Synthesis of Eu/Eu Co-Doped Gallium oxide nanocrystals as a full colour converter for white light emitting diodes.

Eu and Eu co-doped GaO nanocrystals (GaO:Eu NCs) were synthesized in an organic phase at a low reaction temperature of 300 °C. The surface of GaO:Eu NCs was passivated by oleylamine (OAm) and acetylacetone (acac). The coexistence of Eu and Eu as well as passivation by acac and OAm enable GaO to be excited in the broad spectral range of 200-500 nm. The broadened absorption band is attributed to the strong acac → Ln(III) ligand to the metal charge transfer transition at ∼370 nm, Eu(III) f-f allowed F → L transition at 395 nm, and F → D transition at 465 nm, as well as the efficient electronic transition of Eu(II) 4f → 5d at ∼400 nm. Under near-ultraviolet excitation, white light emission can be achieved by combining orange-red light from f-f electronic transition of Eu(III) with blue-green-yellow light from GaO oxygen defects levels. Furthermore, the resultant GaO:Eu NCs with optimized quantum yield of 14.5% were coated onto 395 nm near-ultraviolet chips to fabricate a white light emitting diode. It exhibits a luminous efficiency of 34 lm/W, CIE colour coordinate of (0.2964, 0.2831) and high colour rendering index of 80.