Near-infrared photoluminescent hybrid structures based on freestanding porous silicon photonic crystals and PbS quantum dots

Light–matter interaction in hybrid systems made of fluorophores embedded into a microcavity (MC) attracts much attention. Depending on the coupling strength between the components, either photoluminescence (PL) enhancement or hybridization of the luminophore energy levels with the MC eigenmode resulting in two hybrid energy states occurs in these systems. This effect can be used in various practical applications: enhancing Raman scattering, increasing conductivity, obtaining Bose–Einstein condensates at room temperature, etc. Hybrid structures emitting in the near-infrared (NIR) range can be used in biomedical applications for exciting and detecting radiation within the transparency window of biological tissues. Here, we have developed hybrid photoluminescent structures based on porous silicon photonic crystals (PhCs) and PbS quantum dots (QDs) emitting in the NIR range. The freestanding PhC-based MCs were obtained by electrochemical etching of monocrystalline Si. Comparison of the PhC reflectance spectra before and after exfoliation from the substrate, as well as after thermal oxidation, showed a 100-nm blue shift, other parameters being almost unchanged. After embedding QDs, we observed narrowing of their PL spectrum compared to the QD solution. We attribute this to the Purcell effect and weak coupling between the QD exciton and MC eigenmode. Thus, our hybrid structures exhibit weak light–matter coupling in the NIR range, which provides the basis for new nanophotonic biosensor systems. In addition, they are freestanding, thus offering prospects for designing sensors with the option of pumping analytes through the porous structure.