Browsing by Author "Piyali Maity"

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Highly Sensitive Broadband Photodetector Based on PbI2-Passivated CdS:Mn Quantum Dots with a Spectrally Flat Response
(American Chemical Society, 2022) Piyali Maity; Satya Veer Singh; Santanu Das; Anup K. Ghosh; Bhola N. Pal
This paper has demonstrated the role of manganese (Mn) doping in cadmium sulfide (CdS) quantum dots (QDs) and their surface passivation for the fabrication of highly sensitive broadband photodetectors. These photodetectors have been fabricated in a p-n heterojunction geometry using the Mn-doped CdS (CdS:Mn) QDs with TiO2 nanoparticles. The thin film of CdS:Mn QDs has been passivated with lead iodide (PbI2) for faster charge transport and broadening of the spectral response of the device. Our detailed X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy indicate a partial PbS formation, which also causes spectral broadening. In addition, this passivation process enables us to enhance the photosensitivity of the device with a spectrally flat response of quantum efficiency throughout the visible range spectrum (350-700 nm). This work also demonstrated that the photosensitivity of the device gradually increases with Mn doping with a faster photoresponse. The highest detectivity of the device was obtained with 4% Mn-doped dots with a value of ∼3.9 × 1012 Jones under -0.5 V external bias with a photoresponse time of 0.2 s, indicating its very high detectivity with a fast response. © 2022 American Chemical Society.
Modulated Antimicrobial Activity and Drug-Protein Interaction Ability of Zinc Oxide and Cadmium Sulfide Nanoparticles: Effect of Doping with Few First-Row Transition Metals
(Springer, 2023) Imocha Rajkumar Singh; Upashna Chettri; Piyali Maity; Anup K. Ghosh; S.R. Joshi; Sivaprasad Mitra
ZnO and CdS nanoparticle (NP) doped with first row transition metal ions showed significant antibacterial activity towards Gram-negative as well as Gram-positive bacteria. While, the antibacterial activity of ZnO NPs was found to be significant in Gram-negative bacteria, the effect was comparatively less pronounced towards Gram-positive bacteria. The activity was found to increase with increasing concentration of the NPs. Doping of ZnO NP with Fe atom resulted in significant reduction in the efficacy its antimicrobial activity. In comparison, CdS quantum dot showed antibacterial activity both in Gram-negative and Gram-positive bacteria. While Co doped CdS particles did not show any modulated antibacterial activity; doping by Fe atom augments it with increasing the dopant concentration. The interaction of anti-diabetic drug chlorpropamide is significantly stronger with bovine serum albumin adsorbed on Fe-doped CdS in comparison with undoped NPs without significant alteration in the protein secondary structure. Present study reveals that the drug binding ability of proteins can be significantly modulated on judicious choice of NP system and also the dopant. The modulation in antimicrobial activity and the drug binding ability of the adsorbed protein was explained on the basis of structural parameters and different physicochemical properties of the doped NP systems. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Physical properties of Fe-doped CdS quantum dots: single dot rectifying diode application
(Royal Society of Chemistry, 2025) Piyali Maity; Ravi Ranjan Shenthil Kumar; Shambunath Jha; Dibyendyu D. Bhattacharyya; Sandip Chatterjee; Bhola Nath Pal; Anup Kumar Ghosh
The domain of single-molecule based electronic devices has grown remarkably over the past decade by utilizing nanotechnology to improve the efficiency of device fabrication. However, most of the single-molecule devices are based on organic materials. Compared with organic molecules, quantum dots (QDs) are excellent owing to their crystalline nature, environmental stability, narrow emission band and quantum yield with tunable electronic and optoelectronic properties. Here, CdS:Fe QDs were synthesized and analyzed to assess their structural, optical, and electronic properties, and subsequently, they were implemented in fabricating single-dot rectifying diodes. EXAFS revealed the average coordination number of the doped Fe element. The ITO/TiO2/CdS:Fe quantum dot heterostructure rectifying diodes were grown by spin coating and were characterized using scanning tunneling microscopy (STM) at room temperature. STM images revealed the distribution of QDs over the substrate, and the spectra revealed the improved rectification behavior with tunneling up to ∼1000×, revealing their excellent diode functionality. Threshold voltage tuning from 1.62 eV to 0.83 eV indicated the application of these diodes for tunable electronics with low power consumption. Thus, these results indicate the promising use of CdS:Fe QDs for optimized ambient atmosphere rectifying diode applications, opening the way for innovative electronic devices with improved performance and functionality. © 2025 RSC.
Role of Cobalt Doping in CdS Quantum Dots for Potential Application in Thin Film Optoelectronic Devices
(American Chemical Society, 2021) Piyali Maity; Shiv Kumar; Ravi Kumar; S.N. Jha; D. Bhattacharyya; S.R. Barman; Sandip Chatterjee; Bhola N. Pal; Anup K. Ghosh
Colloidal quantum dots (QDs) are promising materials for optoelectronic devices. In this paper, monodispersed and environment stable cobalt (Co)-doped CdS QDs have been synthesized and characterized for potential application in thin film optoelectronic devices. The Rietveld refinement profiles of X-ray diffraction data reveal that both undoped and Co-doped CdS QDs exhibit a zinc blende structure without any impurity phase. X-ray photoemission spectroscopy has been used for electronic structure and valence state analysis. The detailed information about the doping, coordination number, and local geometry has been studied with XANES and EXAFS measurements. Analysis of Raman spectra reveals that the intensity of longitudinal optical (LO) modes varies considerably due to short-range structural disorder. Absorption spectra also show the creation of a new doping band (DB) near the NIR region in Co-doped CdS QDs which is not observed for doping of many other transition metals. The width of this DB increases with an increase in the doping concentration, and enhancement of photoconductivity of the thin film heterojunction of the samples has been obtained. Evolution of the new DB and enhancement of the photocurrent upon Co doping make the prepared quantum dots very promising materials to exploit for fabricating UV−vis/NIR thin film optoelectronic devices.(Figure presented) © 2021 American Chemical Society.
Selective near-infrared (NIR) photodetectors fabricated with colloidal CdS:Co quantum dots
(Royal Society of Chemistry, 2019) Piyali Maity; Satya Veer Singh; Sajal Biring; Bhola N. Pal; Anup K. Ghosh
Herein, cobalt-doped cadmium sulphide CdS (CdS:Co) quantum dots (QDs) were synthesized by an organometallic synthesis route using different doping concentrations of Co ranging from 1 to 8%. Optical absorption data indicate the appearance of a new NIR absorption peak of the QDs due to Co doping; moreover, the intensity of the peak increases with the doping concentration; this NIR absorption peak originates from the existence of a doping band located in close vicinity to the valence band inside the band gap. The electrical conductivities of the CdS:Co thin films 'in the dark' show increasing conductivity with doping concentration; this supports the enhancement of the carrier concentration in the valence/conduction band. In addition to the dark current, the photosensitivities of these CdS:Co QDs thin film increase gradually with doping, and significant enhancement was observed in the zinc oxide (ZnO) CdS:Co QD heterojunction structure. Lateral ZnO/CdS:Co heterojunction photodetectors with different doping concentrations of Co2+ show selective NIR sensitivity, which is not realized in the case of undoped CdS. The highest detectivity was observed for the 8% doped CdS:Co heterojunction photodetector, with the detectivity of 3.1 × 1011 Jones with illumination of 820 nm wavelength light under 5.0 V external bias, which is significantly high for an NIR photodetector. © 2019 The Royal Society of Chemistry.
Single quantum dot rectifying diode with tunable threshold voltage
(Royal Society of Chemistry, 2017) Gopal S. Kenath; Piyali Maity; Yogesh Kumar; Hemant Kumar; Vinod K. Gangwar; Sandip Chaterjee; Satyabrata Jit; Anup K. Ghosh; Bhola N. Pal
An ambient atmosphere single quantum dot (QDs) rectifying diode with tunable threshold voltage has been fabricated using cobalt (Co) doped CdS QDs with a device structure of ITO/ZnO/QDs. Current-voltage (I-V) characterization of this device has been tested using ambient atmosphere scanning tunnelling microscope (STM). The scanning tunnelling spectra (STS) shows a very high rectification behavior of this single dot based device with a ratio of 103. The threshold voltage of this device decreases with increase in doping concentration of QDs. Reduction of this turn-on voltage occurs due to the formation of additional energy band of Co impurity within the band gap of QDs that exist closer to the valance band (VB) of CdS. Existence of this additional energy band has also been observed in the UV-VIS absorption data of Co doped CdS, which introduces an additional absorption peak in the near infrared region. This impurity band is fully populated at room temperature and the width of this band increases with doping concentration, which is the key for the tunability of threshold voltage. This finding has been explained with one empirical model of relative band shifting of semiconductor-QDs-tip interfaces with positive and negative substrate bias. © 2017 The Royal Society of Chemistry.
Structural, Optical, and Electronic Properties of NixCd1–xS Quantum Dots: Implications for Photodetection Applications
(American Chemical Society, 2025) Nikita Kumari; Sandeep Dahiya; Chetna Gautam; Piyali Maity; Sandip Chatterjee; Bhola Nath Pal; Anup Kumar Ghosh
X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to study the structural and morphological characteristics of pure and Ni-doped CdS (CdS:Nix) (x = 0–6 atomic %) QDs synthesized via the hydrothermal method. Inductively coupled plasma mass spectrometry (ICP-MS) and EDS measurements have been carried out for quantifying the elemental composition. Due to Ni-doping, the short-range structural disorder causes a significant variation in the intensity of the longitudinal optical (LO) modes of Raman spectra. Optical absorption has been broadened with Ni doping, resulting in a reduction of the band gap from 2.42 eV (for CdS) to 2.36 eV (for CdS:Ni6). Photoluminescence (PL) spectra show various peaks associated with surface defects, near band emission (NBE), sulfur vacancies, photoinduced charge carrier separation, and recombination processes. To investigate the chemical states and valence band spectra of Ni-doped CdS QDs, X-ray photoemission spectroscopy (XPS) has been utilized. To realize their applicability in electronic devices, bilayer heterostructure photodetectors (PDs) have been fabricated on the glass substrate by using CdS:Nix QDs and sol–gel-derived SnO2(as a charge transport layer), viz., Glass/SnO2/CdS:Nix QD PDs. The performance of the device has been improved with a Ni-doping concentration in CdS QDs. The optimized device has been achieved with high photocurrent (28.2 mA/cm2), high figure-of-merit performance having a responsivity of 2.23 A/W, and detectivity of 2.1 × 1013Jones at a wavelength of approximately 450 nm under 5 V external bias for CdS:Ni6 QD heterostructure PD. Furthermore, this PD shows good response kinetics and are quite stable over time indicating its operational stability. © 2025 American Chemical Society
Unraveling the physical properties of Mn-doped CdS diluted magnetic semiconductor quantum dots for potential application in quantum spintronics
(Springer, 2022) Piyali Maity; Ravi Kumar; S.N. Jha; D. Bhattacharyya; Ranjan Kumar Singh; Sandip Chatterjee; Anup Kumar Ghosh
The tunability of structural, optical, electronic, and magnetic properties in semiconductor quantum dots (QDs) makes them promising materials for multiple spintronic and optoelectronic applications. However, controlling the size of QDs to tune these properties is challenging due to their quantum size and high sensitivity to the ambient atmosphere. Here, we demonstrate successfully synthesized tunable Mn-doped cadmium sulfide (0% ≤ Mn ≤ 6%) diluted magnetic semiconductor QDs by hot injection chemical route. XRD and TEM studies confirmed that undoped and Mn-doped CdS QDs are polycrystalline in cubic phase without having any dopant-related signature. The XPS study shows the spin–orbit split due to Mn-doping and the atomic percentage of each element present in the prepared sample has been calculated from XPS data. XANES (X-ray Absorption Near Edge Structure) study shows that the Cd has the same oxidation state (+2) in the undoped and Mn-doped CdS QDs and also Mn has +2 oxidation state in Mn-doped CdS QDs. Extended X-ray Absorption Fine Structure (EXAFS) measurements show local structural disorder in higher doping concentration of Mn. It also shows that due to Mn doping, the coordination number of S in all the Mn-doped samples have the S vacancy compared to undoped CdS. No significant change has been observed in FTIR spectra after Mn doping. Raman spectra exhibits two longitudinal optical (LO) modes at 299 cm−1 and 598 cm−1. The intensity of the first LO peak decreases rapidly and linearly due to local structural and short-range disorder induced with increasing Mn concentration in CdS. UV–Vis spectroscopy reveals non-linear variation of bandgap energy showing the downwards bowing with increasing Mn-doping concentration. PL and TRPL indicate appearance of surface defect states with Mn-doping. TRPL spectra show decrease in decay time due to Mn‐doping. Room temperature ferromagnetism of Mn-doped CdS QDs confirms the diluted magnetic semiconductor behavior, which would play key role in quantum spintronics. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.