Eu^(3+):Y_2O_3纳米微粒的尺寸效应和表面态效应的研究

Size Confinement and Surface State Effect of Eu^(3+): Y_2O_3 Nanocrystals

通过相同掺杂浓度但不同颗粒尺寸的Ｅｕ：Ｙ２Ｏ３纳米晶，和相同颗粒尺寸但掺杂浓度不同的纳米晶的发 光衰减曲线研究了表面态和限域作用对能量传递的影响。纳米晶与体材料相比，有更高的猝灭浓度，分析了纳 米材料中发光中心的猝灭浓度提高的原因。由于纳米材料与体材料相比，纳米晶中的缺陷密度很小，纳米晶中 有较少的体猝灭中心。选择合适的颗粒尺寸并对其进行表面修饰，将获得较高发光效率和较高的猝灭浓度。

The luminescence decay curves of Eu3+: Y2O3 nanocrystals with different diameters and same doped concentration were studied. The surface states act as quenching centers in the luminescence, so the measured lifetimes decrease along with the decreases of the particle size. And the luminescence decay curves of nanocrystals with the same diameter and different doped concentrations were also studied. The measured lifetimes decrease with the increasing of the doped concentration. In high dopant concentration, energy transfer between luminescent ions is caused by exchange interaction. The energy transfer between dopant ions accelerates the quenching through the surface states. The surface state and size confinement bring the different influences to energy transfer in nanocrystals with different size nanocrystals. It is obtained that nanocrystals have much higher quenching concentration than that of bulk material and the quenching concentration of 40um nanoparticles is higher than that of 5nm nanopaticles. The reason of the increasing of quenching concentration is analyzed. Impurity and dislocation may act as bulk quenching center. If the same raw materials were used in preparing samples, concentrations of impurity are identical despite the sizes of the nanocrystals. But the configuration of dislocation is influenced by the nanocrystals size. Dislocation in nanocrystals is not stable below a certain critical size. Nanocrystal has hardly any dislocation when its size is smaller than the critical size. Dislocation density of nanocrystals would be much lower than that of bulk material. The number of bulk quenching center is very small. It has been found that nanocrystals have higher quenching concentration than bulk material. However, experimental evidence indicates that the relationship between quenching concentration and the particle size is not a monotonic function. This is because that surface state effect and size confinement effect bring opposite influences to the energy transfers in nanocrystals. So if a appropriate size of nanocrystals is selected and the surface of nanocrystals are decorated, the nanocrystals doped luminescence material, which has high photoluminescence efficiency and high quenching concentration should be produced.