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Absorption spectrum of , in the region of the transition, showing increased attenuation on the Yb resonance. The solid curve is a Gaussian best fit. Inset: Logarithm of transmission vs thickness measured through a lightly pressed free-standing powder layer.
Luminescence spectra of nanopowder at two incident intensities: Low power (, solid) and high power (, dashed). Excitation wavelength was .
Luminescence intensity measured at vs input power, together with the predicted emission intensity (dashed curve). A quadratic increase in upconversion intensity is evident below , followed by spectral quenching in the region between , and continuum generation above .
Black-body emission intensity vs pump power ( spot diameter ). In the main plot, the lower (upper) branch of the hysteresis loop corresponds to increasing (decreasing) power. Left inset: White-light emission spectrum, corrected for instrumental response. For , photomultiplier sensitivity drops to zero; background is from overlapping spectral orders. The dashed curve is a Planck distribution fit . Right inset: Uncorrected white-light emission spectrum showing large resonant reabsorption features due to ground-state Er ions.
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