Structural and morphological characterization of Pr and Er-containing SiO2-P2O5 sol-gel thin films

Present work is focused on obtaining and characterization of sol-gel thin films belonging to SiO₂-P₂O₅-Er₂O₃ (I) and SiO₂-P₂O₅-Pr₂O₃ (II) systems. The films have been obtained by spin coating technique for three rotation speeds: 2000, 3500 and 5000 rpm. The deposition of the films was performed at different periods of time, i.e. 24 h, 96 h, 120 h, 144 h and 168 h after instant preparation of the precursor sols. FTIR (Fourier transform infrared spectroscopy) and Raman characterization aimed at investigating the structural changes that occurred in silicophosphate network in dependence on the spin rate of the substrate as well as on the time period elapsed since the sol preparation till the deposition day. FTIR spectra recorded in the 400-4000 cm⁻¹ range revealed Si-O-Si, P-O-P and Si-O-P vibration modes and optical phonons specific for OH units. Raman spectra collected in the 100-4000 cm⁻¹ range put in evidence stretching, bending and mixed vibration modes specific for silicophosphate network as well as rare-earth ion peaks specific to certain electronic transitions. Morphological investigation made by AFM (atomic force microscopy) on Er and Pr-doped silicophosphate sol-gel films evidenced specific features depending on the parameters mentioned above and SEM (scanning electron microscopy) analysis revealed micron sphere structural units, exfoliation of the films and micro cracks.