Preparation And Properties Of Oxide Luminescent Materials For NUV-LED

White light-emitting-diodes(WLEDs),a new generation of lighting source,have been widely used due to their high efficiency,environmental friendliness and energysaving properties.Yet,people’s demand for "healthy lighting" increases as science and technology advance and the quality of life improves,leading to higher performance requirements for LED light sources.Especially in the aspect of indoor lighting,in addition to the basic requirement of "high brightness",the light source should also take the "high quality" requirements of high color rendering index,appropriate color temperature and other indicators suitable for human eye health into account.The combination of "near ultraviolet LED chip+multi-color phosphor"(NUV-LED,Near ultraviolet light-emitting diodes)has unique advantages in improving color rendering index and color temperature adjustment,and has gradually become the preferred solution for WLEDs.However,the existing luminescent materials can be applicated for NUV-LED are still limited by some serious shortages,such as poor thermal stability,harsh synthesis process,inappropriate excitation,and the reabsorption of blue or green light.In view of these key problems,two kinds of Eu2+-doped oxide luminescent materials have been studied in this thesis.Through the ion substitution engineering,on the one hand,we improved the thermal stability of green commercial(Sr,Ba)2SiO4:Eu2+ phosphor;On the other hand,a NUV-excited ultra-broad band yellow emission phosphor has been developed,and the effect of ion substitution on their luminescent properties was studied in depth as well.Specific work and main results of this thesis as follows:1.By the substitution of K+ and Na+,a series of Sr0.98-xAxBaSiO4-xFx:0.02Eu2+(A=K,Na;0 ≤x ≤0.4)have been successfully prepared by high-temperature solid-state method under 1400℃ in the reduction atmosphere.The substitution of K+and Na+for Sr2+ in the SrBaSiO4:Eu2+ lattice can improve the sample’s crystallinity and inhibit the energy transfer between emission centers of Eu2+,resulting in a significant increase in the luminescence intensity of the phosphor.Meanwhile,the structure rigidity can be enhanced by the substitution of K+and Na+,which reduces the probability of the autoionization process of 5d electrons at high temperatures.Moreover,due to the introduction of deeper trap levels,by the joint effect of trap compensation mechanism,the thermal stability of SrBaSiO4:Eu2+phosphor can be greatly improved.At 150℃,its emission intensity can reach to 81.48%of that at room temperature.2.Taking fluorophosphate(K,Rb)2CaPO4F as the research object,at a relatively low temperature(750 ℃),a series of(K,Rb)2Ca0.98-xMgxPO4F:0.02Eu2+ luminescent materials were prepared by using the same main group cation substitution.Good singlephase sample can be formed in varying substitution concentration of Mg2+,which can be proved by the X-ray diffraction patterns.After the substitution of Mg2+for Ca2+,by repressing the energy transfer between the emission centers and strengthening the structure rigidity,the emission intensity and thermal stability of(K,Rb)2CaPO4F:Eu2+solid solution was significantly increased,while the emission wavelength of the solid solution can move continuously in the range of 665-487 nm according to the K/Rb ratio.Substituted by Mg2+,the obtained sample of KRbCa0.78Mg0.2PO4F:0.02Eu2+shows an ultra-broad band yellow light emission with an internal and external quantum efficiency of 58.90%and 32.47%respectively,whose emission band covers most of the visible light spectral area except blue light,with the peak at about 580 nm and a 181 nm emission full-width half-maximum.Its excitation band covers the region from NUV to blue light,peaking around 380 nm,which effectively matches the NUV chip.The fabricated NUV-LED device by using this ultra-broad band yellow emission phosphor as the yellow component can emit bright white light with high color rendering index(Ra=92.3),appropriate correlated color temperature(5644 K)and CIE chromaticity coordinates(0.3292,0.3450),and shows excellent color stability under different driving currents,indicating that this ultra-broad band yellow emission phosphor has great application potential in the field of NUV-LED.