半导体量子点材料在Nd∶YAG激光辐照下的非线性光学效应(英文)

Observation of nonlinear optical effects in some semiconductor quantum dot materials using Nd∶YAG laser radiation

使用10 ns脉冲调QNd∶YAG激光器Z-scan技术测量了化学合成的无掺杂硫化锌量子点(QDs)以及掺Mn2+硫化锌量子点(QDs)的非线性光学特性,并使用透射电镜技术(TEM)以及X射线衍射法(XRD)表征合成材料的纳米结构。在室温下,分别利用UV-VIS分光光度计和分光荧光计测量了人工合成QDs胶体溶液的线性光学吸收特性以及光致发光的发射特性。样品的吸收特性表明,由于量子限制效应的影响,样品的截止吸收低于硫化锌的截止吸收。样品的光致发光特性显示,掺Mn2+的硫化锌样品显示出明显的光致发光现象,发射峰大约在580 nm;而无掺杂的硫化锌样品在紫外区辐射,发射峰大约在365 nm。对样品的UV-VIS吸收特性分析和TEMXRD分析表明,硫化锌样品的平均粒度(半径)大约为1.2 nm。分析开放光圈(OA)Z-scan技术得到的实验数据,发现在1 064 nm处两种试验样品都会发生四光子吸收(FPA)现象。拟合实验数据得到了两种试验样品的FPA系数以及FPA横截面,结果表明,ZnS QD的FPA横截面的计算值是4.9×10-106cm8.s3.photon-3,比硫化锌的FPA横截面大了5个数量级,而且人工合成的ZnS QD也有光学限制的性质。掺Mn2+离子的样品具有大的FPA横截面和在可见光区有高的发光效率这两个特点,使得该材料适合用于多光子荧光成像。

Nonlinear optical（NLO） properties of the colloidal solutions of chemically synthesized undoped and Mn2＋ doped ZnS Quantum Dots（QDs） in methanol are measured by using a Q-switched 10 ns pulsed Nd∶YAG laser radiation by the Z-scan technique.The nanostructures of the synthesized materials are characterized by using different characterization tools,such as Transmission Electron Microscopy（TEM） and X-ray Diffraction（XRD） analysis.Linear optical absorption and Photoluminescence（PL） emission characteristics of the colloidal solutions of the synthesized QDs are measured at room temperature by using a UV-visible spectrophotometer and a spectrofluorimeter,respectively.The absorption characteristics of the samples show that the absorption cut-off of the samples is below that of the bulk ZnS due to the quantum confinement effect.Photoluminescence emission characteristics measured at room temperature show that the Mn^2＋ doped ZnS sample exhibits its visible PL emission peak at 580 nm,whereas the undoped ZnS sample emits in the ultraviolet region peak at 365 nm.The average particle size（radius） of the as-prepared ZnS sample is 1.2 nm as determined from the measured UV-visible absorption characteristics as well as from TEM and XRD data analyses.By analyzing the experimental data obtained by the Open Aperture（OA） Z-scan technique,it is found that the Four-photon Absorption（FPA） takes place at 1064 nm wavelength in both the studied samples.FPA coefficients and FPA cross-section of both the samples are extracted by fitting the experimental data with the available analytical expression.It is found that the calculated value of FPA cross section of ZnS QD is 4.9×10^-106 cm^8·s^3·photon^-3,which is five orders of magnitude larger than that of bulk ZnS.Optical limiting property of the synthesized ZnS QD is also presented.The simultaneous presence of large FPA cross section and large luminescence efficiency in the visible region in Mn2＋ doped sample would render this material as a good candidate for multiphoton fluorescence imaging applications.