Synthesis and characterization of four new europium group XIV chalcogenides: K(2)EuTSe(5) and KEuTS(4) (T = Si, Ge).

Abstract

Four europium group XIV chalcogenides have been synthesized using the reactive flux method: K(2)EuTSe(5) (I, II) and KEuTS(4) (III, IV) where T = Si, Ge. K(2)EuSiSe(5), I, crystallizes in the monoclinic space group P2(1)/c with cell parameters a = 11.669(3) A, b = 9.844(2) A, c = 8.917(2) A, beta = 91.583(5) degrees, and Z = 4. K(2)EuGeSe(5), II, crystallizes in the monoclinic space group P2(1)/c with cell parameters a = 11.8056(3) A, b = 9.9630(1) A, c = 8.9456(1) A, beta = 91.195(1) degrees, and Z = 4. Both K(2)EuSiSe(5) and K(2)EuGeSe(5) are semiconductors with optical band-gaps of approximately 2.00 and 1.84 eV, respectively. Raman spectroscopy shows vibrations from the (TSe(5))(4-) (T = Si, Ge) unit. KEuSiS(4), III, crystallizes in the monoclinic space group P2(1) with cell parameters a = 6.426(4) A, b = 6.582(5) A, c = 8.566(7) A, beta = 107.83(6) degrees, and Z = 2. KEuGeS(4), IV, crystallizes in the monoclinic space group P2(1) with cell parameters a = 6.510(2) A, b = 6.649(2) A, c = 8.603(3) A, beta = 107.80(2) degrees, and Z = 2. Band-gap analysis shows that both compounds are semiconductors with optical band-gaps of 1.72 and 1.71 eV, respectively. The Raman spectrum of KEuGeS(4) shows the vibrations of the (GeS(4))(4-) unit. Fluorescence spectroscopy confirms the presence of Eu(III) in III and IV instead of Eu(II) as in I and II. These four crystalline products were formed under equivalent stoichiometric reaction conditions. The fact that two different products are observed can be used to understand the relationship between the oxidative and reductive potentials within these flux reactions.