the two transitions corresponded to 4F9/2→ 6H15/2 (blue) and 4F9/2→ 6H13/2 (yellow) were observed to be more intensified than the others. The Commission International de l'Eclairage (CIE) chromaticity (x,y) coordinates for BZPNCDy 0.1 mol% glass are (0.398, 0.430), close to the white light region in the CIE 1931 chromaticity diagram. The work was continued with fabricating singly doped Tb3+ and Sm3+ ions along with co-doped Tb3+/Sm3+ borate glasses via melt quenching technique. Both TGA and DSC analysis were conducted to explore the material’s thermal properties. Among all Tb3+/ Sm3+ co-doped glasses, the (Tb0.5-Sm0.5) glass shows the highest emission intensity with respect to others. A total of five emission bands were found, where two were from Tb3+ transitions corresponding to 488 nm (blue) (5D4 → 7F6) and 543 nm (green) (5D4 → 7F5). Three emission bands for Sm3+ at 563 nm (green), 599 nm (orange-red) and 645 nm (red) according to 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, and 4G5/2 → 6H9/2 electronic transitions have been identified. The calculated CIE chromaticity (x,y) coordinates for singly doped Tb3+ (Tb0.5) green emission, singly doped Sm3+ (Sm0.5) orange-red emission, and co-doped Tb3+/ Sm3+ (Tb0.5-Sm0.5) yellow emission are (0.343, 0.584), (0.607, 0.389), and (0.438, 0.515), respectively, following the CIE 1931 chromaticity diagram.

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