Properties of Na2SiF6:Mn4+ and Na2GeF6:Mn4+ red phosphors synthesized by wet chemical etching

We report a simple method of synthesizing red phosphors, Na2SiF6:Mn4+ and Na2GeF6:Mn4+, by wet chemical etching of Si wafers and Ge shots in aqueous HF solution with the addition of an oxidizing agent NaMnO4. The x-ray diffraction analysis suggests that the red phosphors have the trigonal structure (space group=D-3(2) - P321). The optical properties of these phosphors are investigated using photoluminescence, photoluminescence excitation, optical absorption, and diffuse reflectance spectroscopy. The spectral features show no clear difference between Na2SiF6:Mn4+ and Na2GeF6:Mn4+ phosphors. They are well explained by the Tanabe-Sugano energy-level diagram with the crystal-field and Racah parameters of Dq similar to 1970 cm(-1), B similar to 775 cm(-1), and C similar to 3490 cm(-1) with C/B similar to 4.5. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3056375]