Synthesis of Eu2+/Eu3+ Co-Doped Gallium oxide nanocrystals as a full colour converter for white light emitting diodes.

Eu2+ and Eu3+ co-doped Ga2O3 nanocrystals (Ga2O3:Eu NCs) were synthesized in an organic phase at a low reaction temperature of 300 °C. The surface of Ga2O3:Eu NCs was passivated by oleylamine (OAm) and acetylacetone (acac). The coexistence of Eu2+ and Eu3+ as well as passivation by acac and OAm enable Ga2O3 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 7F0 → 5L6 transition at 395 nm, and 7F0 → 5D2 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 Ga2O3 oxygen defects levels. Furthermore, the resultant Ga2O3: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.