| Recently,Carbon quantum dots（CQDs）have become a hot topic of luminescent materials owing to their advantages such as good optical stability,biocompatibility,and low toxicity.CQDs can be combined with other materials to extend their applications.Various composites based on CQDs with multi functions have been a novel field in nano science.These composites have been widely used in many fields such as optoelectronic device,photocatalysts,solar cells,and information storage.They are especially important in the developments of light emitting devices and novel displays.When used in luminescent materials and devices,CQDs are often dispersed in polymer matrices to fabricate flexible thin films.However,a great portion of the emitted light from CQDs is reflected by total internal reflection at the film surface and dissipated through processes such as wave guided modes.Therefore,reducing total internal reflection and increasing the light extraction are of great importance to the application of CQDs in luminescent devices.Besides,when CQDs and other luminescent materials are simultaneously resolved in a solvent,their optical processes will be affected by each other.For instance,the fluorescence spectrum of mixed solution is not simply the sum of respective spectra.The spectrum is affected by processes such as inner filter effects.In order to extend the applications of composites based on CQDs,it is important to investigate the photoluminescence（PL）of mixture containing CQDs.Aiming at the above scientific problems,the following investigations have been carried out in this thesis.（1）SiO2 microspheres were randomly dispersed on the film surface to destroy the total internal reflection,so that the light extraction of CQDs/polymer films was enhanced. CQDs with good PL properties were dispersed in the Poly（vinyl alcohol）（PVA） matrix to make luminescent films.Si O2 microspheres were dispersed on the film surfaces to couple out the total internal reflection.The fabricated films were characterized with absorption spectrum,fluorescence spectrum,and scanning electron microscopy.The PL enhancements with different sphere densities and diameters were observed with a home made microscope equipped with a highly sensitive spectrometer.It was observed that the fluorescence intensities increased with increasing sphere densities,and the PL enhancement increased at first then decreased with increasing sphere diameters.The PL enhancement was as high as 1.83 when the film surface was completely covered by microspheres with the diameter of 0.86μm.It was also verified that the light extraction originated from rather the scattering of individual spheres than diffraction of ordered arrays.The near field optical intensities were numerically calculated with a 2-D Finite Difference Time Domain.（2）PL spectra of mixed solutions containing CQDs and a kind of organic dye molecules （TDBC）have been investigated.At first,absorption and fluorescence spectra of CQDs and TDBC molecules were measured respectively.Then PL spectra of mixtures of CQDs and TDBC molecules were investigated at different relative concentrations.By examining the PL properties,the phenomena of fluorescence quenching were observed.In the broad band PL spectrum of CQDs,dips corresponding to the absorption of TDBC molecules were observed.At a fixed concentration of CQDs,the fluorescence quenching increased with increasing concentration of TDBC molecules. |
