# Photochromic control of the spontaneous emission of a dipole emitter placed at the apex of a silver nanocone

Reegan Aruldoss, Anne-Laure Baudrion, Pierre-Michel Adam

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Reegan Aruldoss, Anne-Laure Baudrion, Pierre-Michel Adam. Photochromic control of the spontaneous emission of a dipole emitter placed at the apex of a silver nanocone. GDR Plasmonique Active, Jun 2021, Troyes, France. hal-03610685

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Submitted on 16 Mar 2022

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# GDR Plasmonique Active

2021, June 28th – 29th Troyes, France

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# Photochromic control of the spontaneous emission of a dipole emitter placed at the apex of a silver nanocone

Reegan ARULDOSS,¹Anne-Laure BAUDRION¹, Pierre-Michel ADAM¹

¹ Laboratoire Lumière, nanomatériaux, nanotechnologies (L2n), ERL - CNRS 7004, Université de Technologie de Troyes (UTT), Troyes, France.

reegan.aruldoss@utt.fr

## Introduction

The control of the spontaneous emission of emitters using plasmonic structures, either to enhance or quench the photoluminescence, mainly depends on the spectral overlap between the emitter's emissions/absorption and the Localized Surface Plasmon Resonance of the plasmonic structures [1]. As photochromic molecules can reversibly change from a transparent state to a colored one by absorbing respectively UV and visible radiations, they were considered as excellent optical switches [2]. Lamri et al [3] in 2019, has experimentally demonstrated an optical control of the Quantum Dots (QDs)-metal nanoparticle coupled system leading to an optical switch between quenching and enhancement of QD photoluminescence. However, the enhancement factor of this previous system was not optimized as many QDs were placed randomly on top of an array of silver nanocylinders. But herein, we propose to use nanocones, as they are capable of dramatically increasing the quantum efficiency of emitters placed at the tip [3].

## Advantage of Nanocone over Nanocylinder

<figure><img src="image_3.png" /><figcaption>Vertical Polarization</figcaption></figure>

<figure><img src="image_4.png" /></figure>

* The Quality of plasmon resonance is better for Nanocones.

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

* The plasmon resonance of Nanocone can be tuned in the same wavelength range of Nanocylinder with lesser material loss.

## Electric Near Field Enhancement

<figure><img src="image_7.png" /></figure>

* Higher near field enhancement for vertical plasmon mode (tip mode) of Nanocones.

* Highly confined electric field around the tips.

## Conclusion

* Conical nanoantennas are better than nanocylinders for both excitation and emission enhancement

* Plasmonic enhancement and quenching can be achieved.

* Active control of spontaneous emission of emitter coupled to nanoantennas including nanocone are achieved using photochromic medium

## References

* [1] Viste, P. et al., ACS Nano 4 (2), 759-764 (2010).

* [2] Lamri, G. et al., Nanoscale 11, 258-265 (2019).

* [3] Matsuzaki, K. et al., Scientific report 7, 42307 (2017)

* [4] A-L Baudrion et al., Nano Lettre 13, (2013)

## Photochromic Molecule

<figure><img src="image_8.png" /></figure>

Structural change of photochromic molecule before (Spiropyran) and after (Merocyanine) UV irradiation.

(a) Extinction spectra of the two states of photochromic molecules. (b) changes in the refractive index (black) and extinction coefficient (red) before and after photochromic transition [4]

<figure><img src="image_9.png" /><figcaption>Scheme of the Simulated System</figcaption></figure>

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* There is nearly 8 fold enhancement in radiative decay rates of dipole emitter (at peak 570nm) above nanocone with D=60 nm in the transparent state of the photochromic medium.

* The plasmon resonance of the nanocone in MC is red shifted compared to the SPY, and it can be observed in the Purcell factor graphs.

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