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In this paper we report the deposition of TiO2:0.07Eu3+ thin films by sol gel spin coating technique and effect of annealing temperature on enhancement of red-light emission efficiency. The crystalline structure and phase formation of TiO2:0.07Eu3+ nanophosphors were investigated by an X-ray diffraction analysis. The TiO2: 0.07Eu3+ coatings had a wide direct band gap (3.75eV) and high refractive index (2.19). Raman spectroscopy was also employed to identify the phase formation and vibrational modes present in the TiO2:0.07Eu3+ thin films. The phonon energy was calculated using excitation spectrum and complemented well with the vibrational modes in the Raman spectrum. Under 394 nm excitation, the anatase TiO2:0.07Eu3+ nanophosphors exhibited strong luminescence emission due to f–f transitions of Eu+3 and dominant red emission was the hypersensitive 5D0 →7F2 transition. The photoluminescence (PL) emission intensity as a whole is observed to increase as the annealing temperature is increased. Radiative transition rates, fluorescence branching ratio, stimulated emission cross section and radiative decay lifetime were carried out with Judd-Ofelt analysis. The experimental lifetime was obtained by the double exponentially fitted decay curve of the 5D0 level monitoring emission at 614 nm and excited by 394 nm. The chromaticity coordinate values (0.65, 0.35) were estimated using International Commission International de l’Eclairage (CIE) 1931 system, which is close to the National Television Standard Committee (NTSC) red phosphor chromaticity coordinate values. The photodegradation efficiencies of TiO2:0.07Eu3+ thin films increase with an increase in the annealing temperature for the degradation of methyl blue under visible light irradiation.
Key words: TiO2:0.07Eu3+ thin film, band gap energy, Refractive index, Raman modes, photoluminescence, j-o parameters, Color Coordinates and photocatalytic activity.
During the last few decays Titanium dioxide (TiO2) has been widely studied because of its potential applications in optoelectronic devices including photocatalysis, photochromic devices, optical waveguides, optical amplifiers, anti-reflection coatings, dye-sensitized solar cells, sensors, biocompatible materials [1-13]. Recently many researchers have been focused to explore TiO2 based nanophosphors doped with different rare earth (RE) ions as an ultimate luminescence materials, because of their unique luminescence features such as sharp emission peaks originating from the electronic transition between f levels, large Stokes shift and long decay time [14-17]. Among the various RE ions dopants, the trivalent europium (Eu3+) ion exhibit high color purity and luminescence efficiency [17-20]. Luminescence emission is high sensitive to the coordination environment of Eu3+ ion, due to this reason, Eu3+ ion has been used as a spectroscopic probe of local site structure in metal oxide matrices . Titanium dioxide (TiO2) is considered as a promising transition metal oxide semiconductor material owing to its interesting properties including the high stability, water insoluble, excellent oxidation capacity, high photosensitivity, resistance to corrosion, bio-compatibility, nontoxic and environmental friendly . These excellent properties make TiO2 as a promising material for photocatalysis. Also the TiO2 doping with Eu3+ ions proved to be an effective process to enhance the photocatalytic properties of TiO2 due to extended the absorption of TiO2 into the visible region and the formation of oxygen vacancy charge trapping centers leading to a decrease of electron/hole recombination rate.
Nowadays TiO2: Eu3+ has attracted much attention because of its use as a luminescent material and as an efficient photocatalyst. Numerous techniques such as magnetron sputtering [21, 22], pulsed-laser deposition , spray pyrolysis , sol-gel method [25-31], hydrothermal method , and electrospining [33, 34], have been employed for the synthesis of the Eu3+ doped TiO2. In this paper, we have applied sol gel spin coating for the synthesis of TiO2:Eu3+ thin films due to its simplicity, low cost and capability to produce nanostructured materials, having high quality, transparent and homogenous films of different compositions on various substrates.
In this article, our interest is focused on synthesis of Eu3+ doped TiO2 nonoparticles and to study the effect of annealing temperature on structural and spectroscopic properties as well as its photocatalytic activity. We have prepared TiO2:0.07 Eu3+ thin film nanostructures that behave as an efficient photoluminescence and photocatalytic activity by modified sol-gel spin coating. The intensity parameters (Ω2, Ω4) and various other radiative parameters have been calculated through Judd− Ofelt theory, which is helpful in understanding the coordination environment of Eu3+ in the TiO2 matrix. Moreover, the photocatalytic performances of TiO2:0.07Eu3+ was evaluated by using MB as a representative dye pollutant under visible light irradiation.
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