Cyclogermanate Sr_3La_2(Ge_3O_9)_2, isostructural to silicate Sr_3Er_2(Si_3O_9)_2, activated by neodymium and holmium is obtained for the first time by the precursor method. Ion Nd^3+ in the structure of Sr_3La_2(Ge_3O_9)_2 is a sensitizer of the infrared luminescence of Ho^3+. Excitation by radiation with a wavelength of 808 nm leads to a series of emission lines in the luminescence spectra of Sr_3La_2- x Nd_ x (Ge_3O_9)_2 : Ho^3+ in the short-wave and middle-IR ranges (1.0–3.4 μm). The highest intensity of lines at 2.1 and 2.7 μm, associated with the ^5 I _7 → ^5 I _8 and ^5 I _6 → ^5 I _7 transitions in the Ho^3+ ion, is found for compositions containing traces of holmium. Based on the analysis of the concentration dependences of the luminescence intensity, an optimal composition of the phosphor is determined, which ensures the maximum efficiency of conversion of laser radiation energy. The data obtained are interpreted in the assumption of cross-relaxation energy transfer from Nd^3+ to Ho^3+.

Triorthogermanates BaYb2-xErxGe3O10 (x = 0.1–0.3) and BaY2-10yYb9yEryGe3O10 (y = 0.015–0.15) have been synthesized by the solid-state method. According to X-ray powder diffraction data, the compounds crystallize in the monoclinic system, S.G. P21/m, Z = 2. The concentration and power pump dependences studies have been carried out for the lines in the 510–720 nm spectral range under 980 nm excitation. The mechanisms of energy transfer between optical centers have been also proposed and the optimal composition of the phosphor has been determined. The influence of temperature on the intensity ratio of the luminescence bands with maxima at 521 nm and 552 nm (2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions in Er3+) has been investigated, and conclusions about the possibility of using the germanates as materials for optical temperature sensors have been drawn.

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The analysis of the unified series of single-phase Zn_2 – 2 x Mn_2 x SiO_4 samples ( x ≤ 0.2) has provided the possibility to determine the optimal dopant concentration x = 0.13 for the maximum luminescence intensity. It has been established that the dominating mechanism of concentration luminescence quenching and excitation energy dissipation is the oxidation of some Mn^2+ activating ions and the growth of defectness in the luminophore due to this process Phosphors.

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