Local chemical environment of Pr3+ substitutional defects in bulk and nanocrystalline Gd3Ga5O12:: A joint EXAFS and luminescence study

A joint approach using EXAFS (extended X-ray absorption fine structure) and luminescence results has been used to obtain information on the local structure and the electron-phonon coupling of the Pr3+ ion in bulk and nanocrystalline gadolinium gallium garnet samples. The nanocrystalline sample is prepared with a combustion synthesis, whereas the bulk sample is prepared by a sintering procedure using the nanocrystalline powders. EXAFS measurements show that the Pr-O distances are similar for the bulk and the nanocrystalline samples but a notable amount of static disorder in the first coordination sphere of the dopant is found to be present in the nanocrystalline sample. From the behavior of the emission line width and shift of a Pr3+ emission band as a function of the temperature, the electron-phonon coupling strength of the Pr3+ ion has been evaluated. The electron-phonon coupling strength results to be notably stronger for the nanocrystalline sample than for the bulk one. This behavior is attributed to the fact that the local surrounding of the Pr3+ ion is softer for the nanocrystalline sample than for the bulk one.