Studies On The Preparation And Luminescent Properties Of The Borate Red Phosphors Based On The VUV LED Chips

With the development of economy and the consumption of energy，developingnew energy-saving products has become a focus of people’s research. White LED isconsidered to be the fourth generation of lighting tool and is widely favored by peoplefor its high photosynthetic efficiency, low energy consumption, low pollution and soon. Presently the method of generating white-light-emitting diodes is usuallycombining a blue light emitting chip with a yellow emitting phosphor. However, thecolor temperature of this kind of white LEDs is not easy to control. And due toabsence of a long-wavelength red component in the visible spectrum, this kind ofwhite LEDs shows relatively low color rendering index, which leads to emit coldwhite light and limits its popularization. Thanks to significant research progress onUV-LEDs, above-mentioned problem might be solved by fabricating white LEDs witha near ultraviolet (NUV) chip plus blue-, green-and red-(RGB) tricolor phosphors.Therefore, it is an urgent task to search for efficient LED phosphors excited by NUVnowadays. In this paper, we try to find some borate red phosphors, which can beexcited by near ultraviolet LED, and improve their luminescent properties.Firstly, red phosphors Ba2Mg(BO3)2: Eu2+, Mn2+, M2+(M=Sr, Ca and Zn) areprepared by a high temperature solid-state reaction method. The phosphors exhibit redemission bands centered at622nm and have broad excitation bands extending from250to450nm with a maximum at365nm, which makes them potential redphosphors for near-ultraviolet light-emitting diodes-based solid-state lighting. Thesubstitution effect of doped Sr2+, Ca2+and Zn2+ions on luminescence properties inBa2Mg(BO3)2host has been systemically investigated. It is found that the doped Ca2+and Zn2+ions effectively enhance the luminescence intensity, while Sr2+lowers theluminescent intensity. Especially, the intensity of the phosphor has been enhanced by60%with3mol%of Zn2+doped. It is believed that the change of Mg2+sites ratherthan Ba2+in Ba2Mg(BO3)2host has more significant impact on the luminescenceproperties and is more possible to enhance the light emission intensity.Secondly, Eu3+, Sm3+doped separately and co-doped LiY6O5(BO3)3phosphorsare prepared by a high temperature solid-state reaction method. The phosphors emitbright red light under NUV light, which are suitable to be used for near-ultravioletlight-emitting diodes-based solid-state lighting. The influence of Li+concentration onthe composition of the phosphor crystal structure and the luminescent properties of the synthesized phosphors are also systemically investigated. It is seen that excessLiCO3can promote the synthesis of LiY6O5(BO3)3, best when Li+excess200%.When Eu3+, Sm3+doped separately, the luminescent intensity enhances with theconcentration of Eu3+, Sm3+increase. And that reaches the highest intensity when thedoping concentration of Eu3+, Sm3+increases to30mol%and1mol%, respectively.When Eu3+, Sm3+co-doped, the luminescent intensity decreases with theconcentration of Sm3+increase, which is seen that under395nm excited, the doped ofSm3+can’t improve the luminescence properties of LiY6O5(BO3)3: Eu3+. Under406nm excited, the energy transfer from Sm3+to Eu3+is found in LiY6O5(BO3)3: Eu3+,Sm3+phosphors. The energy transfer mechanism between Eu3+and Sm3+is studied.