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. 2020 Apr 16;10(25):14958-14964.
doi: 10.1039/d0ra02245d. eCollection 2020 Apr 8.

Core-shell silica-rhodamine B nanosphere for synthetic opals: from fluorescence spectral redistribution to sensing

Paola Lova  1 , Simone Congiu  1 , Katia Sparnacci  2 , Angelo Angelini  3 , Luca Boarino  3 , Michele Laus  2 , Francesco Di Stasio  1 , Davide Comoretto  1
Affiliations

Core-shell silica-rhodamine B nanosphere for synthetic opals: from fluorescence spectral redistribution to sensing

Paola Lova et al. RSC Adv. .

Abstract

Photonic crystals are a unique tool to modify the photoluminescence of light-emitting materials. A variety of optical effects have been demonstrated by infiltrating opaline structures with photoactive media. On the other hand, the fabrication of such structures includes complex infiltration steps, that often affect the opal lattice and decrease the efficiency of light emission control. In this work, silica nanospheres were directly functionalized with rhodamine B to create an emitting shell around the dielectric core. Simple tuning of the microsphere preparation conditions allows selecting the appropriate sphere diameter and polydispersity index approaching 5%. These characteristics allow facile self-assembling of the nanospheres into three-dimensional photonic crystals whose peculiar density of photonic states at the band-gap edges induces spectral redistribution of the rhodamine B photoluminescence. The possibility to employ the new stable structure as sensor is also investigated. As a proof of principle, we report the variation of light emission obtained by exposure of the opal to vapor of chlorobenzene.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. (a) Schematic and (b) SEM micrograph of the fluorescent silica nanospheres (average diameter 277 ± 13 nm).
Fig. 2
Fig. 2. (a) Reflectance (black curve) and transmittance (red curve) spectra of an opal fabricated via vertical-deposition on a soda-lime glass slide employing the fluorescent silica nanospheres. As expected, the optical features (i.e. reflectance peak and transmission minimum) of the photonic band gap overlap, and they are centered at 616 nm. Interference fringes are visible in the reflectance spectrum indicating the high optical quality of the obtained sample. SEM micrographs of the opal: (b) cross-section and (c) surface. In both micrographs the face-centered-cubic lattice of the nanospheres can be appreciated.
Fig. 3
Fig. 3. Photoluminescence spectra collected from the opal (full black curve) and the reference (dashed black curve) at different collection angles: (a) 0°, (b) 20° and (c) 40°. The respective transmission spectra are shown (red curves) to indicate the spectral position of the photonic band gap. (d) Photoluminescence intensity color map vs. collection angle where the dispersion of the photonic band gap induces an angle-dependent modification of the photoluminescence intensity and spectral shape.
Fig. 4
Fig. 4. (a) Photoluminescence intensity modification vs. collection angle. A value >1 indicates photoluminescence enhancement, while a value lower <1 indicates photoluminescence suppression. The curves are obtained by diving the photoluminescence spectra of the opal and the reference after normalization at a collection of 60° where the photonic band gap does not affect the photoluminescence intensity and shape. (b) Photoluminescence enhancement/suppression map vs. angle. The observed photoluminescence suppression follows the angular dispersion of the photonic band gap (see ESI Fig. S4†).
Fig. 5
Fig. 5. (a) Scheme of the chlorobenzene sensing test: the opal was inserted in a quartz cuvette directly connected to a vial containing the chlorobenzene. The opal was exposed to a constant solvent concentration of 53 mg l−1 over the test duration. (b) Photoluminescence spectra of the opal collected at 0° at increasing exposure times.
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