Luminescent properties of Eu$^{3+}$-doped yttrium or gadolinium phosphates

After an investigation of the formation conditions of the intermediate phases existing in the systems Y$_{2}$O$_{3}$-P$_{2}$O$_{5}$ and Gd$_{2}$O$_{3}$-P$_{2}$O$_{5}$ (R/P = 4/1, 3/1, 1, 1/2, 1/3 and 1/5 (R = Y or Gd)) the luminescence characteristics of the Eu$^{3+}$ ion substituted for the Y$^{3+}$ or Gd$^{3+}$ ions have been determined. The position of the O$^{2-}\!\to$Eu$^{3+}$ charge transfer band shifts to higher energies with increasing P content, which results in high quantum efficiencies for several P-rich phosphates. With increasing P content the probability of the electric dipole transitions is reduced, in particular for the hypersensitive $^{5}$D$_{0}\to ^{7}$F$_{2}$ transition. This causes a shift of the colour point to the orange and lengthens the luminescence lifetime. The luminescence characteristics are compared with those of the red phosphors for display