Structural, Morphological and Photoluminescence Studies of Pure ZrO₂ and ZrO₂: Eu⁺³ Nanophosphors Synthesised by Microwave-Assisted Hydrothermal Technique

Abstract

The luminescence properties of pure and ZrO₂: Eu⁺³ nanophosphors with different concentration of the Eu⁺³ is synthesised and studied. A novel and environment benign microwave-induced hydrothermal process is used to synthesise the nanoparticles. As-formed pure ZrO₂ nanoparticles were X-ray amorphous, and upon calcination at higher temperatures, they crystallise to a combination of both cubic and tetragonal phases. However, the ZrO₂: Eu⁺³ nanophosphors prepared through the same technique under similar conditions yield exclusively cubic ZrO_2, and it entirely depends on the concentration of Eu⁺³ as revealed by XRD studies. The nanoparticles are found to be spherical, non-porous and agglomerated as observed by SEM. The surface area of the nanoparticles of pure ZrO₂ is found to be 30 m²/g for as-formed samples and 130 m²/g for calcined samples by BET studies. The increase in the surface area for calcined sample is due to the escaping of the adsorbed hydroxyl groups from the surface of the nanoparticles. The photoluminescence properties of the pure and Eu⁺³-doped ZrO₂ nanoparticles were measured under 251 nm excitation wavelength. Under this excitation, pure ZrO₂ gives the emissions at 394 nm, whereas Eu⁺³-doped nanoparticles gives the emissions at 613 nm, which corresponds to inter-f-f transition from ⁵D₀ ➔⁷F₂ (613 nm) and is arising due to electronic dipole in the Eu⁺³ activator ion. CIE colour space (x, y) coordinates corresponding to 613 nm in the CIE chromaticity diagram is 0.680, 0.319.