Study On White Light LEDs Based On Aqueous AgInS₂/ZnS Quantum Dots And Carbon Dots

As a promising energy-saving technique,the solid-state white light-emitting diodes(WLEDs)have received considerable attention because of their outstanding merits,like small size,long operational life,and fast response and so forth.However,the down-conversion fluorescent materials used to construct WLEDs are mostly rare-earth phosphors or high toxic quantum dots based on Cd²⁺and Pb²⁺,so the researcher have been seeking for eco-friendly phosphors substitutes for such toxic quantum dots or rare-earth phosphors.Based on this,herein we would mainly focus on how to combine low-cost,and environmentally-friendly Ag In S₂/Zn S(AIS)and carbon dots(CDs)to prepare WLEDs.(1)AIS and CDs were prepared by aqueous solution and solvothermal method,respectively.And their optical properties,composition,and morphology were investigated by TEM and fluorescence PL.Those results indicate that we successfully synthesized the AIS and CDs with uniform distribution,wide fluorescence spectrum,and high fluorescence efficiency,which laid the foundation for the subsequent construction of WLEDs.(2)We studied the high-performance WLEDs devices based on yellow-light emitting AIS and blue-light emitting CDs.At first,AIS quantum dots were coated with SiO₂,which could be used as the carrier for growing CDs at the same time,and then CDs were grown on the surface of silica sphere by electrostatic attraction.As a result,we obtained a core-shell structure nanocomposite(AIS-CDs),which successfully overcome fluorescence quenching of the CDs.In addition,the solid-state white-light emission was achieved by combining blue-light emission of CDs and yellow-light emission of AIS,and the photoluminescence quantum yield(PLQY)can reach 35%.Furthermore,the low-cost and environmentally-friendly nanocomposites were used as down-conversion fluorescent materials on UV chips,and the corresponding WLEDs with a color rendering index(CRI)of 91 were successfully fabricated.The optimized CIE index of the fabricated WLEDs is located at(0.32,0.33),which is close to standard white light(0.33,0.33).Additionally,the luminous efficiency of the as-developed WLEDs can reach 15.1 lm W^-1.(3)We studied the WLEDs with a high color rendering index(CRI)based on blue-and green-emissive CDs,and red-emissive AIS.Firstly,the green-and blue-light emitting CDs powders without fluorescence quenching were prepared by using3-(2-aminoethyl amino)propyl trimethoxy silane as ligand modification and TEOS coating treatment.And then a trichromatic white LED was constructed via combining the non-quenched fluorescent green-and blue-emissive CDs,and red-emissive AIS.By adjusting the ratio of the three materials,we obtained the WLEDs with the color temperature(CCT)adjustable arbitrarily in the range of 3387 to 8018 K,and the color rendering index(CRI)always above 90,up to 97,and a luminous efficiency of 20.3 lm W^-1.In addition,under the operating voltage of 3.0-3.5 V,the prepared WLEDs have good color rendering stability,and the parameters such as CCT and CRI can remain unchanged.To sum up,in this work we prepared high-performance white light LEDs based on AIS and CDs,which could be a new idea for the development of low-cost,and environmentally friendly WLEDs devices.