Photoluminescence and High Field Magneto-photoluminescence Spectroscopy of Phase Transformations in Semiconductors

Kalauni, Deepesh (2026) Photoluminescence and High Field Magneto-photoluminescence Spectroscopy of Phase Transformations in Semiconductors. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Deepesh Kalauni (19RS084)) 19RS084.pdf - Submitted Version Restricted to Repository staff only Download (17MB)

Abstract

This thesis demonstrates the use of photoluminescence (PL) spectroscopy as a versatile tool for probing both excitonic properties and structural phase transitions in semiconducting materials. While PL is traditionally employed to investigate electronic structure, carrier dynamics and exciton Bohr radii through magnetoPL techniques, this work demonstrates that temperature dependent PL measurements can also provide a sensitive, indirect optical alternative to structural probes such as X-ray diffraction for identifying phase transitions. A custom-designed, home-built fiber-coupled cryogenic system was developed and integrated with pulsed magnetic field capabilities up to 35 T, enabling magneto-optical measurements at temperatures down to 5 K and thus providing extreme conditions, which are typically accessible in specialized national facilities. We have investigated phenomena related to phase transitions in hybrid halide perovskites (MAPbI₃ and MAPbBr₃) and in CdSe nanoplatelets. In polycrystalline methylammonium lead iodide (MAPbI₃), magneto-photoluminescence measurements reveal a PL quenching above 250 K when the applied magnetic field exceeds a critical threshold. This quenching is reversible, is not observed in single-crystal samples, and shows recovery times of approximately one day. In CdSe nanoplatelets, temperature-dependent PL successfully identified a ligand layer phase transition near 250 K in the surface oleic acid coating, which correlates with a crossover between photobrightening and photodarkening behavior. The photodarkened state demonstrates thermal reversibility with an activation energy of approximately 55 meV. For MAPbBr₃ single crystals, dynamic hysteresis analysis of the structural phase transition revealed mean field universality characteristics, including scaling exponents of 2/3 and 1/3, along with ramp-reversal memory effects. Together, these results establish photoluminescence spectroscopy as a powerful dual purpose probe capable of revealing both microscopic excitonic physics and macroscopic phase transition dynamics, offering new insight into how external stimuli such as temperature and magnetic fields control optoelectronic responses in semiconductor systems.

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