Spontaneous Emission Enhancement by a Rectangular-Aperture Optical Nanoantenna: An Intuitive Semi-Analytical Model of Surface Plasmon Polaritons

The spontaneous-emission enhancement effect of a single metallic rectangular-aperture optical nanoantenna on a SiO2 substrate was investigated theoretically. By considering the excitation and multiple scattering of surface plasmon polaritons (SPPs) in the aperture, an intuitive and comprehensive SPP model was established. The model can comprehensively predict the total spontaneous emission rate, the radiative emission rate and the angular distribution of the far-field emission of a point source in the aperture. Two phase-matching conditions are derived from the model for predicting the resonance and show that the spontaneous-emission enhancement by the antenna comes from the Fabry–Perot resonance of the SPP in the aperture. In addition, when scanning the position of the point source and the aperture length, the SPP model does not need to repeatedly solve the Maxwell’s equations, which shows a superior computational efficiency compared to the full-wave numerical method.

Potassium-Induced Emission Enhancement of Bovine Serum Albumin-Stabilized Red-Emitting Au Nanoclusters: Mechanism and Application to Blood Plasma

Aggregation-induced emission (AIE) enhancement is attractive for bioimaging as it offers higher quantum yields (QYs) from fluorophores via modulation of their immediate environment. Fluorophores with high QYs are essential probes for investigating the spatiotemporal distribution of physiologically important metal ions such sodium and potassium. Potassium ions are vital for normal function of living organisms. The research reported here evaluates the emission intensity of the bovine serum albumin-stabilized red-emitting gold nanoclusters (BSA-rAuNCs) upon uptake of K+. The integrated sphere method was used to determine the absolute QYs and a custom-built fluorescence setup recorded the emission spectra of BSA-rAuNCs. Enhancement of emission intensity was observed upon increasing K+ concentration, within the physiological concentration range of 0 - 150 mM. The emission enhancement was correlated with the particle size and charge analysis. Aggregation of BSA-rAuNCs was found to be responsible for the observed emission enhancement. The QY of BSA-rAuNCs in bovine blood plasma was found to be four times lower than corresponding QY in water.

Environment-sensitive emission of anionic hydrogen-bonded urea-derivative–acetate-ion complexes and their aggregation-induced emission enhancement

Anions often quench fluorescence (FL). However, strong ionic hydrogen bonding between fluorescent dyes and anion molecules has the potential to control the electronic state of FL dyes, creating new functions via non-covalent interactions. Here, we propose an approach, utilising ionic hydrogen bonding between urea groups and anions, to control the electronic states of fluorophores and develop an aggregation-induced emission enhancement (AIEE) system. The AIEE ionic hydrogen-bonded complex (IHBC) formed between 1,8-diphenylnaphthalene (p-2Urea), with aryl urea groups at the para-positions on the peri-phenyl rings, and acetate ions exhibits high environmental sensitivities in solution phases, and the FL quantum yield (QY) in ion-pair assemblies of the IHBC and tetrabutylammonium cations is more than five times higher than that of the IHBC in solution. Our versatile and simple approach for the design of AIEE dye facilitates the future development of environment-sensitive probes and solid-state emitting materials.

Synthesis and Spectroscopic Characteristics of Ligands Based on Quinolin-8-Ol as Useful Precursors for Alq3 Type Complexes

In order to develop reliable methods for the synthesis of various 5-substituted-8-oxyquinoline derivatives for the preparation of Alq3-type complexes, we have improved the reaction conditions on some syntheses described in the literature, successfully synthesized new ligands based on quinolin-8-ol and characterized their chemical structures by NMR. Some of the synthesized quinolin-8-ol derivatives containing incorporated bulky triphenyl or tert-butyl groups showed blue luminescence in the solid state due to the possible aggregation induced emission enhancement (AIEE) with a maximum wavelength around 510 nm. More detailed light-emission property investigation of the mentioned bulky group containing compounds is currently underway.