# Structural, Morphological and Optical Characterization of Eu 3+ and Nd 3+ Co- Doped Tio2 Nano Particles by Sol Gel Method

S Sanjay, K Deepa, M Victor Antony Raj, S Senthil

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S Sanjay, K Deepa, M Victor Antony Raj, S Senthil. Structural, Morphological and Optical Characterization of Eu 3+ and Nd 3+ Co- Doped Tio2 Nano Particles by Sol Gel Method. Mechanics, Materials Science & Engineering Journal, 2017, 9, 10.2412/mmse.77.97.901. hal-01499402

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# Structural, Morphological and Optical Characterization of Eu³⁺ and Nd³⁺ Co-Doped TiO₂ Nano Particles by Sol Gel Method

P. Sanjay¹, K. Deepa², M. Victor Antony Raj², S. Senthil¹, a

1 – Department of Physics, Government Arts College for Men (Autonomous), Chennai, India

2 – Department of Physics, Loyola College, Chennai, India

a – ssatoms@yahoo.co.in

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DOI 10.2412/mmse.77.97.901 provided by Seo4U.link

**Keywords:** co-doped TiO₂ nanoparticles, XRD, UV-Vis, HRTEM, FTIR.

**ABSTRACT.** Semiconductor nano crystals have been widely studied for their fundamental properties. The Eu³⁺ and Nd³⁺ doped titanium dioxide nano powder was successfully synthesized by sol-gel method. The morphological and structural properties of as-prepared samples were characterized by X-ray diffraction (XRD), High Resolution Transmission Electron Microscope (HRTEM). The Powder X- ray diffraction is carried out in order to examine the phase formation and substitution of Eu³⁺ and Nd³⁺ doped in TiO₂ matrix. The UV-Vis spectral analysis was carried out between 200 nm and 1200 nm. The band gap of the Eu³⁺ and Nd³⁺ doped Tio₂ nanoparticles was calculated. The functional groups of the synthesized compound have been identified by FTIR spectral analysis. The strong PL intensity confirms a blue shift.

**Introduction.** Titanium dioxide (TiO₂) nanomaterials are used in a wide range of applications such as photo catalysis, sensor devices, paints and dye-sensitized solar cells. The material properties of TiO₂ nanoparticles depend upon the parameters like crystal structure, nanoparticle size and morphology. However, these parameters are depending on the method of synthesize [1]. Titanium dioxide exists in three main crystallographic forms of anatase, rutile and brookite [2]. Among the various polymorphs listed above, anatase type has been selectively used for photocatalytic applications and various other applications [3]. Sol-gel method was often employed to prepare TiO₂ because of its simplicity and low equipment requirement. The conventional sol-gel process usually involved uncontrollable fast hydrolysis and condensation and therefore could result in formation of amorphous TiO₂ [4]. Sometimes, the high temperature would seriously affect the particle size and surface area and even could result in a collapse of the mesoporous structure. Therefore, it is necessary to synthesize nanocrystalline anatase under mixed conditions. Many researchers have tried to prepare nanostructure anatase TiO₂ in well crystalline form. Some researchers have reported that they could improve the absorption and photocatalytic activity via dye sensitizing, surface deposition with metal or doping with metal, nonmetal, or their oxides. Many nonmetal ions have been successfully doped the intensity of photoluminescence (PL) of TiO₂ doped with Sm³⁺ ions was reported to show specific dependence on the oxygen content in the surrounding atmosphere and similar effects have been seen in case of Eu³⁺ doped titania and also in the intrinsic emission of porous TiO₂ [5-7]. This motivates further work to elaborate photoluminescent gas sensing materials based on lanthanide doped TiO₂. It is very necessary for researchers to explore the theory and the experimental results on such field. In the present work, we have synthesized anatase phase of Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles by sol-gel method and they were analyzed for structural and optical properties.

## EXPERIMENTAL DETAILS
**Synthesis procedure.** Pure Titanium dioxide nanocrystals were prepared using the sol-gel method. Titanium isopropoxide (TIP) was used as the precursor for Titania sol preparation. The sol corresponds to the overall volume ratio of Ti [OCH(CH₃)₂]₄: C₃H₈O: CH₃COOH: Distilled H₂O = 5:30:4.4:30. Ti [OCH(CH₃)₂]₄ was first dissolved in isopropanol and distilled water to form titania sol and then stirred for 1h at room temperature. The pH of sol was adjusted to 2-3 by adding 1-2 drops of ammonia with stirring in room temperature for 12h. The prepared sol was left to stand for the formation of gel and dried at 100°C for an hour in a furnace to remove the solvents. The obtained gel was milled into powders and calcined at 400°C for 4h to keep anatine TiO₂ phase. Europium and neodymium co-doped TiO₂ was synthesized using the same procedure as the reference sample.

## RESULT AND DISCUSSION

**XRD Analysis.** The XRD pattern of the Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles are shown in Fig.1. The Strong and sharp peaks of the pattern confirmed the crystalline structure of the samples. All theme main diffraction peaks at 25.38 (101), 37.96 (002), 48.04 (042), 55.94 (361) and 63.20 (211) coincide with the JCPDS values (PDF Card No: 21-1272) which correspond to crystal structure of anatase. The variation in intensity of the diffraction peaks indicates the crystallinity behavior due to lattice distortion. When Nd³⁺ and Eu³⁺ ions are incorporated into the periodic crystal lattice of TiO₂, a strain is induced into the system, resulting in the alteration of the lattice periodicity. Furthermore, after doping, the diffraction peaks got broadened suggesting a systematic decrease in the crystallite size. The crystallite size of the co-doped nanoparticle were estimated from the most intense peak based on Scherer equation D = kλ/βcosθ where k is the shape factor taken as 0.9, λ is the wavelength, β is full width at half maximum and θ is the diffraction angle. Average crystallite size in co-doped TiO₂ matrix was calculated as 25.50 nm.

<figure><img src="image_3.png" /><figcaption>Fig. 1. XRD pattern of Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles.</figcaption></figure>

**Optical Properties.** The synthesized Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles were analyzed by UV-Vis absorption spectroscopy as seen in Fig. 2 (a). The absorbance of the nanoparticles exhibits a sharp decrease in the visible region (380 nm); co-doping of Nd³⁺ and Eu³⁺ can have significant influence on the absorption of light. The cut-off wavelength has been enlarged to the visible regions by doping. The cut-off wavelength shifted from 380nm by increasing with Nd³⁺ and Eu³⁺ content. The result shows that the range of light absorption of doped TiO₂ is wider than undoped TiO₂ nanoparticles, also optical band-gap measurements of the prepared sample were carried out. The band gap for Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles was calculated using the formula:

$$ahv = C (hv-Eg)^{1/2}$$
where $\alpha$ is absorption coefficient, C is a constant, $h\nu$ is energy of photons and $E_g$ is the energy band gap.

By plotting $(a\hnu)^2$ versus 'h$\nu$' the value of the band gap was found to be 3.02 eV for co-doped $TiO_2$ nanoparticles. Fig. 2 (b) shows the band gap plot of the $Nd^{3+}$ and $Eu^{3+}$ co-doped $TiO_2$ nanoparticles. As the $Nd^{3+}$ and $Eu^{3+}$ doping ratio is increasing the band gap values decreased. These band gap and absorbance spectra supported each other. These results prove that doping can reduce the wideness of forbidden band of $TiO_2$ nanoparticle.

<figure><img src="image_4.png" /><figcaption>Fig. 2. (a) UV-vis absorption spectra of the $Nd^{3+}$ and $Eu^{3+}$ co-doped $TiO_2$ nanoparticles.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>Fig. 2. (b) Optical band gap ($E_g$) spectra of the $Nd^{3+}$ and $Eu^{3+}$ co-doped $TiO_2$ nanoparticles.</figcaption></figure>

## HRTEM Analysis

HRTEM allows the direct imaging of nanoparticles and provides authentic information on the distribution, size and morphology of the nanocrystalline. The morphology of the synthesized products was investigated by HRTEM analysis. Fig. 3 shows the HRTEM images of $Nd^{3+}$ and $Eu^{3+}$ co-doped $TiO_2$. From the Fig., it is observed that most of the particles are almost spherical in shape with uniform size distribution. However, on $Nd^{3+}$ and $Eu^{3+}$ co-doping the size of the particles is increased in spherical morphology.
<figure><img src="image_6.png" /><figcaption>Fig. 3. HRTEM image of the Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles.</figcaption></figure>

## Photoluminescence (PL)

The PL spectra of Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticle are shown in Fig.4. PL emission spectra have been widely used to investigate the efficiency of charge carrier trapping and migration and to understand the fact of electron-hole pairs in semiconductors. As shown in Fig., three emission peaks are observed for Nd³⁺ and Eu³⁺ co-doped TiO₂. Among the three peaks one is large intense positioned at 380 nm. The peak at 380 nm is band edge luminescence of TiO₂ nanoparticle and other two less intense peaks are positioned at 363 and 424 nm respectively. These emission bands originated from charge recombination at the shallow-trap surface state. This surface state originated from the oxygen vacancies which act as radioactive centers. However, in Nd³⁺ and Eu³⁺ co-doping the above stated three peaks are largely blue shifted to 363, 380 and 424 nm as a result of doping.

<figure><img src="image_7.png" /><figcaption>Fig. 4. PL spectra of the Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles.</figcaption></figure>

### Fourier Transform Infrared Spectroscopy (FT-IR)
FTIR spectroscopy is used to identify and characterize the organic species present in the Nd³⁺ and Eu³⁺ co-doped TiO₂ nanostructured materials. The FTIR spectra of the as prepared Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles is shown in Fig.5. The two weak absorption bands around 2043 cm⁻¹ and 2984 cm⁻¹ are due to C-H symmetric stretching of organic residue. The weak peak that appeared at 1124 cm⁻¹ and 1082 cm⁻¹ in Nd³⁺ and Eu³⁺ co-doped sample is associated to the asymmetric stretching vibration modes of Ti-O networks. The peaks observed at 3600-3000 cm⁻¹ is assigned to -OH of water absorbed from the molecular precursors. The band at 3000-2750 cm⁻¹ may be due to symmetrical stretching vibration of -CH₂
groups. The peaks 1530–1260cm⁻¹ indicates asymmetrical and symmetrical CH₃ deformation vibrations from titanium-isopropoxide and C–C–O stretching vibration is positioned at 1130–820cm⁻¹ from ethylene glycol. Thus the FTIR spectra confirm the presence of functional groups and their mode of vibrations.

<figure><img src="image_8.png" /><figcaption>Fig. 5. FTIR spectra of the Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles.</figcaption></figure>

**Summary** We have successfully synthesized the Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles by sol-gel method at room temperature. The XRD pattern depicted the structure and grain size of the Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles. The UV-DRS spectra of Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles showed an absorption peak at 380 nm in the UV region. In the co-doped TiO₂, considerable blue shift was obtained for all the samples due to quantum confinement effect. The band gaps were found to be 3.02 eV on increased doping concentration doping band gap energy has been decreased. The various functional groups present in the material have been determined by FTIR analysis. The morphology of the products revealed spherical structure of Nd³⁺ and Eu³⁺ co-doped TiO₂ nanoparticles which characterized using High Resolution Transmission Electron Microscopy (HRTEM). The PL emission spectra revealed the structural modification of the TiO₂ matrix with doping by Nd³⁺ and Eu³⁺ ions, as well as the change in the charge transfer pairs on the surface of TiO₂.

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Cite the paper

P. Sanjay, K. Deepa, M. Victor Antony Raj, S.Senthil (2017). *Structural, Morphological and Optical Characterization of Eu3+ and Nd3+ Co-Doped Tio2 Nano Particles by Sol Gel Method*. *Mechanics, Materials Science & Engineering*, Vol 9. doi:10.2412/mmse.77.97.901