Wide Band Gap Oxides as the Probes for Optical Based Sensing Applications

Abstract

Temperature is a very critical and widely measured variable by both researchers and engineers. In this regard, most of the available temperature sensors are based on contact mode of operation. In this consideration, the optical based sensing being a non-contact mode of sensing has advantages of fast response, noninvasive and inertness to electro-magnetic environments. Among different available optical based sensing, the most popular methods are Raman and photoluminescence (PL) spectroscopy-based sensing due to their own advantages for wide range of detection. Among various materials, here, wide band gap oxides have been exploited as the probes for temperature sensing based on Raman and PL spectroscopy. It has been shown that temperature can be evaluated using the variation of intensity ratio between two Raman peaks of In2O3 with temperature. Similarly, the PL based temperature sensing relies on the variation of the peak position, single emission intensity and ratio between two intensities with temperature. In the case of ratiometric sensing case, the ratio between two emissions from thermalized levels of Er and Eu ions, where the energy separation between the levels is order of thermal energy is considered. A dual emission where one intensity increases followed by decrease in the other with increase in temperature of EuEr:ZnO microrods is taken into consideration. In the last part, the effect of host and excitation on the PL emission for temperature sensing is analyzed by taking Eu:In(OH)3/In2O3 as an example. Picric acid is a serious environmental pollutant generated from leather, pharmaceutical, chemical and dye industries. As it easily contaminates groundwater owing to the high solubility and is liable for irritation to the skin/eye and potential damage to respiratory organs, its detection is of paramount importance. The last section of the thesis deals with the detection of nitro aromatic compounds in solid state employing MgO nanocubes as optical probes