Fabricated by femtosecond laser pulses at wavelength λ of 780nm, the feature size of two-photon polymerization using SCR500 was reduced to λ∕50. Lines with sub-25-nm width were produced by controlling the incident laser power and the laser focus scan speed up to 700μm∕s. Based on repolymerization between two structures close to each other, the feature size was further reduced to ∼15nm, which demonstrated the potential for three-dimensional nanofabrication with high spatial resolution.

Microstereolithography (MSL) is an emerging technology, which is expected to play a key role in the fabrication of micro-and nanoelectronic machines and micro-and nanoelectromechanical systems (MEMS/NEMS).[1] Of the various MSL techniques, multiphoton photopolymerization (MPP) [2][3][4][5][6] has attracted widespread interest owing to its potential use in fabricating intrinsic 3D microstructures such as 3D photonic crystals (PhCs). [7][8][9][10][11] Much effort at developing MPP-MSL has been devoted to improving the resolution of the fabrication approaches at the nanometer scale, [12][13][14][15][16] and to achieve the fabrication of functional microstructures. [7][8][9][10][11]17,18] Photopolymerizable resins such as common photoresists have been widely used in MPP-MSL as photocurable polymeric crosslinking networks to maintain the shape of 3D microstructures after the lithography and post developing processes. To satisfy the requirements for functional MEMS/NEMS, the materials in the 3D microstructures need to be further functionalized, which offers the possibility of adding new functionality targeted at achieving novel applications for MEMS/NEMS. High-efficiency luminescent devices with micrometer-sized features, such as fluorescent microstructures, are of great interest for photonic applications. However, not much research effort has been focused on developing luminescent 3D microstructures. [19][20][21] Analogous to systems such as laser-dye-doped polymers, luminescent semiconductor-polymer nanocomposites are also attractive as luminescent polymeric materials, since various semiconductor nanoparticles (NPs) show unique tunable light emission properties arising from quantum size effects. Recent reports in the literature have focused on the synthesis and light emission properties of semiconductorpolymer nanocomposites. However, to the best of our knowledge, there have not been many reports of photoluminescent 3D microstructures of semiconductor-polymer nanocomposites and their emission properties. One major reason for this is that most nanoparticles are difficult to disperse in the photoresist resins, which tend to be highly viscous. The aggregation of NPs causes the photoresist resin to become opaque, thus degrading the ability to fabricate 3D structures by MPP-MSL techniques. To realize 3D microstructures of luminescent polymer nanocomposites and to facilitate their use as photonic microdevices, it is essential to develop a suitable method for fabricating 3D microstructures from polymer nanocomposites with size control of the embedded NPs. Such an approach is expected to enable the fabrication of color-tunable microstructures and the development of high-efficiency polymer optoelectronic devices.In our previous studies, [22] we have reported the first 3DPhCs of TiO 2 -NP-embedded polymer nanocomposites with a confirmed photonic bandgap (PBG). These PhCs have been fabricated by MPP-MSL using a Ti-ion doped urethane acrylate resin. Furthermore, we have recently demonstrated a 3D PhC based on a CdS-polymer nanoc...

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