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In 1929, German physicist Peter Pringsheim suggested that anti-Stokes emission could lead to bulk matter cooling. One has to irradiate a sample using laser light in the red tail of the absorption spectrum in order to cool a solid. The material that was not cooled will then absorb a photon and absorb additional energy from a phonon, resulting in the creation of a blue-shifted photon of higher energy. Laser cooling also allows for the possibility of portable lasers that need no or smaller external cooling systems because the pump wavelength can be adjusted so that spontaneous anti-Stokes luminescence cooling compensates for the stimulated quantum defect heating. A thermally balanced laser such as this will not suffer from thermal defocusing or heat damage; therefore, such solid-state-lasers would have higher output powers. However, as the temperature rises, the cooling efficiency of rare-earth ions approaches zero. As a result, they have a theoretical cooling limit of 90 K, semiconductors have more effective pump light absorption, lower temperatures of ten K, and the ability to convert the material into electronic and photonic devices as a result. Direct bandgap semiconductors are excellent laser cooling candidate materials, thanks to their flexibility, strong electron-phonon coupling of Group II-VI semiconductors and a solid core-shell quantum dot structure, which minimizes the reabsorption of the anti-Stokes luminescence. We have chosen CdSe/ZnS quantum dots for laser cooling applications due to the likelihood of near-unity quantum efficiencies of CdSe/ZnS.
Source link: https://doi.org/10.1149/ma2017-02/53/2235
Using micro-photoluminescence and micro-Raman spectroscopy, we have investigated two varieties of Zn1-xCdxSe quantum islands in CdSe/ZnSe heterostructure with different size and Cd composition. With increasing thickness of the CdSe layer, the sheet thickness of large Zn1-xCdxSe islands with lower exciton ground state energy will rise, and the large islands' photoluminescence properties of the samples will gradually diminish. The second, the increase of Cd content in the Zn1-xCdxSe quantum islands contributes to the large red shift.
Source link: https://doi.org/10.7498/aps.55.2628
Abstract of this research The CdSe/ZnS quantum dots were synthesized in this report, according to the authors. The photoluminescence stability and the shelf life of the quantum dots increased dramatically when the ZnS shell was grown on the surface shell of CdSe nanoparticles. The absorption and luminescence spectra of absorption and luminescence have been reduced to a shorter wavelength range. The average total hydrodynamic size of the nanoparticles increased after stabilization with a surfactant.
Source link: https://doi.org/10.1088/1757-899x/1008/1/012033
The CdSe/ZnS quantum dots embedded in the chaperonin protein layer deposited on the SiO2 surface were trapped in the CdSe/ZnS quantum dots. As compared to the bare SiO 2 EIS system with a pH response of 35 MV/pH, improvements in pH response with sensitivity of 53. 3 MV/pH have been discovered with CdSe/ZnS Quantum Dots modified EIS system with a pH response of 35 million V/pH, as shown by electrochemical analysis. From the concap V fb results, the CdSe/ZnS updated pH sensor has good stability and repeatability.
Source link: https://doi.org/10.1149/04515.0001ecst
Photons of shorter wavelength than that of the vivid light due to thermal absorption have been obtained by anti-Stokes emission results in photons of shorter wavelength than those of the dramatic light due to thermal absorption. One cannot cool a solid using lasers, so one must irradiate a sample with laser light in the red tail of the absorption spectrum. The material that has been cooled will absorb a photon and absorb additional energy from a phonon to produce a blue-shifted photon of higher energy. Laser cooling can also be adjusted to accommodate portable lasers that need no or lesser external cooling systems, because the pump wavelength can be adjusted such that spontaneous anti-Stokes luminescence cooling compensates for the triggered quantum defect heating. However, as the temperature rises, the cooling efficiency of rare-earth ions approaches zero. Direct bandgap semiconductors are a viable laser cooling candidate material, thanks to this, combined with strong electron-phonon coupling of Group II-VI semiconductors and core-shell quantum dot structure, minimizing the reabsorption of the anti-Stokes luminescence. We have chosen to investigate CdSe/ZnS quantum dots for laser cooling applications due to the possibility of near-unity quantum efficiencies of CdSe/ZnS. The optimum laser excitation wavelength for CdSe/ZnS anti-Stokes emission, according to CdSe/ZnS anti-Stokes emission is 647 nm. This wavelength indicates that the second-harmonic longitudinal optical phonon is closely related to laser photons. We were able to cool a 4-mL colloidal solution containing 2 mg of CdSe/ZnS per 1 mL of toluene at 2. 3°C from room temperature using this wavelength.
Source link: https://doi.org/10.1149/ma2016-02/42/3131
On a Si light absorption layer, CdSe/ZnS quantum dots of various gold nanoparticles sizes were embedded on a Si light absorption layer. The sole Au NPs layer contributes to the overall improvement of Si solar cell's efficiency in the visible spectrum due to the light scattering effect of plasmonic resonance. Because of poor intrinsic spectral response in the UV region, such a downshift layer can raise Si solar cells' overall efficiency. In depth, the optical properties of Au NPs and CdSe QDs, as well as the electrical properties of solar cells in combination with Au/QD layers, are investigated in depth. In addition, the effect of Au NPs size on the solar cell results has been investigated. The blueshift of absorbance has been observed on decreasing the diameters of Au NPs, cooperating with QDs, which results in the improvement of the quantum efficiency in the solar spectrum's broadband.
Source link: https://doi.org/10.3390/app12010083
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