Nanoscale Photoluminescence Manipulation in Monolithic Porous Silicon Oxide Microcavity Coated with Fluorescent Polyelectrolytes Via Electrostatic Nanoassembling

Porous silicon (PSi) is a promising material for future integrated nanophotonics when coupled with guest emitters [1,2], still facing challenges in terms of homogenous distribution and nanometric thickness of the emitter coating within the silicon nanostructure. Herein, it is shown that the nanopore surface of a porous silicon oxide (PSiO2) microcavity (MC) can be conformally coated with a uniform nm-thick layer of a cationic light-emitting polyelectrolyte, e.g., poly(allylamine hydrochloride) labeled with Rhodamine B (PAH-RhoB), leveraging the self-tuned electrostatic interaction of the positively-charged PAH-RhoB polymer and negatively-charged PSiO2 surface. It is found that the emission of PAH-RhoB in the PSiO2 MC is enhanced (≈2.5×) and narrowed (≈30×) at the resonant wavelength, compared with that of PAH-RhoB in a non-resonant PSiO2 reference structure [3]. The time-resolved photoluminescence analysis highlights a shortening (≈20%) of the PAH-RhoB emission lifetime in the PSiO2 MC at the resonance versus off-resonance wavelengths, and with respect to the reference structure, thereby proving a significant variation of the radiative decay rate. Remarkably, an experimental Purcell factor Fp = 2.82 is achieved. This is further confirmed by the enhance- ment of the photoluminescence quantum yield of the PAH-RhoB in the PSiO2 MC with respect to the reference structure. By building on these results, we envisage many emerging photonic applications of the electrostatic nanoassembly coating technology for introduction of foreign emitters into PSi-based photonic nano-/mesostructures, though not lim- ited to, including ultrasensitive fluorescence-enhanced optical nanosensors, nanolasers, exciton-polaritonic devices, spintronic devices, and quantum optical devices. References [1] V. Robbiano, G. M. Paterno, A. A. La Mattina, S. G. Motti, G. Lanzani, F. Scotognella, G. Barillaro, ACS Nano 2018, 12, 4536. [2] V. Robbiano, S. Surdo, A. Minotto, G. Canazza, G. M. Lazzerini, S. M. Mian, D. Comoretto, G. Barillaro, F. Cacialli, Nanomater. Nanotechnol. 2018, 8, 184798041878840. [3] Z. Chen, V. Robbiano, G. M. Paternò, G. Carnicella, A. Debrassi, A. A. La Mattina, S. Mariani, A. Minotto, G. Egri, L. Dähne, F. Cacialli, G. Barillaro, Adv. Optical Mater. 2021, 2100036 Acknowledgements Z.C. and V.R. contributed equally to this work. G.B. and Z.C. acknowledges the European Community and the Tuscany Region for their funding within the framework of the SAFE WATER project (European Union’s Horizon 2020 Research & Innovation program and the ERA-NET “PhotonicSensing” cofund – G.A. No 688735). G.M.P. thanks Fondazione Cariplo by (grant n° 2018-0979) for financial support. F.C. and A.M. acknowledge funding by EPSRC (grant EP/P006280/1, MARVEL), and G.C. and V.R. the European Community’s H2020 ETN MSCA action under grant agreement 643238 (SYNCHRONICS). F.C. acknowledges the Royal Society and the Wolfson Foundation for a Royal Society Wolfson Foundation Research Merit Award.