Preparation And Properties Study Of Low Angle Dependent 1D Photonic Crystal Films

Compared with traditional photonic crystals,the structure of 1D magnetic photonic crystals has continuous and obvious angle dependence,which makes it have broad application prospects in the fields of anti-counterfeiting and display.However,with the rapid development of personalized display,advanced anti-counterfeiting and camouflage materials,the development of photonic crystal materials that can maintain color stability within a certain angle range is of great significance.In this paper,the orientation direction of the one-dimensional chain photonic structure can be adjusted arbitrarily with the direction of the magnetic field,and combined with the bottom-up stacking method,two-layer photonic crystal film with asymmetric color development with angle and three-layer photonic crystal film with low angle dependence were prepared respectively.Their asymmetric color rendering and low angle-dependent color rendering mechanism and optical properties were investigated.The main work of the paper is as follows:（1）The orientation of the photonic structures in the photonic crystal film was controlled and fixed by magnetically induced assembly and ultraviolet photopolymerization,and a double-layer photonic crystal film with asymmetric color development with the observation angle was prepared by a bottom-up stacking method.The photonic structures embedded in the bottom film of the bilayer film are vertically oriented and the photonic structures embedded in the upper film are tilted 30°to the right.When the sample is tilted left and right along the horizontal axis,the optical properties show a clear angle-dependent change on the left side and a low angle-dependent change in the 0°～30°tilt angle range on the right side,thus showing an asymmetrical color display effect;When the sample is tilted left and right along the vertical axis,it exhibits obvious angular dependence,thus showing symmetrical color development;In addition,when the observation angle is inclined to the right by 30°and the sample rotates by 360°,its structural color exhibits a variation law of red-orange-yellow-orange-red.Furthermore,the effects of changing the particle size of Fe₃O₄@PVP particles and the inclination angle of the photonic structure embedded in the upper film on the optical properties of the bilayer photonic crystal film were investigated:As the Fe₃O₄@PVP particles size becomes smaller,the initial structural color of the asymmetric color rendering of the photonic crystal film will blue-shift;As the orientation angle of the chain-like photonic crystal structure in the top layer increases from 30°to 45°,the low-angle-dependent interval on the right side of the photonic crystal film increases,resulting in enhanced asymmetric display effects on both sides.The double-layer photonic crystal shows rich color changes with the change of tilting mode and angle,and the anti-counterfeiting label based on the asymmetric color-developing double-layer photonic crystal film exhibits excellent visual anti-counterfeiting effect.（2）On the basis of the double-layer photonic crystal film,the photonic crystal film with low angle dependence was fabricated by stacking the third film embedded with photonic structures with different tilt angles.Different from the traditional low-angle-dependent photonic crystal film,the system does not need to introduce black light-absorbing substances or destroy the order of the photonic structure,but derives from the diffraction superposition effect of the photonic structures in different layers on the incident light.When the structural feature of the photonic crystal film is that the chain-like photonic crystal structures in the lower layer are vertically oriented,and the orientation directions of the chain-like photonic crystal structures in the upper layer and the middle layer are inclined by 30°to the left and right along the normal direction,respectively,which exhibits low-angle-dependent optical changes in the tilt range of-30°～30°and obvious angle-dependence outside this angle range.And it can be regulated by changing the tilt angle of the photonic structure in the top layer during the preparation process.When the tilt angle of the photonic nanochains in the top layer is deflected from-30°to 60°,the low angle-dependent interval of the photonic crystal film is gradually deflected from-30°～30°to 0°～60°,showing a wide range of low angular dependence on one side and an obviously angular dependence on the contralateral side.In addition,as the size of the assembly unit Fe₃O₄@PVP becomes smaller,the range of the low-angle-dependent region of the constructed photonic crystal film remains unchanged;however,the overall angular-dependence of the optical properties decreases due to the blue-shift of the initial structural color.