Optical, structural and morphological properties of Fe substituted rutile phase TiO₂ nanoparticles

Abstract

In present study, sol-gel derived Ti_(1-x)Fe_xO₂(0 ≤ x ≤ 10%) rutile nanoparticles were synthesized and their structural, optical and morphological characteristics were studied in detail. XRD showed the single rutile phase of Ti_(1-x)Fe_xO₂ nanocrystals without impurity. FTIR and Raman spectroscopic analysis also confirmed the single phase lattice structure without any impurity detection. SEM images showed the spherical nanoparticle formation in samples. The optical energy band gaps were calculated from UV-Diffusion reflectance spectra (DRS) data and Urbach energy was estimated for prepared samples. PL analysis showed the presence of O vacancies and defects. The present study enhance the understanding of structural, morphological and optical properties of Ti_(1-x)Fe_xO₂ rutile nanocrystals for potential application in optoelectronics, photocatalytic activity, solar cells and ceramics.

Introduction

Over the last few years, Titanium dioxide (TiO₂) has gained importance due to its specific dielectric, catalytic and optical properties which makes it suitable for many promising applications in the field of optoelectronics, photocatalytic activity, solar cells and ceramics [[1], [2], [3], [4]]. Titanium dioxide can be accessed in three polymorphs that are anatase (tetragonal), brookite (orthorhombic), and rutile (tetragonal). Amongst them, pure rutile phase is of special interest due to its high refractive index, chemical inertness, scattering efficiency, excellent light scattering effect and fabulous photocatalytic property. It can filter ultraviolet light due to its good scattering efficiency. It is widely used as a whitening agent in pigments and paints. The TiO₂ in rutile phase can be acquired through high-temperature calcinations of anatase nanoparticles. In earlier studies done by various groups, different techniques have been used to synthesize rutile phase nanoparticles [[5], [6], [7]]. Literature survey indicates that doping with variety of elements like Fe³⁺, V⁵⁺, Mn²⁺, Co³⁺, and Ni²⁺ enhances the performance of TiO₂ [2,[8], [9], [10], [11], [12]]. The Fe³⁺ ion has half-filled d-electronic configuration and has ionic radius of 0.64 Å [4]. Hence, Fe ion can integrate inside the TiO₂ lattice structure. Fe doping also enhances the conversion of n-type semiconductor nature of TiO₂ into p-type semiconductor. The existence of Fe³⁺ ion inside the TiO₂ crystal structure may stimulate rutile crystallization process. This improves the absorption intensity in UV–visible region [13].

Different techniques have been used for metal ion doping in TiO₂ such as sol-gel, wet chemistry, hydrothermal method, wet impregnation, co-precipitation method, microemulsion etc. Out of these, the sol-gel technique is a very simple handling and cost-efficient technique to prepare TiO₂ nanoparticles.

In present work sol-gel technique is used to synthesize for different Fe concentrations to investigate Fe doped TiO₂ rutile phase nanoparticles. Various properties like optical, morphological, and structural properties of Fe doped TiO₂ nanoparticles for concentrations of 0%, 1%, 5%, and 10% have been investigated. The material thus prepared is suitable for solar cells and photovoltaic applications. Here, in present research work, the defect states are studied in detail using PL analysis with modified optical band gap and structural properties which is not reported for single phase rutile TiO₂ nanoparticles as per our best knowledge. The novelty of this work is that significant band-gap reduction observed from the UV–Visible DRS results, which is supported by the analysis of PL results. In addition to this, the prepared materials may find prospective applications in optoelectronics, photocatalytic activity, solar cells and ceramics.