Spin-dependent photoluminescence in carbon-based quantum dots

TL;DR

This study demonstrates room temperature, spin-dependent photoluminescence modulation in carbon-based quantum dots using magnetic fields, revealing potential for quantum sensing and imaging in biological contexts.

Contribution

The paper reports the first observation of spin-dependent PL modulation in CQDs at room temperature, including synthesis with amino acids and detection of ESR signals indicating radical pair mechanisms.

Findings

Magneto-PL effect up to 1% observed in CQDs.

ESR detected with g ≈ 2, indicating radical pair processes.

Magneto-PL contrast decreases with paramagnetic species.

Abstract

The ability to modulate the photoluminescence (PL) of nanomaterials via spin-related effects is vital for many emerging quantum technologies, with nanoscale quantum sensing and imaging being particular areas of focus. Carbon-based quantum dots (CQDs) are among the most common forms of luminescent nanomaterials, appealing due to their ease of synthesis, tunability through organic chemistry, high brightness, and natural biocompatibility. However, the observation of room temperature, spin-dependent PL has remained elusive. Here we report on the observation of PL modulation of CQDs by magnetic fields ($\sim 10$ mT) under ambient conditions. We synthesize a series of CQDs using 19 different amino acids, which have a range of PL emission spectra and exhibit a clear magneto-PL effect (up to $\sim 1$% change). Furthermore, an electron spin resonance is detected in the PL with a g-factor of g $\approx$ 2, suggesting a process similar to the radical pair mechanism is responsible. Finally, we show that the magneto-PL contrast decreases in the presence of paramagnetic species, which we attribute to an increase in magnetic noise-induced spin relaxation in the CQDs. Our work brings new functionalities to these commonly used and biocompatible luminescent nanoparticles, opening new opportunities for in situ quantum sensing and imaging of biological samples.