Quantum Dot-Polymer Architectures by Two-Photon Polymerization: From 4D Microfabrication to Quantum Light Sources

Solid-state nanoemitters, or quantum dots (QDs), exhibit high quantum yield, tunable light emission, and exceptional photo-stability, making them ideal for integration into polymers and enabling the fabrication of devices with tailored optical properties. Combining QD-doped photopolymers with two-photon polymerization (2PP) enables the fabrication of fluorescent 3D complex objects with nanometric resolution. To avoid QD agglomeration, which would hinder the device's optical performance, different strategies for achieving homogeneous particle dispersion within the polymer matrix are analyzed. Notable approaches include surface modifications, dual-functional QDs serving as photoinitiators and fluorophores, and resin additives. Depending on the protocol employed, the QDs enable sub-wavelength resolution and precise structuring during the manufacturing, by interacting with both the photopolymer and the laser beam. These physicochemical phenomena are also systematically investigated. Finally, this review provides a comprehensive examination of the characteristics and applications of QD-based optical devices, including photoluminescent security tags and PUFs, QD-integrated photonic crystals (PCs), stimuli-responsive 4D sensors, multicolor metamaterials, near-infrared (NIR) filters, and light nanosources, including single photon sources. The fabrication strategies of plasmonic light nanosources are investigated as well. The various fabrication approaches for these devices are critically analyzed and systematically compared to highlight their respective advantages, limitations, and potential for future advancements.