Y_2O_2S纳米晶中Tb^(3+)发光的浓度猝灭

Concentration Quenching of Tb^(3+) Emissions in Y_2O_2S Nanocrystals

制备了Tb^(3+ )浓度不同而粒径相同的一系列纳米晶Y2 O2 S。由于表面态对发光的猝灭作用 ,Tb3 + 离子5D3发光的寿命与体材料比较明显缩短。研究了5D3和5D4 能级发光的浓度猝灭 ,发光强度与浓度的关系以及发光的衰减曲线都表明 :5D3的浓度猝灭是电偶极 电偶极相互作用引起的 ,而5D4 的浓度猝灭是交换相互作用引起的。

It has been reported recently that some Eu 3+ doped nanocrystalline silicate and oxide were with higher quenching concentrations in comparison with the corresponding bulk materials. Computer simulation has shown that the size confinement and the existence of high density surface states affected significantly the quenching processes of the rare earth dopants in nanoparticles. To understand the feature of the energy transfer process in rare earth doped nanoparticles is important for further seeking applicable nano phosphors . This paper reported, the preparation of a series of Y 2O 2S∶Tb 3+ nanocrystals with uniform sizes and varied Tb 3+ concentrations. The mean size of all the samples prepared was evaluated, based on the X ray diffraction pattern, to be about 20nm. Emission spectra of Tb 3+ in nanocrystalline Y 2O 2S with different Tb 3+ concentrations were measured under 257nm excitation. With increasing Tb 3+ concentration, the luminescence intensity of both the 5D 4 → 7F J and 5D 3 → 7F J transitions increases at first and then decreases. Emission intensities reach their maximum at the Tb 3+ concentration of 0 6% for the 5D 3 emission and of 6 4% for the 5D 4 emission. The lifetime of the 5D 3 level is 0 31ms in the sample with 0 065% Tb concentration, comparably shorter than 0 78ms in bulk Y 2S 2O∶0 3%Tb. This fact indicates that the surface states do act as the quenching centers for the luminescence , and the increasing of quenching concentration comes probably from the lower quantum efficiency of the nanocrystals. The dependences of the intensity on Tb concentration and the decay curves of both 5D 3 and 5D 4 emissions fit with theory. The quenching of the 5D 3 state is governed by dipole dipole interaction, while that of the 5D 4 state by exchange interaction. Both the intensity and temporal analyses coincide and result in the same conclusion. Similar to bulk material, concentration quenching of the 5D 3 state is due to cross relaxation . The mechanism of the concentration quenching of the 5D 4 state is that the energy migrates among the Tb ions and is trapped finally by quenching centers, most likely, the surface states.