Polymorphism in Gd2Ge2O7 ceramics: Structural, vibrational, and optical features

In this work, Gd2Ge2O7 polymorphs were obtained by solid-state reactions at 1100?1300 ?C. Structural and vibrational features were investigated by X-ray diffraction and Raman spectroscopy. For the triclinic (space group P1) polymorph, all the predicted phonons were discerned in perfect agreement with the group theory calculations, while for the tetragonal polymorph (space group P41212), 53 bands of the 81 predicted modes could be identified and characterized. The Gd3+ 4f-4f electronic transitions were investigated by diffuse reflectance spectroscopy in the range 200?340 nm. By applying the Kubelka-Munk function, it was possible to determine the bandgap values for all ceramics studied. The tetragonal polymorph exhibited higher bandgap values (5.88 eV) than the triclinic one (5.59 eV), which are both more energetic than other pyrochlore polymorphs reported in the literature. The results indicate that the presence of polymorphism in Gd2Ge2O7 ceramics can be used to produce tailor-made materials since their crystal structures have a strong influence on their optical properties. Consequently, these properties could be used to tuning the optical properties of Gd-containing materials to sensitize and transfer energy to other luminescent lanthanide ions, aiming for innovative applications.

Automated summary

In this study, Gd2Ge2O7 polymorphs were obtained by solid-state reactions and their structural and vibrational features were investigated. The electronic transitions of Gd3+ 4f-4f were examined by diffuse reflectance spectroscopy and bandgap values were determined using the Kubelka-Munk function. The results showed that polymorphism in Gd2Ge2O7 ceramics can be utilized to tailor materials with specific optical properties.