The Study On Multicolor Emission And Energy Transfer Mechanism Of Aluminate-based Phosphors

White light-emitting diodes(WLEDs)has attracted extensive attention and been considered to be the fourth-generation lighting source due to its high efficiency,durability,low energy consumption,and wide applicability.Nowadays,the mainstream strategy to fabricated WLEDs is called phosphor conversion white light-emitting diodes(pc-WLEDs),which uses a blue In Ga N chip to excite yellow YAG:Ce³⁺phosphors.However,it faces the problems of high color temperature and low color rendering index due to the lack of cyan and red light components,which restricts their applications in more colorful usages.Otherwise,there are excessive blue components in its spectrum,which can easily cause irreversible damage to the human eyes,especially for children.In view of this,people have proposed the construction of near-ultraviolet chips with single-phase white light-emitting phosphor or red/green/blue tricolor phosphors for better illumination experience.Above all,as a core component of white LED devices,phosphors directly determine the illumination effect of WLEDs devices.Blue phosphor is one of the hotspots of phosphors used for WLEDs.On the one hand,it can be excited by commercial near-ultraviolet LEDs to emit blue light,which can mix with green light and red light into white light.On the other hand,the luminescent center can transfer part or even all of its energy to other activators to achieve multicolor emission,which can effectively control the luminescence characteristics of this phosphor system.Therefore,the purpose of this work is to improve the luminescence characteristics of Ca₃Al₂O₆ phosphor system,so that they can not only become efficient blue phosphors used for WLEDs,but also achieve multicolor emission through the energy transfer between rare earth ions and hence obtain white or near-white light emission.Here,we systematically study the synthesis,photoluminescence properties and crystal structure of Ca₃Al₂O₆ phosphor system as well as the relationships between them.The Ce³⁺doped Ca₃Al₂O₆phosphors were first prepared by the sol-gel method,and their emission were further tuned through energy transfer and substituting the cations in host matrix.Furthermore,the energy transfer mechanism between Ce³⁺and Dy³⁺and the effect of cations substitution on the emission were discussed in detail.The main work and conclusions can be summarized as follows:(1)This paper first developed a facile sol-gel method to prepare Ca₃Al₂O₆ phosphors,and systematically investigated the crystalline properties,microscopic morphology of as-prepared Ca₃Al₂O₆phosphors.It was found that pure Ca₃Al₂O₆ phase can be synthesized at low temperature(1000?)for merely 2 h;(2)The spectral characteristics of as-prepared Ca₃Al₂O_6:Ce³⁺phosphors were investigated.Given the crystal structure of Ca₃Al₂O₆,the occupancy and multicolor emission of Ce³⁺in the Ca₃Al₂O₆ host with increasing Ce³⁺content were studied in detail.It was found that the as-prepared Ca₃Al₂O₆:Ce³⁺phosphors have intense blue light emission even at low Ce³⁺doping content,which can improve efficiency of energy transfer;(3)Ca₃Al₂O₆:Ce³⁺,Dy³⁺phosphors were synthesized,and the reduction of fluorescence lifetime and spectroscopic analysis revealed that the energy transfer between Ce³⁺and Dy³⁺is dominated by the electric dipole-electric dipole interaction.The color coordinates can be adjusted continuously from the blue region(0.1558,0.0478)to the bluish-white region(0.2241,0.1706)by changing the amount of Dy³⁺,indicating that Ca₃Al₂O₆:Ce³⁺,Dy³⁺phosphors possess certain commercial value;(4)The effect of cationic substitution on the photoluminescence properties of Ca₃Al₂O₆:Ce³⁺phosphors were studied.The cations in the Ca₃Al₂O₆ matrix were partially replaced by Sr²⁺,Ga³⁺,and B³⁺,respectively.The introduction of Sr²⁺and B³⁺increased significantly the emission intensity of the phosphors,and the maximum intensity are increased by 186%and 215%,respectively.The introduction of Ga³⁺tends to leads to the reduction of the emission intensity.At the same time,the emission peak of Ce³⁺was blue-shifted by substituting Ca²⁺by Sr²⁺while red-shifted by substituting Al³⁺by Ga³⁺.