List of Publications
Google Scholar: Link
Riyanka Karmakar et al., “Ultrafast Carrier Dynamics in Strongly and Weakly Coupled Few-layer WS2 and Atomically Precise Ag29 Nanohybrid”, (to be submitted).
Riyanka Karmakar, Dipendranath Mandal, Megha Shrivastava, and K. V. Adarsh, “Defect-mediated carrier dynamics and third-order nonlinear optical response of WS2 quantum dots”, Opt. Lett. 47, 5196-5199 (2022). (Impact factor- 3.56 in 2023), (Citation- 4).
· We observed highly luminescent (⁓30% of total emission) defect states in the lower energy side of the photoluminescence (PL) spectra.
· For 800 nm (120 fs) excitation corresponding to the half of the bandgap open aperture Z-scan at shows two-photon absorption (TPA). The photoexcited carriers generated in this process reach just the exciton line and produce bound carriers. Thereby, the nature of the nonlinear refractive index (n2) shows self-focusing (positive) behavior.
· 532 nm (7 ns) excitation, which has energy close to the band-edge states, shows reverse saturable absorption (RSA) due to the sequential absorption of photons from the shallow defect states. This sequential absorption leads to the generation of a large number of free carriers due to the excitation well above the bandgap, which changes the nature of n2 to self-defocusing (negative).
Pravrati Taank†, Riyanka Karmakar†, Rituraj Sharma, Rajesh Kumar Yadav, Megha Shrivastava, Naresh Chandra Maurya, Tuhin Kumar Maji, Debjani Karmakar, and K. V. Adarsh, “An Insightful Picture of Multi-particle Recombination in Few-layer MoS2 Nanosheets”,
J. Phys. Chem. C, 126, 1, 416-422 (2022). (Impact factor- 4.177 in 2023), (Citation- 12).
†Contributed equally
Pravrati Taank, Riyanka Karmakar, and K. V. Adarsh, “Exciton Recombination in Few-layer MoS2 Nanosheets: Role of Free carriers and Defects”, Surf Interface Anal. 1–5 (2023) (Impact factor- 1.665 in 2019).
The important findings of our manuscript are briefly described in bullets:
-
Using energy and fluence-dependent transient absorption (TA) spectroscopy, we provide a comprehensive understanding of the role of free carriers, excitons, and defects in carrier dynamics.
-
We theoretically investigate various configurations of sulfur-vacancies by density functional theory (DFT) and time-dependent DFT.
-
Multi-particle (excitons and free carriers) generated by excitation well above the electronic bandgap exhibit distinct recombination times, i.e., free carriers slow down the recombination by orders of magnitude relative to excitons. In contrast, excitons generated upon near quasi-particle excitation decay much faster ~ 3 ps due to exciton capture to defects.
-
The numerically simulated rate equation model of TA spectra matches well with the experimental results, further supporting defect-assisted recombination.
Naresh Chandra Maurya, Riyanka Karmakar, Rajesh Kumar Yadav, Pravrati Taank, Santu Kumar Bera, Anirban Mondal, Dipendranath Mandal, Megha Shrivastava, Md. Nur Hasan, Tuhin Kumar Maji, Debjani Karmakar, and K. V. Adarsh, “Exciton many-body interactions and charge transfer in CsPbBr3/graphene derivatives”, Phys. Rev. B 108, 155417 (2023). (Impact factor- 3.908 in 2023)
The important findings of our manuscript are briefly described in bullets:
-
Change in the dielectric environment at the interface results in the significant reduction of the binding energies of exciton and biexciton of CsPbBr3 nanocrystals.
-
Our ultrafast transient absorption measurements reveal that bandgap renormalization and Auger recombination rates are decreased in the presence of GO(RGO) which are the consequences of charge transfer.
-
Ultrafast charge transfer from CsPbBr3 nanocrystals to GO(RGO) occurs in 7.0 ± 0.4(4.2 ± 0.1) ps, which is one order of magnitude faster than other acceptor materials such as 1-Aminopyrene, phenothiazine, metal oxide, fullerene, and anthraquinone. These results indicate that GO(RGO) can serve as an excellent acceptor and can be utilized as a transparent conducting layer material.
1) Riyanka Karmakar, Dipendranath Mandal, and K. V. Adarsh, “Third-Order Nonlinear Optical Response and Optical Limiting of WS2 Quantum Dots”, Advanced Photonics Congress 2022, Technical Digest Series (Optica Publishing Group, 2022), paper NpTh2F.2. https://doi.org/10.1364/NP.2022.NpTh2F.2
2) Riyanka Karmakar, Dipankar Sen, Dipendranath Mandal, and K. V. Adarsh, “Ultrafast Charge-Transfer Mediated Indirect-Excitons in CsPbBr3/MoS2 Heterostructure”, Conference on Lasers and Electro-Optics (CLEO-2021), San Jose, California, USA, JW1A. 100.
https://doi.org/10.1364/CLEO_AT.2021.JW1A.100
3) Riyanka Karmakar, Pravrati Taank, and K. V. Adarsh, “Trapped Carrier Hopping and Unusual Bottleneck in Coalescence Dynamics of MoS2 Few Layers”, AIP Conference Proceedings 2369 (2021), 020110. https://doi.org/10.1063/5.0060838
4) Riyanka Karmakar, and K. V. Adarsh, “Unravelling the role of trap states on carrier dynamics of WS2 quantum dots”, Conference on Lasers and Electro-Optics (CLEO-2020), San Jose, California, USA_SW3G.6. https://doi.org/10.1364/CLEO_SI.2020.SW3G.6. (Citation- 1).
2) Riyanka Karmakar, and K. V. Adarsh, “Pulse-width dependent sign-reversal of third-order nonlinear refractive index in WS2 quantum dots”, Bulletin of the American Physical Society_2021. APS March Meeting, Abstract ID L59.00010.