Laser site-selective spectroscopy, Zeeman spectroscopy and crystal-field analysis of yttrium orthosilicate doped with Sm3+ and Er3+ ions

Abstract

Lanthanide-doped crystals are excellent candidates in the realisation of quantum information processing and communication devices. The ZEro First Order Zeeman (ZEFOZ) technique, which involves determining external magnetic fields at which the hyperfine structure is insensitive to magnetic field fluctuations in any direction, is the primary techniques used in the development of such devices. However, ZEFOZ points are notoriously difficult to find experimentally and are therefore required to be predicted through the use of, for example, a crystal-field Hamiltonian.

This thesis focuses on crystal-field modelling the 4f5 configuration of Sm3+:Y2SiO5, and refining the crystal-field model for the 4f11 configuration of Er3+:Y2SiO5. Temperature-dependent, Zeeman, Raman heterodyne and fluorescence spectroscopy was performed in order to determine the electronic and magnetic structure of both systems. The parameterised crystal-field models not only accurately reproduces the electronic, magnetic and low-field hyperfine structure of these systems, but is also able to predict polarisation and high-field hyperfine structure that was not fitted to in determining the crystal-field parameters. The parameter set for Sm3+:Y2SiO5 was scaled to fit to the electronic structure of Eu3+:Y2SiO5 and was able to predict the location of the ZEFOZ point of Eu3+:Y2SiO5 that was utilised in obtaining a six hour coherence time.

An understanding of the underlying dynamics of energy transfer is essential in the creation of efficient phosphors, white light emitting diodes and solar cells. Therefore, the energy transfer dynamics of Sm3+:Y2SiO5 was investigated through the use of site-selective laser spectroscopy. Intra-site energy transfer was found to proceed via a dipole-dipole mechanism for both sites. While the radiative decay rates were found to be insensitive to temperature for both sites, the energy transfer parameters were found to increase with temperature. Inter-site energy transfer from site 2 to site 1 was observed and became much stronger as the temperature increased. However, the reverse process, from site 1 to site 2, remained very weak at all temperatures.