Novel IR Phosphor Based on Sr3La2(Ge3O9)2 : Nd3+,Ho3+ Germanate

Abstract

Cyclogermanate Sr₃La₂(Ge₃O₉)₂, isostructural to silicate Sr₃Er₂(Si₃O₉)₂, activated by neodymium and holmium is obtained for the first time by the precursor method. Ion Nd³⁺ in the structure of Sr₃La₂(Ge₃O₉)₂ is a sensitizer of the infrared luminescence of Ho³⁺. Excitation by radiation with a wavelength of 808 nm leads to a series of emission lines in the luminescence spectra of Sr₃La_2-xNd_x(Ge₃O₉)₂ : Ho³⁺ 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 ⁵I₇ → ⁵I₈ and ⁵I₆ → ⁵I₇ transitions in the Ho³⁺ 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 Nd³⁺ to Ho³⁺.