Development of time-resolved fluorescence spectroscopy using heralded emission spectroscopy for organic light-emitting materials
Organic light-emitting materials are widely used in optoelectronics and bioimaging, but sometimes conventional fluorescence spectroscopy techniques can be limited by scattering, background fluorescence, photon pile-up and photobleaching. We report a quantum-spectroscopic approach using frequency-entangled, nondegenerate photon pairs generated via spontaneous parametric down-conversion with heralded detection, to perform photoluminescence lifetime measurements at low excitation intensities. We demonstrate this approach across three organic light-emitting material classes: the fluorescent dye Rhodamine 6G, an organic semiconducting conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), and a fluorescent protein mOrange. The intrinsic timing correlation between signal and idler photons enables coincidence gating that suppresses uncorrelated background counts. Across all materials and integration times of 500, 1000 and 3600 seconds, heralded detection yields signal-to-noise ratios 1.6-3.0 times higher than classical pulsed-laser excitation attenuated to match heralded photon counts in the fitting range. For MEH-PPV, this roughly halves the noise amplitude. Our measured lifetimes closely match long-integration classical pulsed-laser reference values.