Bloch surface wave-coupled emission from quantum dots by ensemble and single molecule spectroscopy

Abstract

We report the spectral properties and spatial distribution of quantum dot (QD₅₇₅) emission on a one-dimensional photonic crystal (1DPC). Our 1DPC substrate consists of multiple layers of dielectrics with a photonic band gap (PBG) near the QD₅₇₅ emission maximum. The 1DPC was designed to display a surface-trapped electromagnetic state known as a Bloch surface wave (BSW) at the 1DPC–air (sample) interface. Ensemble angle-dependent emission intensities revealed a sharp angular emission peak near 41° from the normal which is consistent with the BSW resonance at 575 nm. We further examined the emission from single QDs on the 1DPC. A notable increase in fluorescence intensity from QD₅₇₅ particles was observed on the BSW substrate compared to the glass substrate from the scanning confocal fluorescence images and from the intensity–time trajectories of single QD₅₇₅ particles. The intensity-decays showed substantially faster decay (4-fold decrease in emission lifetime) from the single QD₅₇₅ particles on the 1DPC substrate (∼4.8 ns) as compared to the glass substrate (∼18 ns). We observed the spectral characteristics of the individual QD₅₇₅ particles on 1DPC and glass substrates, by recording the single particle emission spectra through the 1DPC. The emission spectra of the single QD₅₇₅ particles are similar (with emission maxima around 575 nm) on both substrates except for a substantial increase in intensity (about 10-fold) on the BSW substrate. Our results demonstrate that quantum dots can interact with Bloch Surface Waves (BSW) on a 1DPC. To the best of our knowledge, this is the first report on the single particle fluorescence studies on a 1DPC substrate. The ∼10-fold increase in total intensity in combination with 4-fold reduction in emission lifetime suggest 1DPCs with BSW modes have potential use in sensing and single molecule spectroscopy.