SnSe_(2)量子点复合凝胶玻璃非线性光学性能研究

Nonlinear optical properties of SnSe_(2) quantum dot composite gel glass

由典型的二维层状材料衍生而来的量子点由于其独特的非线性光学(NLO)性能而引起了科学界的广泛关注,但绝大多数研究仍集中在液相基质中,不利于材料化和器件化。文中采用溶胶-凝胶法,将尺寸均一、分散均匀的SnSe_(2)量子点引入具有良好理化性能和光学透明性的二氧化硅凝胶玻璃基质中。采用透射电子显微镜(TEM)、场发射扫描电子显微镜(FESEM)、拉曼(Raman)光谱和紫外可见吸收光谱(UV/Vis)对所得SnSe_(2)量子点复合凝胶玻璃的形貌、组成、结构和线性光学性能系统表征。并采用开孔Z-扫描法对SnSe_(2)量子点复合凝胶玻璃在纳秒和皮秒激光脉冲下的非线性光学性能进行了研究。结果表明,当激光脉宽皮秒转变为纳秒时,SnSe_(2)量子点复合凝胶玻璃出现了从饱和吸收(SA)和反饱和吸收(RSA)的转变。且与相对应的悬浮液相比,SnSe_(2)量子点引入凝胶玻璃基质中后,其在皮秒下的SA和纳秒下的RSA性能均有所提高。此外,采用泵浦-探测技术和瞬态吸收光谱研究了SnSe_(2)量子点复合凝胶玻璃的超快载流子动力学过程。计算得到的SnSe_(2)量子点复合凝胶玻璃的NLO参数和弛豫时间与已报道的低维材料相当,证明该材料在非线性光学领域具有潜在的应用前景。

Objective Quantum dots derived from typical two-dimensional layered materials have attracted widespread attention due to their unique optoelectronic properties.Compared with two-dimensional layered nanomaterials,quantum dots generally have better photochemical stability,higher solubility,and enhanced nonlinear optical(NLO)effects.However,most of the reported NLO performance of quantum dots prepared based on twodimensional layered materials focused on liquid-phase matrices.Although liquid matrix can quickly restore quantum dots after laser excitation,providing convenience for the study of nonlinear optical properties and mechanisms,which is not conducive to the material and device development of nonlinear optical materials.In addition,prolonged exposure of quantum dot suspensions to air inevitably leads to aggregation and structural damage,resulting in a decrease in their NLO performance.Therefore,if quantum dots can be introduced into the solid matrix,they can effectively prevent aggregation and isolate contact with air,thus effectively solving the above problems.In this paper,the two-dimensional layered tin diselenide(SnSe_(2))crystal is used as raw material,and SnSe_(2) quantum dots with uniform size and homogeneous dispersion were synthesized using liquid phase exfoliation method.Subsequently,the resulted SnSe_(2) quantum dots were introduced into the silica gel glass matrix with good physical and chemical properties and optical transparency by sol-gel wet chemical technology,and obtained SnSe_(2) quantum dot composite gel glass.And the potential application of the SnSe_(2) quantum dot composite gel glass in the field of nonlinear optics was explored.Methods The morphology,composition,structure and linear optical properties of the SnSe_(2) quantum dot composite gel glass were systematically characterized by transmission electron microscopy(TEM),field emission scanning electron microscopy(FESEM),Raman spectroscopy and ultraviolet visible absorption spectroscopy(UV/Vis).The nonlinear optical properties of SnSe_(2) quantum dot composite gel glass under nanosecond and picosecond laser pulses were studied by open-apertures Z-scan technique.In addition,the ultrafast carrier dynamics of SnSe_(2) quantum dot composite gel glass was explored by pump-probe technique and transient absorption spectroscopy.The NLO parameters and relaxation time of SnSe_(2) quantum dot composite gel glass were deduced using Eq.(2)-(6)and Eq.(7),respectively.Results and Discussions SnSe_(2) quantum dots with uniform size and homogeneous dispersion were successfully introduced into silica gel glass by sol-gel method(Fig.3(c)and Fig.4),and the resulted composite gel glass with uniform doping and high transmittance(Fig.3(a)).Interestingly,when the laser pulse width changes from picosecond to nanosecond,the NLO absorption of SnSe_(2) quantum dots composite gel glass changes from saturated absorption(SA)to reverse saturated absorption(RSA)(Fig.6),and the SA performance of SnSe_(2) quantum dots in gel glass matrix under picosecond and RSA response under nanosecond is improved as compared to SnSe_(2) quantum dots suspension(Fig.7).By experimentally fitting the obtained kinetic curve with a double exponential decay function,two different time constants of carrier relaxation processes were obtained.The relaxation time ofτ_(1) andτ_(2) are 4.9-28.66 ps and 288.64-726.28 ps,respectively,in the wavelength of 500-640 nm(Fig.8(d)).The rapid recovery process(τ_(1))may be due to electron relaxation in the conduction band,while the slow recovery process(τ_(2))may come from the recombination of electron hole pairs.The NLO parameters(Tab.1)and relaxation time(Tab.2)of SnSe_(2) quantum dot composite gel glass are comparable to that of reported lowdimensional materials,confirming the prepared composite gel glass are a promising material for use in photonic devices.Conclusions SnSe_(2) quantum dots with uniform size and uniform dispersion were introduced into silica gel glass by sol-gel method,and composite gel glass with uniform doping and high transmittance was prepared.And the morphology,composition,structure,and linear optical properties of the synthesized composite gel glass were systematically characterized.SEM,EDX and Raman spectra results confirmed that SnSe_(2) quantum dots have been successfully introduced into gel glass matrix.The nonlinear optical effects of SnSe_(2) quantum dot composite gel glass with ps and ns pulse widths were investigated under 532 nm laser pulses.The results show that when the laser pulse width changes from ps to ns,the nonlinear absorption of SnSe_(2) quantum dot composite gel glass undergoes a transition from SA to RSA.The mechanisms of SA and RSA were also explained in detail.In addition,compared with SnSe_(2) quantum dot suspension,the SA and RSA response enhance after incorporating into solid state matrix.The mechanism of enhancing nonlinear optical effects is also explained by the matrix effect.The ultrafast carrier dynamics of SnSe_(2) quantum dot composite gel glass was further studied by pump probe technique and transient absorption spectroscopy.The calculated relaxation time is equivalent to that of reported low-dimensional materials,which proves that SnSe_(2) quantum dot composite gel glass shows great potential application prospects in the field of ultrafast optoelectronics.Our work would provide theoretical and material basis for the preparation of novel composite nonlinear optical materials with excellent performance.