Preparation And Properties Of Novel Color Adjustable Phosphors

With the advent of the 21st century,the new concept of energy saving and environmental protection has become the first goal of development.White LEDs have become the darling of the new generation of lighting devices due to their non-polluting,long life,fast response,high luminous efficiency,and recyclability.At present,the main commercial white LEDs lack the red component of white light,resulting in high color temperature(CCT,Tc>4500),low color rendering index(CRI,Ra<90)and low energy efficiency.Therefore,synthesizing an efficient and stable red light tunable phosphor is the key to solving the problem.Borate phosphors are favored by scientists for their simple preparation process,easy industrialization,stable chemical and physical properties,high luminous efficiency,and stable matrix.This article mainly focuses on borate as the research object,and phosphate as the extended research direction.The Ca4LaO(BO3)3,Ca3Y2B4O12 and Na3Y(PO4)2-based phosphors were synthesized by high-temperature solid-phase method.The phase composition,morphology,performance,energy transfer and luminescence of the phosphors were analyzed by XRD,SEM,and fluorescence spectroscopy.The main research results are as follows:(1)A new type of color-adjustable white light-emitting phosphor Ca4LaO(BO3)3:Dy3+,Eu3+was synthesized by high-temperature solid-phase method.Ca4LaO(BO3)3:Dy3+has the best emission effect when the excitation wavelength is 348 nm,the best doping concentration is 0.04 mol.Under 348 nm excitation,the emission peaks are located at 491 nm,587 nm and 613 nm,respectively.With the increase of Eu3+ concentration,the intensity and lifetime of Dy3+ continue to decrease,The increase of Eu3+ emission intensity.After calculation,it is found that the main way of energy transfer in phosphor is electric dipole-electric dipole interaction.With the increase of Eu3+ concentration,the color temperature of Ca4LaO(BO3)3:Dy3+,Eu3+decreases continuously,and the color moves from cold white light to warm white light,and finally to red light.This phenomenon is of great help to the lack of warm white light in the LED market.Therefore,Ca4LaO(BO3)3:Dy3+,Eu3+has a good market application prospect.(2)A series of Ca4Lao(BO3)3 red phosphors were synthesized by high temperature solid phase method.The XRD pattern,luminescence characteristics,fluorescence lifetime,spectral overlap,color coordinates,energy transfer and luminescence principle of phosphors are discussed in detail.The concentration quenching point of Eu3+doped Ca4LaO(BO3)3phosphor at 464 nm excitation is 0.08 mol,and the optimal doping concentration of Sm3+doped Ca4LaO(BO3)3 phosphor is 0.04 mol.Excited at 464 nm,Ca4LaO(BO3)3:Eu3+and Ca4LaO(BO3)3:Sm3+have spectral overlap at 607 nm and 613 nm,and promote the luminescence of each other.With the increase of Sm3+ concentration,the color changed to red first,and then to orange red.When the concentration of Sm3+is 0.04 mol,the emission intensity reaches the best.The CIE coordinates of Ca4LaO(BO3)3:0.08Eu3+,ySm3+fluctuated between(0.54,0.4417)and(0.5779,0.4099)with the change of Sm3+concentration.It is worth mentioning that the phosphor can not only improve the emission intensity of Eu3+through energy transfer,but also enhance the emission intensity of red light again through the spectral overlap in the 613 nm region.Therefore,this kind of phosphor is in line with the current situation of the lack of red light elements in the LED market,and it is a kind of high-efficiency phosphor with wide application prospect.(3)A series of Na₃Y(PO₄)₄:Re3+(Re=Tm,Tb,Eu)phosphors were synthesized by solid phase method.In Tb3+doped Na₃Y(PO₄)₄ phosphors,the optimal doping concentration of Tb3+is 0.5 mol,the optimal excitation peak is located at 375 nm,and the optimal emission peak is located at 547 nm.With the increase of Tb3+doping concentration,the color of Na₃Y(PO₄)₄:Tb3+phosphor(blue?green)changed continuously.It has been confirmed that there is an energy transfer phenomenon between Tb3+and Eu3+ions.With the concentration of Eu3+ reaching 0.09 mol,the transfer efficiency reaches 93.57%.The reason for the energy transfer phenomenon is interaction.Na₃Y(PO₄)₄:xTm3+,yTb3+,zTm3+by appropriately changing the doping concentration of Tb3+,Tm3+and Eu3+,the white emission of the phosphor can be achieved(the green,red,blue and white colors can be adjusted).The fluorescence properties of the prepared materials indicate that Na₃Y(PO₄)₄:Re3+(Re=Tm,Tb,Eu)can be used as white WLED phosphors.(4)Ca3Y2B4O12:Tb3+,Eu3+phosphors were synthesized by high temperature solid phase method.The optimal concentration of Tb3+ single doped phosphor is 0.08 mol,and the optimal emission peak is located at 545 nm.The main reason for concentration quenching is non-radiation transition.In the Tb3+,Eu3+co-doped phosphors,by changing the concentration ratio of Tb3+,Eu3+ can achieve the purpose of color from green to yellow to orange yellow.