Functionalisation of three-dimensional photonic crystals for emission control

This thesis aims to develop a platform for studies on the functionalisation of 3D PCs with active QDs as well as with nano-scale metallic coating in the NIR wavelength range. The developed functionalities of 3D PCs can be applied on emission control such as SE control and thermal emission control. As a starting point, high-quality 3D woodpile PCs are fabricated with a convenient direct laser writing method called the two-photon polymerisation (2PP) technique. This technique is able to produce 1D, 2D and 3D arbitrary structures of sub-wavelength resolution with inexpensive polymer materials. More importantly, the fabricated 3D PCs can be easily functionalised by engineering chemical compositions, incorporating functional materials, or transforming structure conformations, which give rise to a great flexibility in subsequent studies on 3D PC applications. For 3D PC applications, the matching of PBGs to the desired wavelengths is important since the PBGs are normally restricted in a specific spectral region. To this end, a structural engineering approach - a post-thermal treatment method - is proposed and demonstrated to improve the spatial resolution and engineer the stop gaps of 3D PCs, which can result in inorganic-organic 3D PCs operating from NIR to visible wavelength range. To functionalise 3D PCs with active media, the woodpile PCs are directly fabricated in a NIR QDs doped composite with 2PP. With QDs homogeneously distributed inside the structure, 3D PCs with strong partial stop gaps are realised. In addition, an infiltration method is developed to flexibly embed home-made high-quality QDs into fabricated 3D PCs. With this method, the amount of incorporated QDs can be well controlled by simply changing QD concentration or adjusting infiltration times, which greatly facilitates future studies on QDs emission control. Based on the functionalised 3D woodpile PCs incorporated with NIR QDs, control of SE with PBGs are studied. A spectral redistribution is observed from PbSe QDs infiltrated inside the PC with matched PBG. To find out the physical reason of such a spectral redistribution, a time-correlated single-photon counting system is built up to quantify the emission decay properties of QDs. Through careful analysis and comparisons, inhibition of the QDs radiation is verified in the stop gap region, indicating the feasibility for studying on emission control with polymeric 3D woodpile PCs. Moreover, the inhibition as well as the enhancement of SE from QDs inside a 3D PC are achieved in the mid-gap and at the centre of the band edge, respectively. These modifications of SE are further confirmed by consistent comparisons with the calculated decay time distributions. This study provides an effective way to tune the SE from QDs by engineering the PBG effects in a given 3D PC. Along with the studies on emission control, advanced functionalities of 3D PCs are further explored with innovative 3D silver hybrid PCs. Here the 3D hybrid PCs refer to dielectric woodpile PCs coated with nanoscale (~ 10 − 20 nm) metallic layers on the structure surfaces, which are conceptually different to conventional MDPCs. Besides the ultra-wide and complete photonic band gaps, the localised plasmon resonances (LPRs) are successfully introduced in 3D hybrid PCs. As a result, extraordinarily enhanced absorption channels are created and can be significantly tuned by structural parameters. Furthermore, 3D silver hybrid PCs with LPRs at NIR wavelengths are experimentally demonstrated with 2PP and a silver deposition method. More importantly, the scheme of creating LPRs in 3D hybrid PCs is confirmed to be applicable to a wide range of metals like gold and tungsten. The wide-range tunable LPR-enhanced absorption and the LPR-induced localised electromagnetic field provide additional modulations for photon-matter interactions. These offer a new mechanism for application of 3D PCs on thermal emission control compared with the conventional approaches with the effects of PBGs and band edges. The research conducted in this thesis is to build up solid and comprehensive studies on the functionalisation of 3D PCs in the technically important NIR wavelength range. Accompanying with the important demonstration that 3D woodpile PCs of low refractive-index are capable of modifying and engineering SE, this thesis proposes and proves a new concept to functionalise 3D PCs merged with LPRs, which can significantly enhance the structural absorption with a wide tunability. The research approaches as well as the conclusions reached in this thesis could lead to a profound understanding of the functionalisation of 3D PCs towards potential device applications in the NIR wavelength range.