Optical holeburning in colour centres

Abstract

The thesis deals mainly with the spectroscopic investigation of colour centres in solids using high resolution of the optical holeburning technique. Though frequent use has been made of conventional spectroscopic techniques such as absorption, emission, laser excitation and the magnetic circular dichroism spectroscopy, such experiments were performed either as preliminary investigations before holeburning techniques or were needed to compliment the data obtained from the high resolution techniques. Therefore, only a brief and necessary account of such experiments is presented. Chapter I is a basic introduction to holeburning spectroscopy. An account is also given of the two laser holeburning which has been utilized in the later part of the thesis to investigate N-V colour centre in diamond. Chapter II deals with the experimental details of the techniques utilized in the studies but by no means is exhaustive, as some techniques have been described later on in the relevant chapters. Chapter III deals with the holeburning in CaO:F centre. It has been shown that high resolution Zeeman measurements can be performed on the optical hole in the zero phonon line of the F centre with very low fields. The Zeeman measurements confirm the interpretation of the previous ODMR studies on this system. Results have also been presented for the stark effect on this centre and the phonon broadening of the holes. In both of these instances our results differ from the previous reports which concentrated mainly on low resolution techniques. Holeburning in this centre is proposed to be photochemical and the holeburning characteristics are discussed. Chapter IV deals with the holeburning in the N-V centre in diamond where there is a short lived hole. A very detailed spectrum is obtained by using two lasers- one to burn and another to read. Two laser holeburning data has been crucial in revising the assignment of the zero-phonon line of the N-V centre. Previous optical ODMR and single laser holeburning studies have not been able to correctly assign the multiplicity of the states involved. Revised assignment on the basis of two laser holeburning has been further checked by different techniques such as the optical- microwave double resonance, Zeeman studies on the antiholes and the temperature dependence of magnetic circular dichroism. All these measurements have been found to support the proposed assignment. The latter part of the chapter presents a model for holeburning in a ³A —>³E transition and it is showm that by considering spin-orbit and strain a spectrum similar to that observed can be predicted. Chapter V briefly deals with the other colour centre systems where some preliminary holeburning measurements suggested that a detailed investigation of such systems would require circumventing some technical problems, such as control on the production of the desired centre, with needed concentrations. Some suggestions are made to further advance in these directions. Show more