In this research, phosphors for fluorescent-type displays such as field emission displays (FED) and vacuum fluorescent displays (VFD) were studied. Phosphors mainly studied were promising blue emitting phosphors, that is, $YNbO_4:Bi$ and $Y_2SiO_5:Ce$. It was focused on the luminescence increase of the promising phosphors by using a co-doping technique applied to the host materials. In addition to the luminescence increase, it was tried to explain the relationship between the crystal structure of phosphors and its luminescence.
The co-doping technique used to attempt to increase the luminescence intensity of $YNbO_4:Bi$ turned out to be not so effective. However, surface modification using an acid was found to effectively increase the luminescence efficiency of $YNbO_4:Bi$. It have been investigated the existing phases in the yttrium silicate system, not only by X-ray powder diffraction but also by PL and CL measurements. The main band shift of high-temperature-phase $Y_2SiO_5:Ce$ is observed when the number of large $Ce^{3+}$ ions is more than that of nonluminescencing small $Ce^{4+}$ ions under a reduction atmosphere.
Also, aging behaviors of the promising oxide phosphors were studied. From aging behaviors, it was found that the internal efficiency of phosphor is related to the aging behaviors of phosphors. Also, it was found that some $ABO_3:Pr^{3+}$ phosphors emitted various colors from the energy level of Pr3+ ion. Among them, $SrSnO_3:Pr$ and $CaSnO_3:Pr$ were tentatively suggested as potential white phosphors.
Finally, as a conclusion of this research, the co-doping map was suggested as a meaning of help to increase a luminescence intensity of oxide phosphors.
