FTIR spectra of samples (a) as-synthesized, (b) heat treated at 900 K for 6 h, and (c) heat treated at 1200 K for 6 h showing the reduction in the fluorescence quenching centers due to heat treatment.
DTA and TGA curves of the doped phosphor.
XRD patterns of doped nanocrystals: (a) as-synthesized, (b) heat treated at 900 K for 6 h, and (c) heat treated at 1200 K for 6 h.
Transmission electron micrograph along with the selected area electron diffraction pattern of the doped phosphor sample annealed at 1200 K for 6 h.
UC emission bands in the 300–500 nm region at a pump power of 50 mW for the as-synthesized phosphor material.
Power dependence of the bands at 383, 411, 458, 491, and 672 nm wavelengths in the phosphor.
Schematic energy level diagram of and possible UC and downconversion transitions and mechanisms involved in their appearance.
Emission from the doped phosphor at a pump power of 600 mW showing a sharp decrease in the intensity of the bands at 383, 411, and 472 nm and an increase in the intensity of the bands at 458 and 491 nm.
(a) Change in intensities of the bands with pump power and (b) graph showing the variation in the intensity of the band at 411 nm with increasing and decreasing pump powers.
Partial energy level diagram of showing the mechanism of phonon absorption and emission at a high pump power.
Continuum emission band in the 300–900 nm region on excitation with 532 nm at a 1.5 W pump power. The 490–580 nm region in the graph has been blocked by the filters in order to avoid a 532 nm excitation.
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