Structural and luminescence properties of CaxBa1−xGa2S4:Eu2+ chalcogenide semiconductor solid solutions

The structural and luminescence properties of chalcogenide semiconductor CaxBa1−xGa2S4 solid solutions (x=0.1-0.9) doped with 7 at% of Eu2+ ions were studied at room temperature. It was found, that the crystal structure of CaxBa1−xGa2S4 solid solutions varies with the amount of Ca2+ cations and phase transition from cubic to orthorhombic takes place with increase of x value. CaxBa1−xGa2S4:Eu2+ solid solutions exhibit intense photoluminescence in cyan to yellow spectral region depending on x due to 5d→4f electron-dipole transitions in Eu2+ ions. The peak position of the emission band shifts from 506 nm for x=0.1 to 555 nm for x=0.9 and the full width at half maximum of the emission band varies from 62 nm to 72 nm depending on the symmetry of the crystal lattice. The PL excitation spectrum of CaxBa1−xGa2S4:Eu2+ covers the range at half maximum from 310 nm to 480 nm for x=0.1 and to 520 nm for x=0.9. It was shown that long-wavelength shift is caused by influence of the growing crystal field strength on Eu2+ ions.