Temperature dependent optical studies of Ti$_{1-x}$Co$_x$O$_2$

TL;DR

This study investigates how temperature affects the optical properties of Co-doped TiO$_2$ thin films, revealing dopant-related emission features and confirming the anatase phase through Raman and PL analyses.

Contribution

It provides new insights into the optical behavior and phase stability of Co-doped TiO$_2$ films across different doping levels and temperatures.

Findings

Doped films exhibit a broad STE emission at 2.3 eV below 120 K.

Co doping introduces new emission lines at 2.77 eV and 2.94 eV.

The anatase phase is confirmed in all films via Raman spectroscopy.

Abstract

We present the results of Raman and photoluminescence (PL) studies on epitaxial anatase phase Ti$_{1-x}$Co$_x$O$_2$ films for $x$ = 0-0.07, grown by pulsed laser deposition. The low doped system ($x$=0.01 and 0.02) shows a Curie temperature of ~700 K in the as-grown state. The Raman spectra from the doped and undoped films confirm their anatase phase. The photoluminescence spectrum is characterized by a broad emission from self-trapped excitons (STE) at 2.3 eV at temperatures below 120 K. This peak is characteristic of the anatase-phase TiO$_2$ and shows a small blueshift with increasing doping concentration. In addition to the emission from STE, the Co-doped samples show two emission lines at 2.77 eV and 2.94 eV that are absent in the undoped film indicative of a spin-flip energy.