μ-Raman and infrared reflectance spectroscopy characterization of (Lu1−xGdx)2SiO5 solid solution single crystals doped with Dy3+ or Sm3+

• Investigation proves increase of disorder in crystals with increase in Gd content.
• The FWHM of modes essentially increases with the rise in the Gd content.
• The increased disorder influences the optical properties of crystals investigated.
• The change in the splitting of the most intense ν1 stretching mode is observed.
• The splitting decreases from 23 cm−1 for LSO:5Dy to 14 cm−1 for 40LGSO:5Sm.

Single crystals of Lu2SiO5:5 at% Dy3+ - LSO:5Dy,(Lu0.6Gd0.4)2SiO5:4 at% Dy3+ - 60LGSO:4Dy and (Lu0.4Gd0.6)2SiO5:5 at% Sm3+ - 40LGSO:5Sm were obtained by the Czochralski method. It was found that the crystallographic structure of investigated crystals is isostructural with Lu2SiO5 which crystallizes in monoclinic system within a space group C2/c. Detailed spectroscopic analysis in a wide spectral region was carried out for these three solid solution crystals using two complementary techniques polarized Raman and infrared reflectance spectroscopy. Additional interesting information for the low-wavenumber range phonons were obtained using an NExT filter. The red shift of almost all modes with increasing gadolinium content was observed. It results from an increase in the lattice constants. The change in the splitting of the most intense symmetric stretching mode ν1 assigned to vibrations of SiO4 tetrahedra was observed with increasing gadolinium content. The spectral distance between the two components of this mode decreased from 23 cm−1 for LSO:5Dy through 20 cm−1 for 60LGSO:4Dy to 14 cm−1 for 40LGSO:5Sm. Analysis of vibrational spectra provides the information about structural changes and increase in crystal structure disorder with increasing gadolinium content. Increasing disorder observed in vibrational spectra indicates the possibility of substantial broadening of spectral lines of optically active ions in luminescence spectra.

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