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Open Access Publications from the University of California

Magnetically Responsive Photonic Structures

  • Author(s): Hu, Yongxing
  • Advisor(s): Yin, Yadong
  • et al.

Magnetically responsive photonic crystals (MRPCs), whose colors can be controlled by external magnetic field, have drawn lots of attention during the past two decades. They are highly desirable for the potential applications, such as sensors and tunable color displays. However it remains difficult to fabricate MRPCs with convenient control, fast response, excellent reversibility and easy integration into advanced devices.

In my thesis work, I have focused on the development of novel magnetically responsive photonic structures with rapid and full reversibility. First, superparamagnetic magnetite (Fe3O4) colloidal nanocrystal clusters (CNCs) have been synthesized and employed as building blocks to construct colloidal photonic crystals. The one dimensional periodic chainlike structure whose diffraction can be moved across the entire visible spectral region can be achieved by the application of an external magnetic field. The precise control, fast response and the fully reversible optical properties show great potential in applications such as responsive color displays or sensors.

The assembled structures have been studied by using a method that combines magnetic assembly with sol-gel processes to physically fix individual photonic chains. The resulting nanochains exhibit magnetically responsive photonic properties and long-term structural/optical stability. Greatly improved magnetically responsive photonic structures with widely tunable optical properties and long-term stability can be achieved by porous silica coating on the CNCs surface by a novel water based etching method.

A new mechanism of stabilizing the magnetic photonic crystals against packing force while keeping the tunability will be shown in the thesis. By taking advantage of agarose gel as a matrix to prevent the photonic structures inside from aggregation, the system shows remarkable stability against an external magnetic field. Other features such as fast, reversible, and tunable optical response to external magnetic fields are well kept in this system.

In addition, a bistable color-reflective magnetic tunable photonic film with thermally erasable property will be presented. This film exhibits excellent cycling stability and durability over a long period. The simple fabrication process, easy control over the color change, the superior stability over cycling and prolonged field exposure, and the low cost and energy saving properties allow broad potential applications including outdoor displays.

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