Synthesis of Nd3+doped TiO2 nanoparticles and Its Optical Behaviour

Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

Synthesis of Nd3+doped TiO2 nanoparticles and Its Optical Behaviour3 Ezhil Arasi S.1,a, Victor Antony Raj M1, Madhavan J. 1 1 – Department of Physics, Loyola College, Chennai-34, India a – jmadhavang@gmail.com DOI 10.2412/mmse.21.46.481 provided by Seo4U.link

Keywords: sol-gel method, optical studies, energy transfer.

ABSTRACT. Pure and Rare earth ion doped TiO2 nanoparticles were synthesized by Sol-gel method. The synthesized TiO2 nanoparticles were characterized by X-ray diffraction, Raman spectroscopy, UV–Vis spectroscopy and photoluminescence emission spectra. From the UV-visible measurement, the absorption edge of Nd3+-TiO2 was shifted to a higher wavelength side with decreasing band gap. Photoluminescence emission studies reveal the energy transfer mechanism of Nd3+ doped TiO2 nanoparticles explain.

Introduction. In the recent years, remarkable progress has been achieved in synthesis and characterization of titanium dioxide (TiO2) nanostructures due to their unique physical and chemical properties leading to extensive use as sensing materials, photo catalyst, H2 storage and electrode materials [1]. Compounds doped with rare earth ions have received considerable interest in both fundamental and application studies due to their significant technological importance and are used as high performance luminescent devices, solar cells, solid-state lasers, time-resolved fluorescence labels for biological detection and other functional applications. As a host material, TiO2 is considered as a promising semiconductor with outstanding optical properties [2]. Due to wide band gaps, TiO2 is an important applicant for UV light absorption and is almost transparent for infrared (IR) and visible light. It is a known fact that when dopants are added to a semiconductor they introduce band gap states inside the band gap and these mid-states act as luminescent centers or nonradiative traps.

Because of the effective emission in the visible and near IR region, doping of TiO2 with rare earth elements has attracted much attention [3].

Synthesis of TiO2 nanoparticles. Pure and doped TiO2 samples were synthesized by a sol-gel method. 5ml of Titanium (IV) isopropoxide was added drop wise under vigorous stirring into 30ml of isopropanol. This mixture was added drop wise into 30ml of distilled water under stirring. The final pH was adjusted with an aqueous solution of ammonia. The mixture was left for 24 hours at room temperature to complete the hydrolysis. The precipitate was dried at 100˚C for 1 hour and the resultant white powder was milled. The obtained samples were centrifuged in distilled water and ethanol three times in order to remove any impurities and further calcinated at 400˚C for 3hours.

The metal ion doped TiO2 nanoparticles were synthesized using the same technique as described above. The Nd compound of Nd2O3 was used as a dopant source.

Result and Discussion: X-Ray Diffraction Study. The synthesized TiO2 nanoparticles were characterized by a X-ray Diffractometer with monochromatic CuK (=1.5406 Å) and taken over the 2 range 20 – 70 by 3

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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

step scanning with a step size of 0.05. The strongest peak for the anatase (101) phase of TiO2 was used to determine the average size of the metal oxide nanocrystallites using Scherer’s equation,

D=

where D – crystallite size; K is the constant of 0.9; λ is the wavelength of X-Ray; β is the full width at half- maximum (FWHM) of the selected peak and θ is the Bragg’s angle of the diffraction of the peak.

Fig. 1. XRD patterns of pure and Nd3+ doped TiO2 nanoparticle.

Fig. 1 shows XRD pattern of pure and Nd3+ doped TiO2 nano particles respectively. The diffraction peaks corresponding to 2θ values are identified as (1 0 1), (1 1 2), (2 0 0), (1 0 5), (1 2 1), (2 0 4) and (1 1 6) and it matches well with the diffraction pattern of bulk anatase Titania peaks. XRD patterns are matched with the standard XRD pattern of TiO2 (JCPDS file No: 21-1272).

The peaks at 2θ correspond to the (1 0 1), (0 0 4), (2 0 0), (1 0 5), (2 1 3) and (2 1 3) planes of TiO2:Nd3+ nanoparticles. The average crystalline sizes of pure and doped TiO2 nano particles were in the range of 15 - 25 nm.

UV characterization. UV-Vis absorption Spectra was recorded by using Varian Cary 5E spectrophotometer. The UV-Vis spectral analysis was carried out between 200 nm and 800 nm.

Fig. 2. UV-Vis absorption spectrum of pure and Nd3+: TiO2 nanoparticles.

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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

The plot between the absorption coefficient and wavelength is as shown in Fig. 2 for pure and doped TiO2 nanoparticles. The knee edge at 360 nm in the spectrum shows a shift compared to its bulk counterpart which is nearly 50 nm, due to the weak quantum effect occurred during the growth process.

The absorption spectra of Nd3+. TiO2 nanoparticle reveals sharp absorption edge observed at 395nm. The presence of Neodymium had shifted the absorption edge by 35nm from the undoped TiO2.

FT-Raman analysis. Fig. 3 shows the FT-Raman spectra of pure and doped TiO2 nanoparticles synthesized via sol-gel method in the range of 100–800 cm−1. The FT-Raman spectrum was recorded using BRUKER IFS–66V spectrometer.

Fig. 3. FT-Raman spectrum of the pure and Nd3+: TiO2nanoparticles.

The Raman spectrum of the pure TiO2 shows peaks at 143.6 cm-1, 194.2 cm-1, 395.5 cm-1, 515.7 cm-1 and 638.7 cm-1, which can be assigned to the anatase phase [4]. The spectra of Nd3+:TiO2 nanocrystals are similar to that of anatase but being slightly shifted as a result of crystal structure modification via doping. The Raman spectrum of Neodymium trivalent ion doped TiO2 (Fig. 4.14) shows peaks at 144.76 cm-1, 147.76 cm-1, 398.68 cm-1, 517.93 cm-1 and 639.24 cm-1.Thus from the Raman studies we can confirm that the anatase phase was not altered by the presence of trivalent lanthanide dopants.

Photoluminescence (PL). The photoluminescence spectrum of pure TiO2 nanoparticles was recorded in the spectral range of 490-550nm. The peak positioned at 515 nm of the pure TiO2 is due to the radiative annihilation of the exciton after excitation at 330 nm.

4 The PL spectra of 4F3/2 IJ belonging to f-f transition of the trivalent Nd ion in TiO2: Nd nanoparticles are shown in Fig. For the excitation wavelength of 350nm, Two main PL peaks were found at 1095nm and 1366nm. In the prominent transitions are 4F3/2 4I11/2 and 4F3/2 4I13/2 lying at 1095 nm and 1366nm is due to the f-f transitions of Nd3+ [5, 6].

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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

Fig. 4.Photoluminescence spectrum of pure and Nd3+ TiO2 nanoparticles.

Summary. The successfully prepared TiO2, Nd3+ doped TiO2 samples were subjected to various optical studies. From XRD results, it is clear that synthesized pure and doped Titania nanoparticles exhibited the anatase structure. From the optical absorption spectrum, a significant spectral shift in the wavelength is observed as compared to bulk TiO2 crystal. The broadening of absorption edge is the result of absorption of nanocrystallites with distribution of anatase nanoparticles at different size regime. The presence of trivalent lanthanide ions had resulted in shifting of the absorption edge towards the visible region.

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Cite the paper Ezhil Arasi S., Victor Antony Raj M, Madhavan J. (2017). Synthesis of Nd3+doped TiO2 nanoparticles and Its Optical Behaviour. Mechanics, Materials Science & Engineering, Vol 9. doi:10.2412/mmse.21.46.481

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