Study On Preparation,Properties And Application Of Bismuth And Europium Doped Inorganic Luminescent Materials

Illumination and display are important requirements for improving the development of urban civilization,and many development processes cannot be separated from illumination and display.White light emitting diodes（WLEDs）have attracted widespread attention in the illumination and display fields due to their high energy efficiency,long life,low power consumption,fast response and environmental protection.In the field of illumination,traditional lighting is gradually being replaced by more advantageous WLEDs.There are two ways to implement WLEDs.One is the combination of blue LED chip with one（yellow）or two（green and red emitting,respectively）phosphors to form white light.Another is to use near-ultraviolet LED chip to excite red,green,and blue phosphors combine to produce white light.At present,WLEDs are not effective due to factors such as the low luminous efficiency of existing red phosphors or the incomplete spectrum of the three primary color phosphors.Therefore,the research of new high-efficiency and stable phosphors as lighting equipment is the focus of current research.In the display field,LCDs are"never slaves".Because LCDs have great advantages over OLEDs in terms of performance,price,and lifetime,and WLEDs are a new type of backlight unit in modern LCD applications.The WLEDs used in backlight display need a wide color gamut and high luminous efficiency.Therefore,the current research hotspot is to find phosphors with wide excitation,narrow emission,high quantum efficiency,and excellent thermal stability.Mg₃Y₂Ge₃O₁₂ belongs to the garnet structure,and it has a highly symmetrical structure.Not only the entire unit cell is symmetrical,but the polyhedron formed by the corresponding atoms and oxygen atoms is also symmetrical.Therefore,it is suitable for doping rare earth ions or transition metal ions such as bismuth ions and europium ions.Rb Na（Li₃Si O₄）₂ belongs to the UCr₄C₄ structure.It is a highly cohesive rigid frame structure with cubic sites of divalent europium ions(Eu²⁺).Therefore,this structure is conducive to doping Eu²⁺for research.The research progress is as follows:1.Mg₃Y₂Ge₃O₁₂:Eu³⁺,Mg₃Y₂Ge₃O₁₂:Bi³⁺and Mg₃Y₂Ge₃O₁₂:Eu³⁺,Bi³⁺samples were synthesized by high-temperature solid-phase method.A single-doped Eu³⁺sample can emit red light under the excitation of 290 nm,322 nm and other light,a single-doped Bi³⁺sample can emit invisible ultraviolet light at 322 nm under the 290 nm excitation.But the co-doped sample emits red light under 290 nm excitation and its intensity of the red light emitted is greater than the single-doped Eu³⁺sample,which is due to the energy transfer between Bi³⁺and Eu³⁺.At the same time,the integrated emission intensity of Mg₃Y₂Ge₃O₁₂:Eu³⁺,Bi³⁺samples is also higher than that of commercial red phosphor Y₂O₃:0.05Eu³⁺.Through testing,it was found that the co-doped sample has excellent luminous thermal stability.At 150°C,the integrated emission intensity still has 94.42%of that at room temperature.Therefore,Mg₃Y₂Ge₃O₁₂:Eu³⁺,Bi³⁺phosphors have potential application value in the field of WLEDs illumination.2.A series of samples with Rb Na（Li₃Si O₄）₂ matrix providing Rb ion vacancies and Na ion vacancies were synthesized by high-temperature solid-phase method.The series providing Rb ion vacancies(Rb_1-xNa（Li₃Si O₄）₂:x Eu²⁺):Rb_0.9Na（Li₃Si O₄）₂:0.1Eu²⁺has a wide excitation,and can emit blue light（472 nm）and green light（523 nm）under 430 nm excitation.By comparing the experiment and the Van Uitert formula,we can know that blue light is caused by Eu²⁺replacing Rb⁺,and green light is caused by replacing Na⁺.Through the Density Functional Theory calculation of the formation energy,it is concluded that Eu²⁺is more likely to enter the Na⁺site,which is consistent with the information in the spectrum.At the same time,the Rb_0.9Na（Li₃Si O₄）₂:0.1Eu²⁺sample has a quantum efficiency of 62.9%,and its luminous thermal stability is good.The integrated emission intensity at 150°C still has 81.9%of that at room temperature.The spectrum of warm WLEDs packaged with a 430 nm blue chip and commercial dark red powder Ca Al Si N₃:Eu²⁺almost covers the entire visible light region,which has a high color rendering index（CRI,Ra=88.9）and a suitable correlated color temperature（CCT）=3714 K).Therefore,Rb_0.9Na（Li₃Si O₄）₂:0.1Eu²⁺phosphor has great potential in the field of WLEDs illumination.The series providing Na ion vacancies(Rb Na_1-y（Li₃Si O₄）₂:y Eu²⁺):Rb Na_0.9（Li₃Si O₄）₂:0.1Eu²⁺has a wide excitation of 320-500 nm,and it emits narrow-band green light（523 nm）with the full width at half maximum of only 44 nm under the excitation of 460 nm.Its quantum efficiency is 70.5%and its luminous thermal stability is good.At 150°C,the integrated emission intensity still has 83.3%of that at room temperature,and the emission peak intensity at 523 nm is still 74.9%of that at room temperature.At the same time,as the temperature increases,the full width at half maximum of the emission peak still has a narrow state.At 250°C,the full width at half maximum of the emission peak still does not exceed 54 nm.The luminous efficiency of the WLEDs packaged with blue light chip（λ=460 nm）and commercial red phosphor K₂Si F₆:Mn⁴⁺is 105.74 lm/W and the color gamut of the WLEDs is 116.1%NTSC.Therefore,Rb Na_0.9（Li₃Si O₄）₂:0.1Eu²⁺green phosphor has great potential in the field of WLEDs backlight display.