Raman scattering, absorption and luminescence spectroscopy of CoSiF6·6H2O crystal and CoSiF6·6H2O:Mn4+ red-emitting phosphor

CoSiF6·6H2O and CoSiF6·6H2O:Mn4+ crystals were investigated by means of Raman, optical absorption, and luminescence spectroscopy. Absorption spectra of CoSiF6·6H2O are analyzed by Tanabe-Sugano technique and are proved to be well-describable at crystal field strength Dq = 1000 cm−1, and Racah parameters B = 896 cm−1, C = 4408 cm−1, Dq/B = 1.116. Raman spectroscopy reveals a phase transition associated with the ordering of both the CoO6 and SiF6 octahedra, which occurs through the ordering of the H2O subsystem. Luminescence spectrum of Mn4+ ions in CoSiF6·6H2O lattice consists of six components corresponding to Stokes and anti-Stokes emission from 2E state of Mn4+ ion at vibrational frequencies of MnF6 octahedron ν6 = 230 cm−1, ν4 = 335 cm−1, and ν3 = 645 cm−1. Quantum efficiency of red emission maximizes at excitation wavelength 357 nm and equals to 5%. Decrease of quantum efficiency in comparison to other related materials is explained by absorption of Co2+ ions and non-radiative relaxation in the Co2+ subsystem. •Raman and optical spectra of hydrated cobalt silicon fluoride were studied.•Optical spectra of Co2+ are well interpretable in d7 Tanabe-Sugano model.•Mn4+ ions enter the Si sites in the lattice.•Red Mn4+ luminescence with maximum 5% PLQY is obtained that is explained by non-radiative relaxation in Co system.