Optical properties of nanocrystalline Y₂O₃:Eu depending on its odd structure

The structure of nanocrystalline Y₂O₃:Eu prepared by a combustion reaction was analyzed by XRD and high-resolution electron microscopy. Compared with a large-scale particles, 5-nm Y₂O₃:Eu particles presented as distorted crystallite and rough surfaces. Luminescent and absorption properties of nano-Y₂O₃:Eu showed remarkably particle size effects. At Y₂O₃:Eu particle sizes smaller than 10 nm some new results were observed: (a) a red shift of the charge-transfer-state absorption; (b) new emission bands of Eu³⁺ in the ⁵D₀→⁷F₂ region; (c) luminescent decay of energy level ⁵D₀ of Eu³⁺ turning to a two-step exponential; and (d) a pronounced increase in quenching concentration and much lower phonon density compared with those of the bulk material. All these phenomena can be attributed to the effect of the softened lattice and surface state of the nanomaterial. The latter was confirmed by stronger excitation by the host absorption after the surface modification.