Abstract
Ultraviolet upconversion emissions of 246.2 and from levels of ions were observed in : 10% , 0.7% nanocrystals under excitation from a laser diode. The levels of ions can be efficiently populated by energy transfer processes of and . A six-photon upconversion process was confirmed by the dependence of emission intensity on the pumping power. The upconversion mechanism in the six-photon process was discussed based on excited state absorption of ions, cross relaxation energy transfer between two excited ions, and energy transfer between and or ions.
© 2008 Optical Society of America
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