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Directionally solidified Al2O3-Yb3Al5O12 eutectics for selective emitters

AuthorsOliete, Patricia B.; Mesa, M. Cristina; Merino, R. I. ; Orera, V. M.
KeywordsDirectionally solidified eutectic ceramics
Optical absorption
Selective emission
Issue Date2016
CitationSolar Energy Materials and Solar Cells 144: 405-410 (2016)
AbstractAl2O3-Yb3Al5O12 eutectic rods were directionally solidified using the laser floating zone method at rates between 25 and 750 mm/h. The microstructure consisted of an interpenetrated network of both eutectic phases for all the growth rates. The size of the phases was strongly dependent on the growth rate, the eutectic interspacing decreasing from 4.5 μm at the lowest growth rate to 600 nm at 750 mm/h. The optical transmission of the sample with coarser microstructure was measured and compared with that of an Yb3Al5O12 single crystal grown >ad hoc> using the same method. The apparent >oscillator strength> of the single 2F7/2→2F5/2 Yb3+ absorption band was larger in the eutectic sample than in the single crystal, which was attributed to the increase in the light path caused by multiple refractions at the eutectic interphases. The thermal emission of the eutectic rod was studied between 1000 °C and 1500 °C. An intense and relatively narrow emission band at about 1 μm corresponding to the 2F5/2→2F7/2 Yb3+ electronic transition was observed in the whole temperature range. The intensity of the band increased with the temperature up to about 1300 °C. At higher temperatures a saturation of the selective emission was observed which was attributed to the competition between the increase in the thermal population of the excited state and the enhancement of the non-radiative de-excitation channels with the temperature.
Identifiersdoi: 10.1016/j.solmat.2015.09.053
issn: 0927-0248
e-issn: 1879-3398
Appears in Collections:(ICMA) Artículos
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