Yellow-to-violet upconversion in neodymium oxide nanocrystal/titania/ormosil composite sol-gel thin films derived at low temperature

Neodymium (III) oxide nanocrystals synthesized by the inverse microemulsion technique were dispersed in sol-gel titania/organically modified silane (o rmosil) composite thin films for photonic applications. X-ray diffraction a nalysis and transmission electron microscopy observation show that the neod ymium oxide nanoparticles have a nanocrystalline structure and that the siz e of the nanoparticles is in the range of 5-60 nm. An intense room-temperat ure yellow-to-violet upconversion emission at 402 nm (D-4(3/2)--> I-4(13/2) ) was measured from the composite thin film heated at 100 degreesC upon exc itation with a yellow light at 587 nm. In addition to this violet emission, ultraviolet emission at 372 nm and blue emission at 468 nm were also obser ved. The lifetime of the violet emission was measured and the mechanism of the upconversion emission is proposed, and they indicate excited-state abso rption originating from the long-lived F-4(3/2) excited state should be res ponsible for the yellow-to-violet upconversion. (C) 2001 American Institute of Physics.