ZnSe Hollow Nanospheres-Based NIR Antireflection Coatings For ZnSe Substrates

Znic selenide(ZnSe)is widely used in the infrared laser optics,due to its low absorption coefficient in a broad range from near IR(NIR)to mid IR(MIR),low variation of refractive index with temperature and wavelength,not liable to deliquesce,and high thermal shock resistance.However,because of its high reflective index(n = 2.46),the reflection of the optical widows and lenses made of ZnSe is quite high and less than 70% of light could be transmitted.Hence,an antireflection layer must be coated on ZnSe substrates to enhance the transmission and thus the performance of optical systems.At present,antireflection coatings(ARCs)usually employ a complicated design,where multilayer of different materials with high and low refractive indices are alternately superimposed on ZnSe substrates.It can't realize high transmission from NIR to MIR,and can't enable good adhesion between antireflection layer and substrate.Besides,the size of HNSs ought to be smaller than 100 nm,to avoid scattering loss of NIR light.So,ZnSe hollow nanospheres(HNSs)are the ideal materials assembled as ARCs for Zn Se substrates.However,there is no report about the preparation of ZnSe HNSs and its antireflection performance.In this paper,Zn nanoparticles were prepared by laser ablation with uniform size(42 nm),hexagonal crystal structure and good dispersion.Then,ZnSe HNSs were synthesized by hot-injection with Zn nanocrystals as templates,which show zinc blende crystal structure,uniform size(60 nm),with shell thickness of 10 nm,good dispersion and crystallinity.The kinetics of ZnSe HNSs formation was found to coincide well with the nanoscale kirkendall effect.The concentration of selenium in solution,the reaction temperature and time have important role in the formation kinetics of ZnSe HNSs.Furthermore,the as-prepared colloidal ZnSe HNSs were assembled onto ZnSe substrates to form single-index ARCs through the spin-coating method and annealed.With the ZnSe HNSs-based ARCs,the transmission of ZnSe substrates was remarkably enhanced in the NIR region by nearly 20%,achieving a value of 89% at 840 nm.Besides,the ZnSe HNSs-based ARCs show superior mechanical stability.