Erbium-doped ZrO 2 nanoparticles are prepared by a sol-emulsion-gel technique. The effects of the Er 3+ concentration and different codopants (Yb 3+ and Y 3+ ) in the ZrO 2 matrix on the upconverted emission are reported. Green and red upconversion emission at 550 and 670 nm were observed from these oxide nanocrystals with 980 nm excitation. The overall intensity decreases with an increasing concentration of erbium in zirconia. The presence of codopants (Y 3+ and Yb 3+ ) also increases the overall intensity of the upconverted emission. The emission spectra and the pump intensity dependence of the luminescence intensities are used to understand the excitation mechanism. These results confirm that upconverted emission in these materials is due to a two-photon excited-state absorption (ESA)/energy transfer upconversion (ETU) process.

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The effects of the erbium concentration, crystal size, crystal phase, and different processing temperatures on the upconverted emission of Er3+ in BaTiO3 and TiO2 nanocrystals are reported. A cw diode laser at 975 nm was used as a pump source for resonant sequential excitation of the 4I11/2 and 4F7/2 levels. Green and red upconversion emission at 550 and 670 nm were observed from these oxide nanocrystals with 975 nm excitation. With the same Er3+ concentration, the upconversion emission intensity from BaTiO3 was higher than that observed in the TiO2 host. In the TiO2 matrix, the maximum upconversion emission intensity of Er3+ was found for samples calcined at 800 °C where both the anatase and the rutile phases were present. The observed emission characteristics and the pump intensity dependence of the luminescence intensity confirm that the upconverted emission in these materials is produced by two-photon excited-state absorption (ESA) processes.

The effects of crystal size and crystal phase on the upconverted emission of Er3+ in ZrO2 oxide nanocrystals are reported. Green (550 nm) and red (670 nm) upconversion emission were observed at room temperature from the S43/2 and F49/2 levels of Er3+:ZrO2 nanocrystals. It is found that at 850 mW of cw excitation power, the total luminescence was 11960 Cd/m2 for 1000 °C heated sample. We observed that the overall upconversion luminescence intensity depends on crystal structure and particle size. We have also confirmed that upconversion process in all these samples results from a two-photon excited-state absorption process.

High-order harmonic generation at 4MHz as a light source for time-of-flight photoemission spectroscopy