- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Phonon-Driven Energy Relaxation in PbS/CdS and PbSe/CdSe Core/Shell Quantum Dots
摘要： We study the impact of the chemical composition on phonon-mediated exciton relaxation in the core/shell quantum dots (QDs), with 1-nm core made of PbX and the monolayer shell made of CdX, where X=S and Se. For this, time-domain non-adiabatic dynamics (NAMD) based on Density Functional Theory (DFT) and Surface Hopping techniques are applied. Simulations reveal twice faster energy relaxation in PbS/CdS than PbSe/CdSe due to dominant couplings to higher-energy optical phonons in structures with sulfur anions. For both QDs, the long-living intermediate states associated with the core-shell interface govern the dynamics. Therefore, a simple exponential model is not appropriate, and the four-state irreversible kinetic model is suggested instead, predicting 0.9 ps and 0.5 ps relaxation rates in PbSe/CdSe and PbS/CdS QDs, respectively. Thus, 2-nm PdSe/CdSe QDs with a single monolayer shell exhibit the phonon-mediated relaxation time sufficient for carrier multiplications to outpace energy dissipation and benefit the solar conversion efficiency.
关键词： Density Functional Theory,phonon-driven energy relaxation,PbSe/CdSe,PbS/CdS,core/shell quantum dots,Surface Hopping techniques,non-adiabatic dynamics
更新于2025-09-23 15:21:01
-
PbS and PbS/CdS quantum dots: Synthesized by photochemical approach, structural, linear and nonlinear response properties, and optical limiting
摘要： In this work, PbS and PbS/CdS core–shell quantum dots (QDs) were synthesized by a new photochemical approach. Prepared QDs were characterized by means of x-ray diffraction (XRD), ?eld emission scanning electron microscopy (FESEM), energy dispersive x-ray analysis (EDAX), UV–Vis, and Z-scan analyses. Synthesized QDs were in a cubic phase with a spherical morphology, and the crystallite sizes are estimated using the strain–size method. A uniform shift of Bragg diffraction peaks and quenching (200) Bragg plane are interpreted as the growth of the CdS shell. Linear optical properties were investigated using Urbach analysis and Tauc formula. It was found that the density of states of QD conduction and valence bands are three dimensional. The estimated sizes of PbS QDs and PbS/CdS using exciton absorption peaks at room temperature are 1.8 and 2.7 nm, respectively, which are in good agreement with the strain–size plot analysis. The growth of the CdS shell resulted in a considerable decrease in the nonlinearity refractive index and a signi?cant increase in the nonlinear absorption.
关键词： PbS/CdS,photochemical synthesis,PbS,optical limiting,quantum dots,nonlinear optical properties
更新于2025-09-19 17:13:59
-
Characterization of PbS films deposited by successive ionic layer adsorption and reaction (SILAR) for CdS/PbS solar cells application
摘要： The properties of PbS thin films deposited by Successive Ionic Layer Adsorption and Reaction (SILAR) method were analyzed and applied in PbS/CdS heterojuction solar cells. In this study for n-type layer, cadmium sulfide thin films were deposited on transparent conductive oxide (ITO) substrates by Chemical Bath Deposition (CBD) technique followed by deposition of PbS film using different deposition cycles, 15, 20, 30, 40 and 60 to obtain different thicknesses from 90 nm to 658 nm. Morphological, structural and optical properties were investigated. The roughness of the PbS films were found to be in the range of 10–162 nm, depending on the number of cycles. The films of PbS present a band gap value of 0.6 eV. PbS/CdS heterojunctions were studied as solar cells, it was observed that 40 cycles PbS film has a greater photovoltaic conversion efficiency.
关键词： SILAR,PbS films,solar cells,PbS/CdS heterojuctions
更新于2025-09-19 17:13:59
-
Intrinsic exciton photophysics of PbS quantum dots revealed by low-temperature single nanocrystal spectroscopy
摘要： With a tunable size-dependent photoluminescence (PL) over a wide infrared wavelength range, lead chalcogenide quantum dots (QDs) have attracted significant scientific and technological interest. Nevertheless, the investigation of intrinsic exciton photophysics at the single-QD level has remained a challenge. Herein, we present a comprehensive study of PL properties for individual core/shell PbS/CdS QDs emissive near 1.0 eV. In contrast to the sub-meV spectral linewidths observed for II/VI QDs, PbS/CdS QDs are predicted to possess broad homogeneous linewidths. Performing spectroscopy at cryogenic (4 K) temperatures, we provide direct evidence confirming theoretical predictions, showing that intrinsic linewidths for PbS/CdS QDs are in the range of 8-25 meV, with an average of 16.4 meV. In addition, low-temperature, single-QD spectroscopy reveals a broad low-energy side emission attributable to optical as well as localized acoustic phonon-assisted transitions. By tracking single QDs from 4 K to 250 K we were able to probe temperature-dependent evolutions of emission energy, linewidth and line shape. Finally, polarization-resolved PL imaging showed that PbS/CdS QDs are characterized by a 3D emission dipole, in contrast with the 2D dipole observed for CdSe QDs.
关键词： PbS/CdS,bandgap,spectral linewidth,infrared nanocrystals,polarization,single nanocrystal spectroscopy
更新于2025-09-12 10:27:22