Optical and Magneto-Optical Spectroscopy of Semiconductors and Upconverting Nanoparticles

Mukhuti, Kingshuk (2021) Optical and Magneto-Optical Spectroscopy of Semiconductors and Upconverting Nanoparticles. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Kingshuk Mukhuti (15RS072)) 15RS072_DPS.pdf - Submitted Version Restricted to Repository staff only Download (18MB)

Abstract

In this thesis, different aspects of halide perovskite semiconductors and lanthanide-doped upconverting nanoparticles are explored through techniques related to photoluminescence (PL) spectroscopy. Along with the regular low temperature PL experiments, we also describe the development of a magneto- PL system around a 35 T pulsed magnet in our laboratory. Such systems are thus shown to be practical for high-field magneto-optics in a small laboratory setting. A series of loosely connected problems on halide perovskite semiconductors (HPSs) are then studied with PL spectroscopy. A theoretical model, based on dissipative tunneling of the lead or tin ions is presented to explain a local symmetry breaking transition called emphanisis, and also consequently, the anomalous blueshift of the temperature-dependent bandgap in chalcogenides and HPSs. The lowand the high-energy tails of the PL spectra in the perovskite CsPbBr₃ nanosheets are studied next. It is shown that they contain information regarding the exciton localization, thermalization, and excitonphonon scattering. A framework of Urbach edge analysis based on the PL spectra is developed and the full Urbach rule, including the existence of the Urbach focus, is demonstrated. Finally, the excitonic features (Bohr radii and binding energies) in hybrid HPs [FAxMA(₁₋x)PbI₃ series] are comprehensively investigated through magneto-optics in their different crystallographic phases. In the second part of the thesis, we study problems related to PL-upconverting Yb³⁺-Er³⁺ nanoparticles, codoped with NaGdF₄. First, the partially overlapped intra-4f transitions that constitute the extremely complicated emission spectrum of Er³⁺ ions are classified through a novel approach of twodimensional correlation analysis, avoiding involved quantum mechanical calculations. Next, the multiphoton pathways for the Er³⁺by varying temperature and excitation power, reveal the increased importance of three-photon mechanisms at low temperature. This information enables the prediction regarding the failure of a Boltzman-type ratiometric thermometer at low temperature. As an alternative, a colorimetric thermometer based on the non-thermally coupled transitions is proposed. We next study the PL emission in high magnetic fields. Motivated by the B²-dependent suppression-upconversion, studied of PL intensity under magnetic fields (B), we present a quantum electrodynamics calculation for the magnetic field dependent change in the efficiency of the F¨orster resonance energy transfer process to corroborate the experimental findings. Finally, the spatial and spectral coherence properties of the two-colour emission spectrum from Er³⁺ ions are studied via the Young’s double-slit interference of the PL emission.

Actions (login required)

View Item