Abstract
Uniform, spherical-shaped TiO2:Eu nanoparticles with different doping concentrations have been synthesized through controlled hydrolysis of titanium tetrabutoxide under appropriate pH and temperature in the presence of EuCl3·6H2O. Through air annealing at 500°C for 2 h, the amorphous, as-grown nanoparticles could be converted to a pure anatase phase. The morphology, structural, and optical properties of the annealed nanostructures were studied using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy [EDS], and UV-Visible diffuse reflectance spectroscopy techniques. Optoelectronic behaviors of the nanostructures were studied using micro-Raman and photoluminescence [PL] spectroscopies at room temperature. EDS results confirmed a systematic increase of Eu content in the as-prepared samples with the increase of nominal europium content in the reaction solution. With the increasing dopant concentration, crystallinity and crystallite size of the titania particles decreased gradually. Incorporation of europium in the titania particles induced a structural deformation and a blueshift of their absorption edge. While the room-temperature PL emission of the as-grown samples is dominated by the 5D0 - 7Fj transition of Eu+3 ions, the emission intensity reduced drastically after thermal annealing due to outwards segregation of dopant ions.
Highlights
Luminescent nanomaterials have gained considerable attention in recent years due to the breakthrough developments of technology in various areas such as electronics [1,2], photonics [3], displays [4,5], optical amplifications [6], lasers [7], fluorescent sensing [8], biomedical engineering, [9] and environmental control [10]
We report the incorporation of Eu +3 ions in TiO2 nanoparticles by a simple and versatile sol-gel technique which could be extended to different lanthanide and transition metal ions in order to obtain multifunctional materials
When the sample is annealed at 500°C, all the PL emissions almost disappeared (Figure 10). This could be related to the transformation of amorphous titania to a fully crystalline anatase phase which presents a higher density, making more difficult for Eu+3 ions to locate at the site of Ti+4 due to the large difference in their ionic radii [42]
Summary
Luminescent nanomaterials have gained considerable attention in recent years due to the breakthrough developments of technology in various areas such as electronics [1,2], photonics [3], displays [4,5], optical amplifications [6], lasers [7], fluorescent sensing [8], biomedical engineering, [9] and environmental control [10]. For the application in luminescent devices, small phosphor particles of a spherical morphology, narrow size distribution, and low dispersity are desired to improve their emission intensity and screen packing [21]. To meet these demands, a variety of synthesis methods have been applied to fabricate RE-doped titania nanoparticles. The particles obtained have shown a perfectly spherical shape, improved size distribution, and excellent luminescent characteristics, elucidating the possibility of applying RE-doped titania nanoparticles as an efficient luminescent material. PL measurements were performed at room temperature using a Jobin Yvon iHR320 spectrometer (HORIBA) with a 374-nm emitting diode laser as an excitation source
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