Influence of Dy3+ions on the physical, thermal, structural and optical properties of lithium zinc phosphate glasses

https://doi.org/10.1016/j.jnoncrysol.2020.120622Get rights and content

Highlights

  • Dy3+ ions doped lithium zinc phosphate glasses are prepared.

  • Thermal characterization, optical and structural studies has been done.

  • Luminescence quenching is observed at 1 mol% Dy2O3.

  • Y/B >1, indicating low symmetry and high degree of covalence between Dy3+&O2−.

  • CIE coordinates are close to standard white light illumination point (0.33, 0.33).

Abstract

Lithium zinc phosphate glasses activated with dysprosium ions were prepared by following the melt quenching method. The X-ray diffraction patterns confirmed the non-crystalline structure of the prepared glasses. All the physical parameters are calculated using appropriate formulae. Glass transition (Tg), melting (Tm) and crystallization (Tc) temperature were determined by analyzing the differential thermal curves and these values were used to determine certain thermal parameters. The thermal stability parameter was found to be greater than 100˚C for all the glasses indicating good thermal stability of the glass samples. In order to examine the functional groups and study the structural properties of the prepared glasses, Fourier transform infrared spectrum was recorded for all the glasses. Refractive index is found to be increasing with increase in Dy2O3 concentration. Optical direct and indirect band gaps were determined from Tauc's plots. The emission spectra showed two intense bands at 483 nm (blue) and 574 nm (yellow) along with two feeble bands at 663 nm and 752 nm which are the essential requirements for white LED applications. The maximum luminescence intensity was found in the glass sample with 1mol% Dy2O3. Yellow/Blue intensity ratio, chromaticity coordinates and the correlated color temperature are calculated for all the glass samples. The color coordinates obtained are found to be in the white light region of the CIE 1931 diagram indicating the possibility of using these glasses for white light generation.

Introduction

Trivalent lanthanide ions doped glasses are being widely studied from a very long time as they are excellent photo-luminescent materials [1], [2], [3], [4]. The white LEDs which are commercially available are generally prepared by coating the yellow phosphors on the surface of blue LED chips. The white light from these LED's has weak emission and short life-time, which is the result of uneven coating of phosphors on the chips [5], [6], [7]. Therefore, plenty of research is going on so as to develop rare-earth ions doped glasses and also crystals to overcome the above-said problem. Also, the rare-earth ions doped glasses usually have excellent luminescence, high thermal stability and most importantly, the production cost is low as compared to phosphor-coated LEDs [8], [9], [10]. These glasses emit different wavelengths depending on the RE3+ concentrations and the neighbouring circumstances. From various studies, it is well known that dysprosium is an excellent optical activator and offers simultaneous red, yellow and blue emissions suitable for optical amplification and laser action. Also, the prominent emission bands at blue (483 nm) and yellow (574 nm) region make dysprosium ion a promising element for white light applications [11], [12], [13]. Thus, Dy3+activated lithium-zinc-phosphate glasses have been prepared and studied to see the possibility of using these glasses as luminescent materials as well as optical fibres. Among the various oxide glasses which are well known such as, silicate, tellurite, phosphate and borate,phosphate glasses have exclusive characteristics like more transparency, low melting point, significant solubility of RE ions, fewer dispersions, low refractive index and also possess a flexible network structure which admits a number of changes to mend or enhance specific properties [14], [15], [16], [17]. ZnO is a well-known network former as well as a network modifier and Li2O is a network modifier [18], [19], [20]. These two are included in the glass matrix to help in reducing the hygroscopic nature of phosphate and increase the chemical resistance of the glasses.

Vijaykumar et al. [21] studied and reported the Dy3+ doped aluminofluro borophosphate glasses exciting at 386 nm suitable for WLED and laser applications. Nagaraja Naick et al. [11] has reported Dy3+doped different phosphate glasses for white light applications. Karki et al. [5] has studied the physical, optical and luminescence properties of barium borophosphate glasses varying Dy3+ concentration. Similarly, a number of studies on Dy3+doped glasses have been reported. However, reports on the detailed study of Dy3+ doped lithium zinc phosphate glasses are not found so far. In this paper, experimental and theoretical approach on the physical, thermal, structural and optical properties of Dy3+ doped lithium zinc phosphate glasses have been reported.

Section snippets

Experimental details

By melt quenching method, Dy3+ activated lithium zinc phosphate glasses with chemical composition, x Dy2O3 −40 P2O5 - (15-x) Li2O - 45ZnO (where x = 0, 0.1, 0.3, 0.5, 1.0, 1.5 and 2 mol%) were prepared. AR grade chemicals (from Sigma Aldrich, 99.99%) Dy2O3, LiOH.H2O, ZnO, and NH4H2PO4 were weighed (about 10 g per matrix) and using an agate mortar these chemicals were mixed well. These mixtures were then transferred to crucibles (porcelain) which were marked accordingly. These crucibles were

Results

X-ray diffraction patterns and SEM images confirmed the amorphous nature of the prepared glass samples. As the Dy2O3 concentration increases, more non-bridging oxygens are created which is leading to the increase in density, molar volume, refractive indices, electronic polarizability, optical basicity and decrease in the packing density, oxygen packing density and interaction parameter of the glasses. The internuclear distance (ri) and polaron radius (rp) are decreasing with increased Dy3+

X-ray diffraction and SEM-EDS analysis

Fig. 2 depicts the X-ray diffraction patterns obtained for the prepared Dy3+ doped glass samples. It is observed that there are no crystalline peaks except a broad hump between 20˚−30˚, clearly indicating the amorphous nature of the glass samples prepared.

The SEM images of all the glass samples exhibits smooth surface without any grains or crystallites indicating that the glass samples are not devitrified. SEM image and EDS spectrum of DP20 glass sample is shown in Fig. 3. The EDS profiles of

Conclusion

Lithium zinc phosphate glasses doped with Dy2O3 were prepared by melt quenching method. X-ray diffraction patterns confirmed the amorphous nature of the glasses. The thermal stability parameter for all the glasses is found to be greater than 100°C, which is an essential requirement to achieve fibre drawing. And the detailed thermal studies suggest that the prepared glasses have good thermal stability and are good materials for fibre fabrication. Structural units and the functional groups were

CRediT authorship contribution statement

M. Shwetha: Formal analysis, Investigation, Writing - original draft. B. Eraiah: Supervision, Conceptualization, Methodology, Validation, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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