Thermal enhanced NIR-NIR anti-Stokes emission in rare earth doped nanocrystals

TL;DR

This study investigates how temperature and surface effects influence anti-Stokes emissions in rare earth doped nanocrystals, achieving over two orders of magnitude brightness enhancement without quenching.

Contribution

The paper provides a systematic analysis of phonon generation and surface effects, demonstrating significant emission enhancement in Yb3+/Nd3+ doped nanoparticles.

Findings

Phonon generation correlates with increased anti-Stokes emission.

Surface moisture release is not the main cause of emission enhancement.

Nanoparticle brightness increased by over two orders of magnitude.

Abstract

Nanoparticles with anti-Stokes emissions enable many sensing applications, but their efficiencies are considerably low. The key to enable the process of anti-Stokes emissions is to create phonons and assist the excited photons to be pumped from a lower energy state onto a higher one. Increasing the temperature will generate more phonons, but it unavoidably quenches the luminescence. Here by quantifying the number of phonons being generated from the host crystal and at the surface of Yb3+/Nd3+ co-doped nanoparticles, we systematically investigated mechanisms towards the large enhancements of the phonon-assisted anti-Stokes emissions from 980 nm to 750 nm and 803 nm. Moreover, we provided direct evidence that moisture release from the nanoparticle surface at high temperature was not a main reason. We further demonstrated that the brightness of 10 nm nanoparticles were enhanced by more than two orders of magnitude, standing in stark contrast to the thermal quenching effect.