Manoj K. Sharma

Near‐Unity Emitting Copper‐Doped Colloidal Semiconductor Quantum Wells for Luminescent Solar Concentrators

Doping of bulk semiconductors has revealed widespread success in optoelectronic applications. In the past few decades, substantial effort has been engaged for doping at the nanoscale. Recently, doped colloidal quantum dots (CQDs) have been demonstrated to be promising materials for luminescent solar concentrators (LSCs) as they can be engineered for providing highly tunable and Stokes-shifted emission in the solar spectrum. However, existing doped CQDs that are aimed for full solar spectrum LSCs suffer from moderately low quantum efficiency, intrinsically small absorption cross-section, and gradually increasing absorption profiles coinciding with the emission spectrum, which together fundamentally limit their effective usage. Here, the authors show the first account of copper doping into atomically flat colloidal quantum wells (CQWs). In addition to Stokes-shifted and tunable dopant-induced photoluminescence emission, the copper doping into CQWs enables near-unity quantum efficiencies (up to ≈97%), accompanied by substantially high absorption cross-section and inherently step-like absorption profile, compared to those of the doped CQDs. Based on these exceptional properties, the authors have demonstrated by both experimental analysis and numerical modeling that these newly synthesized doped CQWs are excellent candidates for LSCs. These findings may open new directions for deployment of doped CQWs in LSCs for advanced solar light harvesting technologies.

Possible decay mechanisms of 220Ra* formed in carbon induced reaction

Using the dynamical cluster decay model (DCM), the decay of 220Ra* compound nucleus formed in 13C+207Pb reaction is studied at various compound nucleus (ECN) energies. The cross sections are calculated for various decay processes like neutron (n)-decay, evaporation residue (ER), fission and αxn channel, which find nice comparison with experimental data. The cross sections are calculated considering quadrupole (β2) deformations with optimum orientation (θiopt) by fitting the necklength (ΔR) parameter. The neck length parameter gives the measure of time scales of the respective decay channels. The potential energy surfaces corresponding to various decay channels are investigated over a wide range of incident energies above the Coulomb barrier. Finally, the competing incomplete fusion (ICF) contribution is analysed for the above mentioned reaction channel.

Cd-free Cu-doped ZnInS/ZnS Core/Shell Nanocrystals: Controlled Synthesis And Photophysical Properties

Here, we report efficient composition-tunable Cu-doped ZnInS/ZnS (core and core/shell) colloidal nanocrystals (CNCs) synthesized by using a colloidal non-injection method. The initial precursors for the synthesis were used in oleate form rather than in powder form, resulting in a nearly defect-free photoluminescence (PL) emission. The change in Zn/In ratio tunes the percentage incorporation of Cu in CNCs. These highly monodisperse Cu-doped ZnInS CNCs having variable Zn/In ratios possess peak emission wavelength tunable from 550 to 650xa0nm in the visible spectrum. The quantum yield (QY) of these synthesized Cd-free CNCs increases from 6.0 to 65.0% after coating with a ZnS shell. The CNCs possessing emission from a mixed contribution of deep trap and dopant states to only dominant dopant-related Stokes-shifted emission are realized by a careful control of stoichiometric ratio of different reactant precursors during synthesis. The origin of this shift in emission was understood by using steady state and time-resolved fluorescence (TRF) spectroscopy studies. As a proof-of-concept demonstration, these blue excitable Cu-doped ZnInS/ZnS CNCs have been integrated with commercial blue LEDs to generate white-light emission (WLE). The suitable combination of these highly efficient doped CNCs results led to a Commission Internationale de l’Enclairage (CIE) color coordinates of (0.33, 0.31) at a color coordinate temperature (CCT) of 3694xa0K, with a luminous efficacy of optical radiation (LER) of 170xa0lm/Wopt and a color rendering index (CRI) of 88.

sp-d Exchange Interactions in Wave Function Engineered Colloidal CdSe/Mn:CdS Hetero-Nanoplatelets

In two-dimensional (2D) colloidal semiconductor nanoplatelets, which are atomically flat nanocrystals, the precise control of thickness and composition on the atomic scale allows for the synthesis of heterostructures with well-defined electron and hole wave function distributions. Introducing transition metal dopants with a monolayer precision enables tailored magnetic exchange interactions between dopants and band states. Here, we use the absorption based technique of magnetic circular dichroism (MCD) to directly prove the exchange coupling of magnetic dopants with the band charge carriers in hetero-nanoplatelets with CdSe core and manganese-doped CdS shell (CdSe/Mn:CdS). We show that the strength of both the electron as well as the hole exchange interactions with the dopants can be tuned by varying the nanoplatelets architecture with monolayer accuracy. As MCD is highly sensitive for excitonic resonances, excited level spectroscopy allows us to resolve and identify, in combination with wave function calculations, several excited state transitions including spin-orbit split-off excitonic contributions. Thus, our study not only demonstrates the possibility to expand the extraordinary physical properties of colloidal nanoplatelets toward magneto-optical functionality by transition metal doping but also provides an insight into the excited state electronic structure in this novel two-dimensional material.

Decay analysis of 216Th* nucleus using dynamical cluster-decay model

The study of different decay mechanisms of a composite system (equilibrated or non-equilibrated) formed in heavy ion reactions has proven to be useful to extract valuable information regarding nuclear reaction dynamics and associated structure effects. In view of this, the present work aims to study the different fission mechanisms emerging via compound nucleus (CN) and non-compound nucleus (nCN) processes. The decay paths of 216Th∗ nucleus formed in 32S+184W reaction are analyzed at centre-of-mass energy Ec.m. = 123.1u2005MeV. The calculations are performed within collective clusterization approach of dynamical cluster-decay model (DCM). As per the experimental observations of Zhang et al. [PRC 81, 034611 (2010)], the fission decay mechanisms via nCN processes i.e. quasi fission and fast fission also contribute towards the total capture cross-sections. Here, the excitation functions of fusion-fission (σf f), quasi fission (σQ F) and fast fission (σF F) are estimated and compared with available experimental data. Furthermore, the role of angular momentum on various observables of DCM such as fragmentation potential V (MeV), preformation probability P0 and barrier penetrability P, is duly addressed in order to extract relevant inferences associated with the reaction mechanism.The study of different decay mechanisms of a composite system (equilibrated or non-equilibrated) formed in heavy ion reactions has proven to be useful to extract valuable information regarding nuclear reaction dynamics and associated structure effects. In view of this, the present work aims to study the different fission mechanisms emerging via compound nucleus (CN) and non-compound nucleus (nCN) processes. The decay paths of 216Th∗ nucleus formed in 32S+184W reaction are analyzed at centre-of-mass energy Ec.m. = 123.1u2005MeV. The calculations are performed within collective clusterization approach of dynamical cluster-decay model (DCM). As per the experimental observations of Zhang et al. [PRC 81, 034611 (2010)], the fission decay mechanisms via nCN processes i.e. quasi fission and fast fission also contribute towards the total capture cross-sections. Here, the excitation functions of fusion-fission (σf f), quasi fission (σQ F) and fast fission (σF F) are estimated and compared with available experimental d...

Anomalous spectral characteristics of ultrathin sub-nm colloidal CdSe nanoplatelets

We demonstrate high quantum yield broad photoluminescence emission of ultrathin sub-nanometer CdSe nanoplatelets (two-monolayer). They also exhibit polarization-characterized lateral size dependent anomalous heavy hole and light/split-off hole absorption intensities.

2n-emission from 205Pb* nucleus using clusterization approach at Ebeam∼14-20 MeV

The dynamics involved in n-induced reaction with 204Pb target is analyzed and the decay of the composite system 205Pb* is governed within the collective clusterization approach of the Dynamical Cluster-decay Model (DCM). The experimental data for 2n-evaporation channel is available for neutron energy range of 14-20u2005MeV and is addressed by optimizing the only parameter of the model, the neck-length parameter (ΔR). The calculations are done by taking the quadrupole (β2) deformations of the decaying fragments and the calculated 2n-emission cross-sections find nice agreement with available data. An effort is made to study the role of level density parameter in the decay of hot-rotating nucleus, and the mass dependence in level density parameter is exercised for the first time in DCM based calculations. It is to be noted that the effect of deformation, temperature and angular momentum etc. is studied to extract better description of the dynamics involved.