Luogen Deng

Ray-trace simulation of CuInS(Se)(2) quantum dot based luminescent solar concentrators

To enhance the performance of luminescent solar concentrator (LSC), there is an increased need to search novel emissive materials with broad absorption and large Stokes shifts. I-III-VI colloidal CuInS2 and CuInSe2 based nanocrystals, which exhibit strong photoluminescence emissions in the visible to near infrared region with large Stokes shifts, are expected to improve performance in luminescent solar concentrator applications. In this work, the performance of CuInS(Se)2 quantum dots in simple planar LSC is evaluated by applying Monte-Carlo ray-trace simulation. A systematic parameters study was conducted to optimize the performance. An optimized photon concentration ratio of 0.34 for CuInS2 nanocrystals and 1.25 for CuInSe2 nanocrystals doping LSC are obtained from the simulation. The results demonstrated that CuInSe2 based nanocrystals are particularly interesting for luminescent solar concentrator applications, especially to combine with low price Si solar cells.

Colloidal Synthesis of CH3NH3PbBr3 Nanoplatelets with Polarized Emission through Self‐Organization

We report a combined experimental and theoretical study of the synthesis of CH3 NH3 PbBr3 nanoplatelets through self-organization. Shape transformation from spherical nanodots to square or rectangular nanoplatelets can be achieved by keeping the preformed colloidal nanocrystals at a high concentration (3.5 mg mL-1 ) for 3 days, or combining the synthesis of nanodots with self-organization. The average thickness of the resulting CH3 NH3 PbBr3 nanoplatelets is similar to the size of the original nanoparticles, and we also noticed several nanoplatelets with circular or square holes, suggesting that the shape transformation experienced a self-organization process through dipole-dipole interactions along with a realignment of dipolar vectors. Additionally, the CH3 NH3 PbBr3 nanoplatelets exhibit excellent polarized emissions for stretched CH3 NH3 PbBr3 nanoplatelets embedded in a polymer composite film, showing advantageous photoluminescence properties for display backlights.

Low threshold and coherent random lasing from dye-doped cholesteric liquid crystals using oriented cells

We demonstrate the realization of a coherent random laser in a strongly scattering medium, which contained a dispersive solution of Ag nanoparticles and laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) in cholesteric liquid crystals that was injected into an oriented cell. Multiple scattering of Ag nanoparticles and helical domains greatly enhanced by the oriented cell confinement effect was experimentally verified to account for the coherent lasing observed in our oriented system. Based on non-oriented cells and oriented cells, this paper extends the active and scattering media-based random lasers from the incoherent regime to the coherent regime.

Phase Transformations of Copper Sulfide Nanocrystals: Towards Highly Efficient Quantum‐Dot‐Sensitized Solar Cells

Owing to their high electrical conductivity, tunable plasmonic absorption spectra, low cost, and abundance in nature, Cu2-x S nanocrystals are of great interest as functional materials for photovoltaic and photothermal applications. With the aim of developing low-cost high-efficiency quantum-dot-sensitized solar cells, solution-processed Cu2-x S nanocrystal films are synthesized and their phase transformations upon thermal treatment are investigated. A combination of experimental results and theoretical analysis illustrates the thermodynamic evolution of the crystal structures and the composition caused by the thermal-annealing process. The use of Cu2-x S nanocrystal films as counter electrodes in quantum-dot-sensitized solar cells is also explored. The devices have an optimized power-conversion efficiency of 5.81 % for tetragonal Cu2 S nanocrystal films that are derived from annealed Cu1.8 S nanocrystal films.

Electrically controllable plasmonic enhanced coherent random lasing from dye-doped nematic liquid crystals containing Au nanoparticles.

An electrically controllable plasmonic enhanced coherent random lasing from the dye-doped nematic liquid crystal containing Au nanoparticles is demonstrated. To achieve the optimal control of the RL properties, the polarization of the pump light should be parallel to the rubbing direction of the cells. The lasing output intensity is direction-dependent and the substantial output distributes in an angle range of 0°~30° deviating from the direction of the pump stripe. The coherent feedback associated with the coherent random lasing mainly originates from the cooperative effect of the enhanced localized electric field in the vicinity of Au nanoparticles and the multiple scattering caused by the fluctuations of the liquid crystal director and local dielectric tensor.

Electrically controlled plasmonic lasing resonances with silver nanoparticles embedded in amplifying nematic liquid crystals

We demonstrated an electrical control of coherent plasmonic random lasing with very diluted Ag nanoparticles dispersed in a dye-doped nematic liquid crystal (NLC), in which the external electric field dependent emission intensity and frequency-splitting were recorded. A modified rate equation model is proposed to interpret the observed coherent lasing, which is a manifestation of the double enhancements caused by the plasmon–polariton near-fields of Ag particles on the population inversion of laser dye molecules and on the optical energy density of lasing modes. The featured laser quenching as weakening the applied field indicates that the present lasing resonances are very sensitive to the fluctuant dielectric perturbations in the NLC host, and are thus most likely associated with some coupled plasmonic oscillations among the metal nanoparticles.

Bichromatic coherent random lasing from dye-doped polymer stabilized blue phase liquid crystals controlled by pump light polarization*

In this paper, we investigate the bichromatic coherent random lasing actions from the dye-doped polymer stabilized blue phase liquid crystals. Two groups of lasing peaks, of which the full widith at half maximum is about 0.3 nm, are clearly observed. The shorter- and longer-wavelength modes are associated with the excitation of the single laser dye (DCM) monomers and dimers respectively. The experimental results show that the competition between the two groups of the lasing peaks can be controlled by varying the polarization of the pump light. When the polarization of the pump light is rotated from 0° to 90°, the intensity of the shorter-wavelength lasing peak group reduces while the intensity of the longer-wavelength lasing peak group increases. In addition, a red shift of the longer-wavelength modes is also observed and the physical mechanisms behind the red-shift phenomenon are discussed.