Up-conversion luminescence of neodymium oxide nanocrystals-doped TiO2/ormosils composite films and strip waveguides

Abstract

Neodymium oxide nanocrystals are synthesized by an inverse microemulsion method. XRD, XPS and HRTEM are used to characterize the properties of the neodymium oxide nanocrystals. Results show that the prepared neodymium oxide particles have obvious "column” structure with a column width of 400 ~ 600 nm and a length of 1 ~ 4 µm and have nanocrystalline structure with a high crystallinity. Neodymium-doped TiO2/organically modified silanes (ormosils) organic–inorganic composite films were prepared by using a sol–gel spin coating method. Up-conversion emission and optical transmittance of the films baked at different temperature were studied. Results indicate that the up-conversion emission occurs at about seven wavelength numbers of 387, 404, 421, 436, 450, 478 and 487 nm, of which the bright blue emission at 436 nm has the strongest intensity. There is a high optical transmittance value of above 88% for all the samples in the wavelength number 500 ~ 1000 nm. Optical waveguide properties including the optical transmission modes and loss of the composite films were measured. The photochemical properties of the composite films were also demonstrated by FTIR spectra. Besides, an energy level diagram was used to explain the mechanism of the up-conversion emission from neodymium oxide nanocrystals. Finally, strip waveguides with different waveguide sizes were built in the composite films through a UV soft nanoimprint technique and the surface morphology of the waveguides was observed by SEM. The as-prepared neodymium-doped composite films have potential applications in the areas of photonics and micro-optical devices.