Preparation And Research On Luminescent Properties Of Vanadate And Tungstate Phosphors

Low-consumption light sources attract more and more attention in the long lifespan,high efficiency,low energy consumption,energy saving and environmental friendliness.White light-emitting diodes(w-LEDs)are a new generation of green light source which have been expected to replace traditional lighting.The commercial w-LEDs can be made combining an In Ga N-based blue LED chip with a yellow phosphor(YAG:Ce3+)to get the yellow light and then mixed with unabsorbed blue light to generate white light.The lack of red light makes the color rendering index lower.We also couple a near-ultraviolet LED chip with tricolor(red,green,and blue)phosphors and then three colors of light mix to bring out white light.This method need to make a big breakthrough because of the low luminous efficiency of the existing red phosphors.Therefore,the studies of new red phosphors are the focus of current research.Vanadate is an excellent optical material with high stability,good crystallinity and high visible light transparency.It is also one kind of typical matrix sensitizer material.The[VO4]3-group in the vanadate crystal lattice is called as a high-efficiency luminescence center,which can absorb the ultraviolet light energy and convert it into visible light or the rare earth ions in the way of radiative transition,and enhance the rare earth luminous efficiency.Tungstate,as an optical material,has excellent thermal stability and chemical stability.As one type of host material it has a wide excitation and emission spectrum and can be well matched with near-UV LED chip and blue LED chip.This kind of wide emission spectra are beneficial to the adjustment of emission color.In this paper,a series of new Ba2 La V3O11:Eu3+ and Ba6Gd2W3O18:Eu3+ red phosphors were synthesized by the traditional solid-state reaction method.The luminescence properties of the obtained phosphors are characterized by the XRD,SEM and luminescence spectra.The following research progresses have been achieved:1)Ba2La V3O11:Eu3+ phosphor was firstly synthesized using the traditional high-temperature solid-state reaction method.Their luminescence properties were studied byphotoluminescence excitation and emission spectra.The excitation spectrum shows a broad band at the 200-370 nm region in the center of 275 nm due to the overlap of the O2-?V5+and O2-?Eu3+ charge transfer band.The phosphor exhibits a series of red emission of Eu3+ions,and due to the structural change of the host the luminescence intensity ratio 5D0?7F2 to5D0?7F1 is highly dependent on the Eu3+ concentration.Concentration quenching in the phosphor occurs at 30 mol% and the main concentration quenching mechanism are determined to be the exchange interaction.Ba2 La V3O11:Eu3+ displays a tunable emission color from yellow to orange depending on the content of Eu3+,which may have potential applications for lighting and display devices.2)A novel double perovskite tungstate phosphor,Ba6Gd2-x Eux W3O18,was synthesized by a solid-state reaction method.X-ray diffraction(XRD)patterns,scanning electron microscope(SEM)patterns,photoluminescence(PL)excitation,emission spectra and PL decay curves were used to characterize the prepared phosphors.The XRD pattern shows that the phosphor exhibits a pure phase group Fm-3m(225)with a cubic double perovskite structure(space).The SEM image shows a nanowire structure with a diameter ranging from tens to hundreds of nanometers.Excitation and emission spectra indicate that the Ba6Gd2-x Eux W3O18 phosphor exhibits a strong charge transfer band at about 323 nm and strong orange-red emission of Eu3+(5D0?7F1 transition)at 593 nm.The optimum doping concentration of Eu3+ ions in the Ba6Gd2-x Eux W3O18 phosphor is about 20mol%.The main mechanism of concentration quenching is quadruple-quadrupole interaction.