Synthesis And Luminescent Properties Of Nuv-excited Phosphors Based On Borophosphates For White LEDs

As the fourth generation light source,white-LEDs will be the main lighting source in future because of resource saving,environmentally friendly and so on.As compare with the commercial way for white-LEDs,which realized by employing blue LED chips coated with yellow phosphors,the near ultraviolet LED chips has more higher energy and excited efficiency.Furthermore,this way offers better advantage on color rendering index and stable color temperature.Therefore,as an important part of white-LEDs,looking for a phosphor which could be efficiently excited by near ultraviolet is urgent.Borophosphates are a novel material that based on phosphate and borate,the physical and chemical stability of borophosphates was stable.Furthermore,this kind of material has low synthesis temperature and high color rendering,it is mean that borophosphates will be a new alternative phosphor for near ultraviolet excited.In this thesis,a series of phosphor of borophosphate was synthesized by high temperature solid state reaction.The crystal structure,energy transfer,luminescent property of the phosphors were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM)and photoluminescence spectroscopy.The main work and achievements are summarized as following:1.A series of Cd3BPO7::xDy3+,yTm3+ phosphors were synthesized by solid state reaction.The Cd3BPO7:xDy3+ have the typical 4F9/2→6H13/2 and 4F9/2→6H15/2 emission of Dy3+ under 348 nm excited,and the yellow emission is dominate.This means that Dy3+ is priority to occupy the asymmetry Cd sites in the host.The optimal doped concentration x of Dy3+ is 0.02(mole ratio).The Cd3BPO7:xDy3+,yTm3+ phosphor has white light emission and shows color-tunable with different concentration of Tm3+under 363 nm excited.The energy transfer from Dy3+ to Tm3+ was confirmed through luminescent spectra and luminescent lifetime.The optimal doped concentration of x and y are both 0.02(mole ratio)and the chromaticity coordinates of the phosphor were calculated to be(0.331,0.348).2.A series of Cd3BPO7:xEu3+ phosphor were synthesized by solid state reaction.The optimal doped concentration of Eu3+ is 0.03(mole ratio).The concentration quanching critical distance(Rc)between neighboring Eu3+ is 1.47 nm,the mechanism for concentration quenching of Eu3+ is electric dipole-dipole(d-d)interaction,and the Eu3+ replaced only one Cd site in this host.The sample has a typical red emission of Eu3+ under 394 nm excited.The chromaticity coordinates of Cd3BPO7:xEu3+ were calculated and located in the red region of CIE-1931 chromaticity diagram.3.A series of Ba3BP3O12:xDy3+,yTm3+phosphor were synthesized by solid state reaction.The phosphor exhibites several strong sharp absorption peaks between 280～470 nm.Under 348 nm excited,the Ba3BP3O12:xDy3+ phosphor has main yellow emission,and the Ba3BP3O12:0.01Dy3+,yTm3+ phosphor could offer color-tunable white light with red component,the optimal white light was obtained when the concentration y of Tm3+ is 0.02(mole ratio).The chromaticity coordinate of Ba3BP3O12:0.01Dy3+,0.02Tm3+ is(0.333,0.340),which is very close to the standard of National Television Standards Committee(NTSC)(0.333,0.333).