Preparation And Optical Properties Of YAG:Ce Phosphor Coated With Perovskite Quantum Dots

White light-emitting diodes?WLEDs?have rapidly developed as the fourth-generation lighting sources for their low energy consumption,long life,fast response as well as environmental friendliness.Currently,typical WLED is achieved by InGaN blue chip combined with YAG:Ce yellow-emitting phosphors.However,for lacking of red light,the YAG:Ce-based WLEDs have a low color rendering index and high correlated color temperature.In this paper,to solve the above problems,organic-inorganic hybrid perovskite quantum dots?QDs?were introduced as the red-light component of YAG:Ce-based WLEDs.Instead of conventional randomly mixing the red component powder with yellow phosphor,perovskite QDs were uniformly coated onto the surface of YAG:Ce particles by chemical bonding.The coating process was completed in the QDs colloidal solution which avoided the aggregation of QDs.This study focuses on the synthesis of organic-inorganic hybrid perovskite QDs and the coating of QDs on the surface of YAG:Ce particles.Firstly,the influence of the volume of perovskite precursors and different ammonium derivative ligands on morphology and optical properties of the prepared QDs were systematically investigated.Next,QDs coated on YAG:Ce?QDs@YAG:Ce?was achieved by modifying the surface of YAG:Ce and ligand binding to the surface of MAPbBr_3-xI_x QDs.The effects of amine-functionalization and QDs coating on the optical properties of YAG:Ce phosphors were studied.Finally,WLEDs were fabricated by combining the QDs@YAG:Ce with blue LED chip,and the optical performance of the WLED was tested.Experimental research shows that:?1?During the ligand-assisted re-precipitation synthesis of MAPbBr3 QDs,few crystal nuclei was generated due to lower amount of precursor at lower volume of the perovskite precursor solution,which was favorable for the growth of large perovskite crystals.At the higher volume of the perovskite precursor solution,the inhibition of crystal growth with increased amount of precursor was compensated by increasing the polarity of mixture solvent,which led to the dissolution of surface ligands and eventually growth of large perovskite crystals.Therefore,among the 0.1,1,and 2samples,MAPbBr3 QDs prepared by using 0.5 mL of precursor solution possess excellent optical properties and stability.?2?During the synthesis of QDs,different ammonium derivative ligands have different binding modes with the surface of the QDs,which consequently affects the optical properties of the QDs.Compared to amine ligand,the ammonium salt could coordinate to both surface cations and anions of QDs to passivate their surface defects more effectively,leading to enhanced optical properties.Moreover,the combination of oleic acid with amine rather than ammonium salt ligand,could trigger the protonation-deprotonation reaction to further improve their coordination effect on QDs surface,thus leading to significantly enhanced optical properties of QDs.?3?MAPbBr_0.5I_2.5.5 red QDs was chosen as red-light component for its high PLQY by studying the luminescent properties of MAPbBr3-x Ix QDs with different I content?x=0.5-3?.Then,the MAPbBr_0.5I_2.5.5 QDs were attached to the functionalized YAG:Ce particles to obtain QDs@YAG:Ce particles which realized simultaneous emission of yellow and red light.In addition,a white LED was fabricated based on QDs@YAG:Ce and a blue LED chip.The color rendering index and correlated color temperature of WLEDs have been improved.In addition,by changing the volume of the QDs colloid solution during the synthesis of QDs@YAG:Ce,both electroluminescence spectrum and luminous efficiency of the prepared WLEDs can be adjusted.