Laser spectroscopy and electron paramagnetic resonance of Cr3+ doped silicate glasses

Gels and glasses in the SiO2–Al2O3–ZnO–Cr2O3 and SiO2–Al2O3–MgO–Cr2O3 systems were synthesized by the sol–gel method. A description of the change of the Cr3+ environment during the xerogel–glass–glass ceramic transformation is presented using optical properties of Cr3+ ions. Absorption and emission spectra, electron paramagnetic resonance measurements, and site-selective laser spectroscopy were performed to characterize the Cr3+ fluorescent centers. Absorption and fluorescence are interpreted by structural considerations showing the variation of Cr3+ environment during heat treatment. By heating glasses, the glass-ceramics containing chromium-doped ZnAl2O4 (gahnite) are formed. The results indicate the presence of chromium ions in a gahnite crystalline phase and emission from the 2E level is observed. Also a Cr3+ fluorescence centered at 770 nm results from 4T2 level of Cr3+ sites at low ligand field in glassy phase.