Development and Implementation of Cryogenic optical setup for low temperature Raman and Photoluminescence Studies

Mazumder, Aritra (2019) Development and Implementation of Cryogenic optical setup for low temperature Raman and Photoluminescence Studies. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Aritra Mazumder (14MS109)) 14MS109.pdf - Submitted Version Restricted to Repository staff only Download (13MB)

Abstract

Low-temperature Physics is one of the cornerstones of condensed matter physics. Some of the most well known phenomena such as Superconductivity, super-fluidity Quantum Hall effect, etc and most of the quantum many-body phenomena, take place at very low temperatures. In this work we have mostly dealt with low temperature, temperature dependent and high-pressure Raman and Photo Luminescence (PL) study. Raman modes of a material is directly related to it's vibrational spectrum and hence to it's structure, thus allowing us to study structural phase transitions and use it to identify compounds. Also, we can look at the different phonon coupling with electrons, spins or magnons by studying the changes in Raman spectra under different conditions of pressure, temperature and external magnetic fields. PL spectra can be used to study the dynamics of electronic states, band gaps and defects. During the length of this thesis, we have worked on developing a temperature dependent optical setup. We have calibrated the system using Sulfur and Silicon and we have found reported phase transitions in Cs₃Bi₂Br₉ systems at 95K. Analysis of the temperature dependent Raman spectra has allowed us to study the an-harmonic contributions of the potential, electron-phonon coupling, spin-phonon coupling and effect of thermal expansion on the vibrational states. We have also seen changes in Raman spectra of Cs₃Bi₂Br₉ at around 60K and 30K which has been previously unreported. We have prepared rare earth titanate using laser quenching and normal solid-state synthesis method and we have carried out temperature dependent and pressure dependent Raman and PL studies on Rare Earth titanate, we see a possible phase transition around 8GPa. In the temperature dependent Raman data we see deviation from expected behaviour at 30K and 40K for Gd based and Er based Titanates. The possible causes have been discussed as well as the effect of oxygen vacancy and self trapped excitations in the PL has been studied in this work.

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