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10 March 2015 Characterization of fluoride nanocrystals for optical refrigeration
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Proceedings Volume 9380, Laser Refrigeration of Solids VIII; 93800Q (2015) https://doi.org/10.1117/12.2079856
Event: SPIE OPTO, 2015, San Francisco, California, United States
Abstract
This paper reports on the characterization of nanocrystalline powders of ytterbium doped YLiF4 for applications in optical refrigeration. Here we used powders with nanocrystals of Yb 3+ concentrations of (10, 15, 20) mol % and lengths (70, 66, 96) nm. Our preliminary spectroscopic measurements did not show an enhancement in the absorption at the long-wavelength tail of the spectra of the nanocrystalline powder when compared with bulk Yb:YLiF4, indicating that the increase of the phonon-assisted excitation is not large enough to play a significant role in cooling in the present conditions. One advantage of nanocrystalline powders over bulk crystals is the possibility of enhancing the absorption by the realization of cavity-less pump recycling through photon localization [1]. While photon localization also increases the reabsorption of the fluorescence depending on the quantum efficiency of the material and can mitigate cooling, it allows the use of crystals of low enough concentrations to avoid deleterious effects such as ion-ion energy transfer followed by quenching. The pump intensity enhancement favors upconversion luminescence to visible wavelengths, which can be used for optical refrigeration and extends the scope of the application for the material. We observed both green and blue emission from the samples and investigate the processes which lead to it. We present the experimental investigation of the nanocrystals’ absorption and emission spectra and the first excited state lifetime measurements, which are used to estimate the nanocrystal’s photoluminescence quantum efficiency.
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Elton Soares de Lima Filho, Marta Quintanilla, Fiorenzo Vetrone, Galina Nemova, Venkata Krishaniah Kummara, and Raman Kashyap "Characterization of fluoride nanocrystals for optical refrigeration", Proc. SPIE 9380, Laser Refrigeration of Solids VIII, 93800Q (10 March 2015); https://doi.org/10.1117/12.2079856
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