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

https://doi.org/10.1016/j.optmat.2023.114343

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.