Single-particle/molecule spectroscopy is a technique that focuses on studying individual particle or molecule rather than examining a large ensemble of many particles. This approach eliminates the averaging effects found in ensemble measurements, leading to a clearer understanding of the sample. By using single molecule/particle technique, we understand the deeper insights onto the photophysical properties and their spectral heterogeneity in the sample. In our lab, we have developed a custom-built single molecule/particle spectroscopy setup to study the photophysics of quantum and nanomaterials at the single-particle level. We also utilize fluorescence correlation spectroscopy (FCS), a unique diffusion-based technique to further understand the fluorescence properties of the materials. 

The fluorescence spectroscopic analysis of single particles revealed some exciting phenomena that were previously unknown at the bulk level. The single molecule/particle technique also help in understanding the fluorescence blinking or intermittency, which plays an important role in deciding the fate of the fluorescent material for their optoelectronic applications (also shown in above figure). 

Using the combination of ensemble and single particle fluorescence spectroscopy, I was able to unveil the existence of excitation wavelength dependent dark fractions in water dispersible CdTe quantum dots. In another work, i tuned the single quantum dot's fluorescence blinking to utilise them in super resolution micrsocopy (localisation based). 

Notable publications

Nanoscale, 2025, 17, 7, 3919-3929. https://doi.org/10.1039/D4NR04344H

ChemNanoMat. 2022, 8, 10, e202200235. https://doi.org/10.1002/cnma.202200235 

Quantum technologies have the potential to revolutionize various fields, including computing, information processing, sensing, metrology, imaging, cryptography, and communication. These technologies rely on quantum bits, or qubits, which are the quantum analogues of classical bits. Qubits can be implemented using different two-level physical systems, such as superconducting qubits, trapped ion qubits, and photonic qubits. Superconducting qubits use superconducting circuits, trapped ion qubits use atoms or ions, and photonic qubits utilize photons with different colors, phases, or polarizations of photons for qubit generation. Photonic qubits offer several advantages over other types. They can be easily transmitted through optical fibers, are less susceptible to decoherence due to minimal contact with environmental factors, and are a promising candidate for operation at non-zero temperature. In the context of photonic qubits, photons serve as qubits, and single photons are necessary for implementing quantum logic gates and communication protocols.

To realize a photonic qubit, a single photon source is required. A single photon source must generate highly pure single photons on demand with deterministic emission. In our lab, we have utilised colloidal quantum dots to generate single photons with ultra-high purity at room temperature. I was also curious to understand the mechanism of Single Photon Emission from the colloidal quantum dots by utilising various spectroscopic tools at ensemble and single particle level. This detailed understanding can help design and engineer the single photon sources at room temperature.

Notable publication

The Journal of Physical Chemistry Letters, 2025, 16, 23, 5868-5877. https://doi.org/10.1021/acs.jpclett.5c00884