Enhancement Upconversion Fluorescence And Its Detection Application Of Composite Photonic Crystal

Lanthanide–doped upconversion nanoparticles(UCNPs)are widely used in applications such as bioimaging,photodynamic therapy,solar cells,optical sensing and micro lasers due to their excellent advantages.However,the high–performance applications of UCNPs are limited due to their inherent low quantum yields.There are three main methods for enhancing fluorescence: optimized synthesis,photonic crystals,and plasma enhancement.Optimized synthesis includes many methods to improve the properties of UCNPs by changing the synthesis strategy,such as adjusting the lattice,core–shell structure and doping ions.Photonic crystals modulate the intensity and other properties of incident excitation light and emitted fluorescence by reflection,focusing and localization.In this paper,we focus on the optical field modulation and fluorescence enhancement of 2D(monolayer)photonic crystals.We have studied the fluorescence enhancement of 2D photonic crystal as follows:(1)We investigated the fabrication of 2D photonic crystals using a gas–liquid interface self–assembly method to fabricate 2D photonic crystal arrays.Three types of 2D photonic crystals on glass substrates of 500,1μm and 2μm polystyrene microspheres have been fabricated.The morphology of the monolayer array structures was characterized by the optical microscopy and scanning electron microscope(SEM).(2)The structural color and fluorescence enhancement mechanism of the photonic crystals were studied.Monochromatic photographs were taken at different angles with white light incidence,and the angular range varying from red to violet is called the viewable angle.The viewable angle of structural color for 500,1μm and 2μm photonic crystal arrays were 45°,18° and 9°,respectively.The effect of different sizes of microsphere light field localization was experimented and simulated by FDTD.It is found that the strongest fluorescence enhancement of the 1μm structure is due to the formation of a strong 980 nm localized light field on the upper surface.Finally,we designed visible–near–infrared dual–mode labels combining the structural color and fluorescence enhancement effects of photonic crystals.(3)The composite photonic crystal array structure was used for concentration of acetic acid.We measured the fluorescence intensity of the composite structures at different acetic acid concentrations and found a linear relationship between acetic acid concentration and fluorescence intensity.We also investigated the green–to–red and green–to–blue ratios of photonic crystal–UCNPs fluorescence at different concentrations of acetic acid,and demonstrated the whispering corridor effect on the burst of fluorescence at low power.(4)The composite photonic crystal structure was also used for temperature sensing.Four composite structures,UCNPs,photonic crystal@UCNPs,PC@UCNPs@Au nanoparticles and PC@Au film@UCNPs,were designed.These four composite structures have been measured the fluorescence intensity,temperature sensitivity,signal–to–noise ratio and sample temperature change under different situations by changing the power,structure,concentration,and angle.The phenomena and mechanism light location and fluorescence enhancement of photonic crystal and plasma were investigated.