Preparation And Luminescent Properties Of Red Fluorescent Materials For Warm White LED

White light-emitting diodes(LEDs)have become the main light source in daily life and work owing to their merits of environmental friendliness,high brightness,high stability,long operating times,small sizes,and low power consumption.However,the white LEDs composed of a blue LED chip and yellow-emitting Y₃Al₅O₁₂:Ce³⁺phosphors suffer from high color temperature and poor color rendering index due to the insufficient contribution of red light,which are not suited for indoor lighting.The soft warm-white LEDs similar to the incandescent lamp are more suitable for indoor lightings such as in houses and restaurants.To obtain warm-white LEDs with high brightness and high luminous efficiency,it is urged to prepare low-cost red luminescent materials with high efficiency,high stability,and narrowband emission.In this paper,we systematically investigated the preparation and luminescent properties of red luminescent materials which are divided into rare-earth-doped molybdate and organic-inorganic hybrid perovskite quantum dots as follows:(1)The phosphors prepared by the traditional high-temperature solid-phase method usually suffer from uneven particle size distribution and agglomeration which are harmful to the LED packaging.Here,we prepared the red SrMoO₄:Pr³⁺phosphors with uniform particle size distribution,superior dispersion,uniform morphology and high color purity via the polymer-assisted hydrothermal method.The main emission peak of the red phosphors is located at 647 nm.We systematically study the self-assembly process of the particle,revealing that the ethylene diamine tetraacetic acid(EDTA)and polyetherimide(PEI)in metal precursors can effectively bind the metal ions for guaranteeing the desired homodisperse of metal ions and control the nucleation and self-assembly of phosphor particles.Therefore,the morphology and size of phosphor particles can be precisely controlled.(2)Compared with traditional phosphor materials,the luminescent films exhibit higher uniformity,better adhesion,superior thermal conductivity and higher resolution,however,it is difficult to regulate the thickness and doping ion content.Here,quartz substrate supported red-emitting SrMoO₄:Pr³⁺films are successfully fabricated via a facile polymer-assisted deposition(PAD)method.This method realizes the precise control of the doping ion concentration and film thickness,as well as suppresses the film cracking caused by different expansion coefficients during the heat treatment process.The prepared SrMoO₄:Pr³⁺films show good uniformity,high coverage and good monochromaticity.The photoluminescence quantum yield of the film reaches up to 86%by optimizing the number of spin-coated layers and doping concentrations.(3)To eliminate the mismatch between the substrate and luminescent film,we propose a grain orientation engineering strategy to fabricate textured BaMoO₄:Eu³⁺thin films by a simple and low-cost polymer-assisted deposition method.We systematically studied the effect of texture on the crystal structure,microscopic morphology,and luminescent properties of the film.It is showed that the differently-orientated films on substrates show different properties due to the lattice mismatch.It is verified that the BaMoO₄:Eu³⁺film deposited on the(001)-oriented Si substrate presents the higher luminescence performance and preferred orientation with a Lotgering factor as high as 94.6%.(4)To enhance the air stability of organic-inorganic hybrid MAPbI₃ perovskite quantum dots,we proposed a combination stratagem of solvent engineering and ligand engineering to improve the stability by simultaneously reducing internal-external defects.The dose-reduced coordinated solvent can effectively eliminate the internal iodine vacancies and external residual solvent molecules.Using short-chain amine ligand can effectively repair the external surface defects of perovskite QDs,and the formed compact hydrophobic protective layer can effectively resist the invasion of moisture.The air stability of the MAPbI₃ perovskite quantum dots is improved by several orders of magnitude,and the quantum yield is as high as 80%.At the same time,this method could be extended to prepare a series of color-tunable MAPbX₃(X=Cl,Br.I)QDs.(5)To further improve the stability of perovskite quantum dots,the short-branched isoamylamine is employed as the amine-based ligand.The great steric hindrance of branched isoamylamine efficiently prevents the agglomeration of contiguous adjacent MAPbI₃ quantum dots.Moreover,the branch of isoamylamine assemble a dense hydrophobic protective layer on the perovskite surface,which effectively slow down the rate of degradation.The proposed strategy significantly enhances the air stability,UV stability,and thermal stability of the MAPbI₃ QDs.At last,the MAPbBr₃ quantum dots are used to fabricate the electroluminescent perovskite LEDs,and the external quantum efficiency is as high as 6.89%.