Mr. Debojyoti Ray Chawdhury Profile

Debojyoti Ray Chawdhury

at Indian Institute of Technology Madras

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Proceedings Article | 10 June 2024 Poster + Paper

Resonant and non-resonant microcavity effects on nitrogen vacancy centres

Debojyoti Ray Chawdhury, Tulika Agrawal, Prem Bisht

Proceedings Volume 12991, 129911K (2024) https://doi.org/10.1117/12.3014208

KEYWORDS: Microspheres, Whispering gallery modes, Optical microcavities, Nitrogen, Electric fields, Raman scattering, Raman spectroscopy

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Nitrogen Vacancy (NV) centres in nanodiamonds (NDs) are excellent fluorophores. They find applications in bio-sensing, bio-imaging and as single photon emitters. The photoluminescence (PL) spectra of NV centres span over the visible-near IR region (500-900 nm). The spectra consist of temperature-dependent sharp characteristic peaks of neutral and negatively charged NV centres corresponding to Zero Phonon Line (ZPL) transition. When these NV centres are coupled with microcavities, sharp ripple-like resonant modes known as Whispering Gallery Modes (WGMs) are observed in the emission spectra. The time-resolved fluorescence of NV centres are found to be dependent on excitation and emission energies. The fluorescence decay of NV centres reveals the contribution of different charge states. In addition, jet-like structures (photonic nanojet, PNJs) are observed due to the non-resonant interaction of light and NV centre-coupled microcavity. The PNJs have been used to enhance the weak Raman scattering signal.

Proceedings Article | 17 April 2024 Poster

Study of surfactant assisted isolated crystalline pyrene coupled microcavity

Shruti Narayanan, Debojyoti Ray Chawdhury, Prem Bisht

Proceedings Volume 13108, 131080Z (2024) https://doi.org/10.1117/12.3030488

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Fluorescence spectrum of pyrene molecule in solution form has been of interest in the research community for more than six decades. Sensitivity of these molecules to solvent polarity makes them active probes for sensing impurities. Pyrene molecules when excited form an excimer complex with another molecule in the ground state, typically by the pi - pi orbital interaction. Fluorescence of these excimers are red shifted and results in structureless broad emission band. Pyrene is well-suited for studies on biophysical phenomena like lateral diffusion, inter or trans-bilayer movement of lipid and lateral organization of membranes. Microcrystals of aromatic compounds, such as perylene, coronene, anthracene and pyrene suspended in aqueous solutions, have been found to exhibit anomalous fluorescence spectra different from those of bulk. Our group has previously reported that the fluorescence spectra of single microcrystals are distinctly different from those of excimer emission but are similar to those of the crystalline thin film. In this work, we have used surfactant assisted self-assembly method to recrystallize nano-micro crystals of pyrene. We have undertaken this study in view of the recent investigation that reports excimer formation in nanocrystals. It has been found that while within the absorption band corresponding to the monomer, the excimer emission is dominant, higher aggregates continue to contribute due to excitation into the absorption tail of the nano-micro crystalline pyrene. By doping the synthesized microcrystals on polymer microcavities, whispering gallery modes (WGMs) were observed. WGMs find potential applications in sensing of several physical quantities like size, refractive index, pressure, temperature.

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