Influence of synthesis conditions on the optical properties of Naregeo<sub>4</sub> phosphors with olivine structure

The NaGdGeO4, NaY0.975Tm0.025GeO4, NaY0.975Bi0.025GeO4, NaY0.875Bi0.025Eu0.1GeO4 samples were synthesized by different methods. According to powder X-ray diffraction data, the germanates crystallize in orthorhombic system pr.gr. Pnma, Z = 4. The influence of synthesis conditions, particularly different annealing modes, on morphological and optical properties of the samples were evaluated. The luminescence properties of NaY0.975Tm0.025GeO4, NaGdGeO4 and NaY0.975Bi0.025GeO4, NaY0.875Bi0.025Eu0.1GeO4 compounds were studied in the near infrared range (1100 – 2100 nm, λex = 808 nm), in the UV region (300–320 nm, λex = 257 nm) and in the UV and visible wavelength range (300 – 700 nm, λex = 298 nm), respectively. The influence of annealing parameters on the persistent luminescence duration of the last compositions was investigated additionally.