Luminescence, energy transfer, and upconversion mechanisms of nanophosphors (Y(2)O(3) : Eu(3+), Tb(3+), Y(2)O(3) : Tm(3+), Y(2)O(3) : Er(3+), Yb(3+)) both in particle and colloidal forms were studied. The structure, phase, and morphology of the nanopowders and nanocolloidal media were determined by high-resolution TEM and X-ray diffraction. It was shown that the obtained nanoparticles have a round-spherical shape with average size in the range of 4 to 20 nm. Energy transfer was observed for Y(2)O(3) : Eu(3+), Tb(3+) colloidal and powders, upconversion transitions were observed for both Y(2)O(3) : Er(3+) and Y(2)O(3) : Er(3+), Yb(3+) nanophosphors. The dependence of photoluminescence (PL) spectra and decay times on doping concentration has been investigated. The infrared to visible conversion of emission in Y(2)O(3) : Er(3+), Yb(3+) system was analyzed and discussed aiming to be applied in the photonic technology. Copyright (C) 2007 TranKim Anh et al.