Preparation And Luminescence Properties Of Sr₃Y₂（BO₃）₄ Phosphor Doped With Rare Earth

As science and technology continue to advance,the demand for high-quality illumination sources is increasingly significant.White Light Emitting Diodes（LEDs）that feature low energy consumption,long lifetime,short response time,excellent color rendering,and environmental friendliness are gradually becoming a hot research topic.Mainstream white LEDs are achieved through a phosphor conversion process,and the quality of the phosphor determines the quality of the LED device.Thus,the development of phosphors with high luminous efficiency and thermal stability is crucial.This paper synthesizes a series of blue,green,and orange-red phosphors doped with rare-earth ions in a borate matrix Sr₃Y₂（BO₃）₄using a high-temperature solid-phase method,studying the crystal phase,luminescent properties,and thermal stability of the samples.The specifics are as follows:1.A novel blue Sr₃Y_（2-x）（BO₃）₄:x Ce³⁺phosphors were prepared were synthesized by high-temperature solid-phase method under a reducing atmosphere.Its crystal phase and luminescent properties were studied.Excited at 339 nm,this phosphor shows an emission peak around 416 nm.The optimal doping concentration of Ce³⁺ions is x=0.02.It was found that when the temperature reaches 423 K,the luminous intensity of the Sr₃Y_1.98（BO₃）₄:0.02Ce³⁺phosphor is 59.9%of that at room temperature.A white LED was made by combining Sr₃Y_1.98（BO₃）₄:0.02Ce³⁺blue phosphor with commercial red and green phosphors and a 365 nm chip.The white LED has color coordinates of（0.35,0.39）,a color temperature of 4873 K,and a color rendering index of 86.3.Therefore,Sr₃Y₂（BO₃）₄:Ce³⁺is a potential blue phosphor for white light LEDs.2.A series of green Sr₃Y_（2-y）（BO₃）₄:y Tb³⁺phosphors were synthesized using the high-temperature solid-phase method by firing in a carbon monoxide atmosphere.Their crystal phase and luminescent properties were studied.Excited at 245 nm,this phosphor has emission peaks at 490 nm（⁵D₄→⁷F₆）,545 nm^{（5）D₄→7F₅},585 nm（⁵D₄→⁷F₄）,and624 nm（⁵D₄→⁷F₃）.The optimal doping concentration of Tb³⁺ions is y=1.0.The concentration quenching mechanism of the phosphor is due to the energy transfer of electric dipole-dipole interactions.The Sr₃Y_（2-y）（BO₃）₄:y Tb³⁺phosphor has good thermal stability.At 423 K,the luminous intensity of the phosphor can reach 1.076times that at room temperature.A white LED was made using Sr₃Y（BO₃）₄:1.0Tb³⁺green phosphor.The LED device has a lower color temperature（4278 K）,a higher color rendering index（88.4）,and corresponding color coordinates（0.37,0.36）.This demonstrates that our sample,Sr₃Y₂（BO₃）₄:Tb³⁺,is a green phosphor with good thermal stability for use in white light LEDs.3.A series of orange-red Sr₃Y_（2-x）（BO₃）₄:x Sm³⁺phosphors were synthesized using the high-temperature solid-phase method.The crystal phase and luminescent properties of the Sr₃Y_（2-x）（BO₃）₄:x Sm³⁺phosphors were studied.The excitation spectrum of the phosphor consists of a broad band peak located in the UV region and sharp peaks in the near UV and visible light region.The broad band peak results from the charge transfer band transition of O^2-→Sm³⁺;the sharp peaks result from the f-f transition absorption of Sm³⁺.Under 403 nm excitation,the emission spectrum of Sr₃Y_（2-x）（BO₃）₄:x Sm³⁺shows two weaker emission peaks(⁴G_5/2→⁶H_5/2,566 nm;⁴G_5/2→⁶H_9/2,649 nm)and one stronger emission peak(⁴G_5/2→⁶H_7/2,601 nm).The optimal concentration of Sm³⁺in Sr₃Y₂（BO₃）₄matrix is x=0.04.The main cause for concentration quenching is the electric dipole-dipole interaction.The color coordinates of Sr₃Y_（2-x）（BO₃）₄:x Sm³⁺are similar,indicating that the color of the phosphor is stable.Overall,Sr₃Y₂（BO₃）₄:Sm³⁺is a novel orange-red phosphor suitable for excitation from UV to visible light.4.A series of green Sr₃Y_（1.91-y）（BO₃）₄:0.09Ce³⁺,y Tb³⁺phosphors were synthesized using the high-temperature solid-phase method in a reducing atmosphere.The luminescent properties of Sr₃Y_（1.91-y）（BO₃）₄:0.09Ce³⁺,y Tb³⁺were studied.An energy transfer process exists between Ce³⁺ions and Tb³⁺ions.According to Dexter’s theory and Reisfeld’s theory,the energy transfer mechanism was determined to be electric quadrupole-quadrupole interactions.By changing the doping concentrations of Ce³⁺ions and Tb³⁺ions,the color of the emitted light can be adjusted in the Sr₃Y₂（BO₃）₄matrix.At 433 K,the luminous intensity of the Sr₃Y_0.71（BO₃）₄:0.09Ce³⁺,1.2Tb³⁺phosphor can reach 1.008 times that at room temperature.A white LED was made using the Sr₃Y_0.71（BO₃）₄:0.09Ce³⁺,1.2Tb³⁺phosphor.The resulting LED has a lower color temperature（4581 K）and a higher color rendering index（91.0）,with relevant color coordinates of（0.36,0.35）.These results prove that Sr₃Y₂（BO₃）₄:Ce³⁺,Tb³⁺is a thermally stable phosphor with adjustable luminescent colors for near UV white light LEDs.5.A series of green phosphors partially replacing Sr₃Y_0.71（BO₃）₄:0.09Ce³⁺,1.2Tb³⁺with Ba²⁺ions were successfully synthesized by the high-temperature solid-phase method.Their crystal phase and fluorescence spectra were studied.The results prove that a proper concentration of Ba²⁺ions partially replacing Sr²⁺ions in the matrix can enhance the luminescent intensity of the Sr₃Y_0.71（BO₃）₄:0.09Ce³⁺,1.2Tb³⁺phosphor.