17 May 2016 Measuring the anti-Stokes luminescence of CdSe/ZnS quantum dots for laser cooling applications
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Abstract
The first demonstration of laser cooling of solids was of an ytterbium doped fluorozirconate glass. While this groundbreaking work successfully showed that it is possible to cool solids using laser cooling, rare-earth materials are governed by Boltzmann statistics limiting their cooling ability to about 100 K. Direct-bandgap semiconductors, on the other hand, are governed by Fermi-Dirac statistics, which allows for a theoretical cooling limit of 10 K as well as higher cooling efficiencies. Recently, it was demonstrated that it is possible to cool CdS nanoribbons by 40 K. That success was attributed to CdS strong electron-phonon coupling, which makes it possible to resonantly annihilate more than one longitudinal optical phonon during each up conversion cycle. To further increase the cooling power, large external quantum efficiency is required. A nanostructure is preferred because it creates confined excitons of tunable wavelength and reduces the self-absorption of the anti-Stokes fluorescence owing to the shorter path length for photons to escape the crystal. However, organically passivated quantum dots have a low quantum yield due to surface related trap states. A core-shell nanostructure alleviates this problem by passivating the surface trap states and protecting against environmental changes and photo-oxidative degradation. As such, we chose to investigate CdSe/ZnS core shell structure for laser cooling applications. This article highlights the measurement of the anti-Stokes luminescence, the dependence of the laser wavelength on the anti-Stokes emission of colloidal quantum dots, and the successful incorporation of CdSe/ZnS into polymers.
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Ross S. Fontenot, Ross S. Fontenot, Veerendra K. Mathur, Veerendra K. Mathur, John H. Barkyoumb, John H. Barkyoumb, Carl E. Mungan, Carl E. Mungan, Thanh N. Tran, Thanh N. Tran, } "Measuring the anti-Stokes luminescence of CdSe/ZnS quantum dots for laser cooling applications", Proc. SPIE 9821, Tri-Technology Device Refrigeration (TTDR), 982103 (17 May 2016); doi: 10.1117/12.2222826; https://doi.org/10.1117/12.2222826
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