| White light-emitting diodes are considered as the new generation of solid-state lighting sources due to their unique properties including but not limited to environment-friendliness, energy savings, small volume, and long persistence. Currently, white LED excited by NUV-LED shows better color-rendering index, thus, it becomes the hotspot of the present research at home and abroad. But it has new problems of reabsorption of emission colors and ratio regulation for each phosphor. Using single matrix or decreasing the species of phosphors can solve the problem.MgAl(PO4)O, a special monoclinic crystal, not only has the excellent properties such as low synthesis temperature, high physical-chemical stability, but also has special structure as the phosphor host. The aim of this thesis is to synthetize Eu doped MgAl(PO4)O and investigate its luminescence properties.In Eu doped system, MgAl(PO4)O:Eu3+and MgAl(PO4)O:Eu2+are synthetized by high temperature solid-state method. Their synthetized conditions, the effect of concentration of Eu on luminescence properties and color coordinates are investigated. The red emission at594nm of the MgAl(PO4)O:Eu3+is dominant under394nm excitation. Peak form and position will not change when the concentration of Eu3+changes. MgAl(PO4)O:Eu2+shows blue luminescence with the broad band around430nm and low green emission around520nm under365nm excitation. Blue shift can be abserved when increasing the concentration of Eu2+. The color coordinates of Mg1-xAl(PO4)O:xEu2+change from blue-green to blue region.In order to obtain white light emission, we futher study the factors and methods of two ways to achieve white light emission. The results showed that:because of the wide color gamut, white light emission and color adjustment are got only by mixing MgAl(PO4)O:Eu2+and MgAl(PO4)O:Eu3+. Among them, the color coordinates of the smple which the mixing ratio is one to one is (0.327,0.336), very close to color coordinates of standard white light (0.333,0.333). The red emission of Mn2+sensitization by Eu2+is found in Eu/Mn co-doped system. Both white light and different color can be obtained by adjusting the concentration of Mn2+. For the expansion of the structural characteristics and luminescence properties of the phosphor, the phosphor in which Mg is replaced by other alkaline earth metal ions are synthetized and their luminescence properties are investigated. But the samples in which Mg is replaced totally by Ca, Sr and Ba do not have the similar structure with MgAl(P04)O but are mixture of different phase. But on the other hand, both Eu2+and EuJ+are found in the phosphor in which alkaline earth metal ions doped by low concentrations (5%mol). We thought that the reason of the appearance of Eu2+is the cation site replaced by other alkaline earth metal ions having the ability of self-reduction. The degree of the self-reduction increase with the radius of doping cation increasing, The above results show that part of the cation replacement can achieve regulating not only valence state of Eu but also color. It provides an effective way to synthetize new type of phosphor and adjust its color.In this thesis, valence state of Eu and color can be adjusted by atmosphere and alkaline earth metal ions doping in Eu doped MgAl(P04)O. Moreover, white emission is obtatin by mixing blue and red phosphors or Eu2+/Mn2+co-doped phosphors which are expected to be applied as the new phosphor for white LED. |
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