BLUE LUMINESCENCE IN MIXED YTTRIUM AND GADOLINIUM NIOBATES CAUSED BY BISMUTH. THE ROLE OF THE ns~2 IONS

摘要

From Fig. 1, the CL luminescence for the mixed materials is no better than that of the pure YNbO_4:Bi material. Hence the addition of Gd to the lattice degraded the luminescent properties, even though it promised to change the wavelength. Indeed from Fig. 4, it is apparent that the wavelength of the emission peak can be made more blue by the inclusion of Gd in the lattice, so from that point the study was successful. The fact that a gradual change in properties is seen across the system is significant and shows that the Bi~(3+) (6s~2) ions are behaving the same way throughout the mixed Y -Gd system. Comparing the initial characteristics of oxides, it is clear that this blue phosphor is inferior to ZnS:Ag. However such sulphide phosphors are not practical under high current loading, as the release of sulphide during maintenance degrades the FED electrodes. Oxides show greater promise. The best oxide based blue phosphor to date is Y_2SiO_5:Ce (P47). The Y_(0.995-x)Gd_xBi_(0.005)NbO_4 materials are brighter but the saturated blue colour is not as good. However because of the known refractory properties of NbO_4 maintenance under high loading is expected to be good. Measurements so far have been D. C. and saturation has not been fully assessed. It is clear that the niobates and related compounds have potential for further improvement.