# Spectrally Resolved Dynamics of Delayed Luminescence in Dense Scattering Media

## TL;DR

The paper studies how light is emitted over time in highly scattering materials, revealing how their structure affects the duration and spectrum of the emission.

## Contribution

The study introduces a new model for spectrally resolved delayed luminescence in dense scattering media, linking emission properties to mesoscale structural effects.

## Key findings

- Delayed luminescence in TiO2 films shows non-exponential decay and spectral evolution over time.
- DL lifetime increases up to 6 seconds due to multiple reabsorption processes in redshifted emissions.
- Mesoscale inhomogeneities in random media strongly influence DL intensity and duration.

## Abstract

Highly scattering media have garnered significant interest in recent years, ranging from potential applications in solar cells, photocatalysis, and other novel photonic devices to research on fundamental topics such as topological photonics, enhanced light–matter coupling and light confinement. Here, we report measurements of spectrally and time-resolved delayed luminescence (DL) in highly scattering rutile TiO2 films. The complex emission kinetics manifests in the non-exponential decay of photon density and the temporal evolution of the spectral composition. We found that while the energy levels of TiO2 nanoparticles broadly set the spectral regions of excitation and emission, our results demonstrate that the DL intensity and duration are strongly influenced by the inherent multiple elastic and inelastic processes determined by the mesoscale inhomogeneous structure of random media. We show that the lifetime of DL increases up to 6 s for the largest redshift detected, which is associated with multiple reabsorption processes. We outline a simple model for spectrally resolved DL emission from dense scattering media that can guide the design and characterization of composite materials with specific spectral and temporal properties.