Observation of exceptional strong emission transitions 5Dj (j=1−3) to 7Fj (j=1−3): Multicolor from single Eu3+ ion doped La2O3 nanoparticles

Eu3+ ion doped La2O2CO3 and La2O3 nanoparticles have been synthesized through hydrothermal route with subsequent heat-treatment. It is found that La2O2CO3 phase is highly stable at ambient atmosphere and decomposes to La2O3 at or above 700 °C. Exceptional stronger emissions from 5Dj (j=1−3) to 7Fj (j=1−3) transitions are observed compared to most probable 5D0 to 7Fj (j=1−3) transitions in 1 and 3 at% Eu3+ doped samples heated at 900 °C under 278 nm excitation. This may be ascribed due to minimum cross-relaxation among 5Dj (j=1−3) levels. Significant decrease of emission intensity from 5D1 or 5D2 level and subsequent increase of emission intensity from 5D0 level on increasing Eu3+concentration up to 10 at% indicate relaxation of excited electrons from 5Dj=1, 2 to 5D0 level. Excitation at 394 nm shows strong background emission intensity in 425–600 nm due to different defect states/intermediate bands present within host electronic band. Colors including blue, green, yellow, pink and red to white could be produced by changing concentration of Eu3+, excitation wavelength and annealing temperature. Samples are dispersible and could be incorporated in polyvinyl alcohol (PVA) films. Materials will also be potential candidates for light emitting diodes (LEDs) and bio-labeling.