Effect of Synthesis Conditions on the Optical Properties of Luminophors NaGdGeO4 and NaYGeO4:Tm3+, Bi3+, or Bi3+/Eu3+

The samples of NaGdGeO4, NaY0.975Tm0.025GeO4, NaY0.975Bi0.025GeO4, and NaY0.875Bi0.025Eu0.1GeO4 have been prepared by different methods. According to X-ray powder diffraction, germanates crystallize in orthorhombic syngony (space group Pnma, Z = 4). We have assessed effect of synthesis conditions on the surface and optical properties of the samples, in particular, the samples were molded by exposure to heat and microwave radiation, the luminescent properties of the compounds have been studied in the near IR region (1100–2100 nm, λex = 808 nm) for NaY0.975Tm0.025GeO4, in the UV region (300–320 nm, λex = 257 nm) for NaGdGeO4, and in the UV–Vis region (300–700 nm, λex = 298 nm) for NaY0.975Bi0.025GeO4 and NaY0.875Bi0.025Eu0.1GeO4. In the latter case, we have studied effect of annealing conditions on persistence duration.