# Photoluminescence of Rhodamine from Nano-Confinement Inside 3D Sculptured Coatings

## TL;DR

This paper studies how rhodamine's light emission changes when confined in nano-structures made by a special coating technique.

## Contribution

The study reveals how nano-confinement affects fluorescence lifetime and molecular orientation without rotational hindrance in liquid state.

## Key findings

- Fluorescence lifetime shortened by ~10% in liquid-filled nano-cavities without rotational hindrance.
- Dried structures showed 89% rotational hindrance along the ordinary axis and less than 57% along the extraordinary axis.
- Light intensity localization in nanogaps was modeled, showing efficient energy deposition in low refractive index regions.

## Abstract

The effect of the confinement of fluorophores (rhodamine 6G) in nano-cavities of porous 3D sculptured coatings made by glancing-angle deposition (GLAD) was investigated by fluorescence-lifetime imaging microscopy (FLIM). Shortening of fluorescence/ photoluminescence lifetime by ∼10% was observed from the dye-permeated (in liquid) structure; however, there was no rotational hindrance of dye molecules. When dried, a strong rotational hindrance 89% was observed for the orientation along the ordinary optical axis (slow-axis), and the hindrance was smaller than 57% for the extraordinary direction (fast axis). Light-intensity distribution inside the nano-structure with a form birefringence was numerically modeled using plane-wave illumination and a dipole source. Nanoscale localization of light intensity due to dipole nature I∼1/radius6 and boundary conditions for E-field allows efficient energy deposition inside the region of lower refractive index (nanogaps).