Nanoscale Photoluminescence Manipulation in Monolithic Porous Silicon Oxide Microcavity Coated with Rhodamine‐Labeled Polyelectrolyte via Electrostatic Nanoassembling

Zhi Chen,Gabriella Egri,Antonino A La Mattina,Aline Debrassi,Valentina Robbiano,Giuseppe Barillaro,Giuseppe Carnicella,Giuseppe M Paternò,Alessandro Minotto,Lars Dähne,Franco Cacialli,Stefano Mariani

doi:10.1002/adom.202100036

Abstract

AbstractPorous silicon (PSi) is a promising material for future integrated nanophotonics when coupled with guest emitters, 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. 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 enhancement of the photoluminescence quantum yield of the PAH‐RhoB in the PSiO2 MC with respect to the reference structure. Application of the electrostatic nanoassembling approach to other emitting dyes, nanomaterials, and nanophotonic systems is envisaged.

Highlights

The poly(allylamine hydrochloride) (PAH)-Rhodamine B (RhoB) polyelectrolyte was solubilized in water and drop cast onto the PSiO2 MC to achieve spontaneous infiltration of the nanopores with the polyelectrolyte solution (Figure 1a-iii)
Rinsing in deionized water and ethanol eliminated the excess of polyelectrolyte within the pore volume, leaving a nanometer-thick (i.e., 1.76 ± 0.17 nm, as measured on a SiO2/Si substrate) monolayer of the positivelycharged PAH-RhoB polyelectrolyte anchored to the negativelycharged inner SiO2 surface of the nanopores by electrostatic forces[33] (Figure 1a-iv)
We investigated the confinement effect of the PSiO2 MC on the PAH-RhoB emission by comparing the PL spectra of PAH-RhoB deposited via electrostatic nanoassembling within the cavity and reference structures

Summary

Introduction

Infiltration of PSi with a number of nanomaterials has been carried out to take advantage of the peculiar properties of luminescent guest materials when con-. Impregnation, functionalization, and direct one-step infiltration strategies of monolithic PSi MCs do not allow precise control of thickness and distribution of the guest materials deposited within the pores with depth This results in uneven pore filling/ coating and emitter aggregation within the porous scaffold, which leads to detrimental energy-transfer between emitters and optical scattering/losses and, in turn, to a poor manipulation of the emitter luminescence.

Results and Discussion

Conclusions

Experimental Section

Data Availability Statement