Studies On The Orange-red Composite Quantum Dots Ratio Control For Lighting Applications

With the continuous improvement of luminious efficiency of white light emitting diodes(WLEDs),more stringent requirements have been placed on their luminous spectrum and lighting quality.High-performance full-spectrum WLEDs have gradually become the mainstream research direction for lighting applications.To date,WLEDs used for lighting are commonly developed by incorporating broad-emitting green-yellow phosphors and narrow-emitting monochromatic red quantum dots(QDs).These WLEDs present superb spectral continuity in the green and yellow region but some spectral loss in the orange-red region.To tackle the key issue of improving the spectrum in the orange-red region for the full-spectrum WLEDs,which needs to be solved urgently,this paper proposes to use composite orange-red QDs as a technical approach,and systematically study the optical characteristics of orange and red single quantum dot as well as composite quantum dots,aiming to master the laws of self-absorption and fluorescence resonance energy transfer(FRET)between the polychromatic QDs,and to achieve the precise control of the spectrum for the composite QDs,in order to improve the spectral continuity in the orange-red region for the WLEDs and their color quality.The main tasks completed are as follows:1.By layered encapsulation of red quantum dots(R-QDs)with different concentration on three LED chips coated with different color phosphors ratios,it is confirmed that the R-QDs are effective in minimizing lumen loss in the red wavelength region.2.Matlab software was developed to similate the composite quantum dot luminescence spectrum by inputting monochromatic quantum dot luminescence spectrum,which serves the purpose to guide the spectrum design of the composite QDs for WLED applications.3.The optical properties of orange and red single quantum dot silica films at different concentrations were investigated.Since the Stoke’s shift for orange QDs(O-QDs)is larger than R-QDs,R-QDs reach maximum photoluminescence(PL)intensity and quantum efficiency(QE)at 2 mg/m L,while O-QDs at 10 mg/m L.Through the analysis of time-resolved photoluminescence spectroscopy(TRPL),the lifetime of quantum dots showed a trend of rapid increase at first and then slowed down with increasing concentration,further verifying the self-absorption effect of QDs at high concentrations.4.The optical properties and FRET of orange-red composite quantum dots(O-R-QDs)prepared based on the optimal concentration of the above-mentioned monochromatic orange and red quantum dots were studied systematically.The theoretical analysis of the TRPL test results shows that when the acceptor(R-QDs)is introduced,the lifetime of the donor(O-QDs)is reduced and the energy transfer efficiency is improved due to the intervention of the energy transfer channel.Based on this,the optimal ratio of O-QDs to R-QDs for the composite quantum dot mixture was determined.Studies on the effect of composite QDs concentration reveals that as the concentration of the composite quantum dots increases,the FRET efficiency decreases;In the meantime,its lifetime at the emission wavelength of the donor increases as the concentration increases.It indicates that both FRET and self-absorption mechanism coexist,that is,as the concentration increases,the enhanced self-absorption results in the inhibition of FRET efficiency.These results are used to optimize the QE and spectral controllability of the composite-QDs,and fabricate composite quantum dot WLED.Compared with WLEDs made from monochromatic quantum dots,it exhibits better spectral continuity in the orange-red region with a CRI of92.1,which enhances the color rendering quality.