摘要
利用胶体化学共沉淀方法制备了纳米ZnS∶Mn2 + 乙醇溶胶 ,观察到Zn2 + 的引入对内部Mn2 + 的4T1→6A1跃迁的 5 80nm橙色发光有激活作用 ,而外加的Mn2 + 对该橙色发光有猝灭作用。Zn2 + 的吸附通过形成单层ZnS壳 ,减少了表面猝灭中心 ,从而使发光强度增加 ,这种表面猝灭中心最有可能是来自表面S2 -孤对电子的悬空键。Mn2 + 的猝灭过程不能用纯粹动态的猝灭过程来描述 ,Mn2 + 本身很可能就是橙光的猝灭中心。考虑到Mn2 + 在颗粒表面上的按泊松分布 ,并假设单个Mn2 + 能 1 0 0 %猝灭Mn2 + 5 80nm发射 ,理论与实验数据很好地符合。通过对猝灭数据的拟合 ,估算出的颗粒尺寸小于用有效质量近似模型算得的 3 .1nm ,分析了可能的原因。
It was observed that Zn^(2+) and Mn^(2+) additives played the activators and quenchers for the orange emission of colloidal ZnS∶Mn^(2+) nanoparticles, respectively. The time decay curves of Mn^(2+) 580 nm emission are nonexponential and become slower as Zn^(2+) is added, faster as Mn^(2+) added. On the basis of Langmuir isotherm model, the adsorption-desorption equilibrium constant K is obtained to be 2.9×10~4(mol/L)^(-1). The activation process resulted from the formation of monolayer ZnS outside of nanoparticles, which blocked the nonradiative pathways related to the dangling bonds of lone pairs on surface S^(2-). It is worth noting that the blue emission is also activated on introduction of Zn^(2+), indicating the original quenchers eliminated by the passivation of the surface through forming the ZnS shell can quench both the blue and the orange emission bands. It is not appropriate to describe the quenching process aroused by the addition of Mn^(2+) using the standard Stern-Volmer model. Considering Poisson statistics and assuming that one Mn^(2+) is sufficient for 100% quenching for orange emission, the reasonable linear plot is obtained. The average size of nanoparticles is 2.7 nm less than that calculated within the framework of effective mass approximation (EMA) model. The plausible reasons are as follows: 1. the increase of E_g owing to quantum confinement effect is overestimated by EMA; 2. the assumption that one Mn^(2+) is sufficient for 100% quenching of orange emission does not consist with the actual situation on the ZnS∶Mn^(2+) colloids. The quenching centers induced by the addition of Mn^(2+) may probably be Mn^(2+) themselves adsorbed on the surface of nanoparticles, which interact with the interior Mn^(2+) to perform Mn-Mn energy migration within short distance. Such opinion and the formation of the manolayer of ZnS on the surface is supported by the fact that the orange emission intensity is almost unchanged with the addition of Mn^(2+) after the activation process has taken place due to the addition of Zn^(2+). Surface or surface states play a crucial role on the optical properties of nanoparticles due to the relatively larger (surface)(-to-volume) ratio compared to the bulk. We expect the results may help to approach the nature of the mechanisms that surface or surface states dramatically affect the optical properties of nanoparticles.
出处
《发光学报》
EI
CAS
CSCD
北大核心
2004年第1期72-76,共5页
Chinese Journal of Luminescence
基金
国家自然科学基金 ( 5 0 172 0 47)
中国科学院百人计划资助项目
