Europium-doped La2O3 nanocrystalline powders with sizes in the range of 50-200 nm have been obtained by the modified sol-gel Pechini method. These nanocrystals have been deagglomerated using sonication for 3 h and have been dispersed into a semiconductor P3HT polymeric matrix. We studied and analysed the spectroscopic properties of the trivalent europium in the hexagonal La2O3 nanocrystals dispersed in the polymer. The luminescence spectrum of Eu3+ in these nanocrystals is dominated by the 5D0 → 7F2 transition with a maximum intensity peak located at 626 nm. We observed that P3HT absorbs part of the light emitted by the nanoparticles. These properties look promising for using this material as a down-converter material in solar cells.