CHEAH, Kok Wai - Head and Chair Professor


B.Sc. Hons, ARCS, M.Sc., DIC, Ph.D., CSci, CPhys. FinstP
Imperial College of Science, Technology and Medicine, London University.

Honorary Associate Professor of The University of Hong Kong, Hong Kong.
Senior Visiting Professor of Fudan University, Shanghai, China
Adjunct Professor of Sun Yat-sen University, Guangzhou, China
Visiting Professor of Jinan University, Guangzhou, China

Contact: Rm. T924
Tel: (852) 3411-7029
Website: Centre for Advanced Luminescencei Materials, Photonic Materials Laboratory

  1. Optical Properties of Organic Complexes
    Organic complexes like conjugated Oligofluorenes are investigated for their strong non-linear optical properties. We show that multi-photon up-conversion takes place efficiently and their optical limiting absorption coefficients were measured. Figure 1 shows 3-photon up-conversion photoluminescence and lasing spectra of an Oligofluorene complex.

    Figure 1

  2. Porous Silicon
    We have developed plasmonic LED emitting in 337.1nm (UV A). The LED has potential application in bio-agent detection and germicide, and flat panel display. Figure 2.1 shows the LED. When dyes are placed on top of the LED, visible LED of difference colour can be obtained. Figure 2.2 shows a blue LED derived using a blue organic dye. The UV LED has an US patent (60/364,683).

    Strong luminescence from near-IR to near UV can be obtained from rare earth doped porous silicon (Patent Number: 6,056,868). The figure 2.3 shows luminescence intensity comparison of Er/Yb doped porous silicon to Er doped porous silicon and Er2O3 at 1.54£gm. Figure 2.4 shows efficient up-conversion emission of Er/Yb doped porous silicon, emitting at RED, GREEN, and UV. The excitation wavelength of both linear and non-linear spectra is 980nm.

    Figure 2.1

    Figure 2.2

    Figure 2.3

    Figure 2.4

  3. Anisotropic Metamaterial
    Superlens and optical bistability properties of multi-layer anisotropic metamaterials are being studied. In superlens, we studied a system consisting of two complementary anisotropic metamaterials that can support the ordinary evanescent modes and focus these modes through negative refraction to form a sub-wavelength image. Theoretical result shows that this is feasible and we are working on the experimental verification. Fig. 3 shows Magnetic flux density distribution in C-slab superlens at , a pair of slits with width of 30nm and center to center separation 60nm is illuminated by a normally incident TM wave along the positive direction of x axis, resolvable super-resolution images of the slits are obtained at the image plane of the C-slab.

    Figure 3

  4. Solid State Light Phosphor
    Using a hybrid of organic and inorganic phosphors, a white light phosphor is developed for InGaN UV LED. The phosphor has excellent CIE index and Colour Rendering Index. Figure 4 shows the CIE diagram of a series white light LED we have produced. The phosphor is ready for commercial application.

    Figure 4