Microstructure, mechanical, EPR and optical properties of lithium disilicate glasses and glass-ceramics doped with Mn~(2+) ions

摘要

The microstructure, mechanical, EPR and optical properties of transparent MnO_2 doped lithium disilicate (LDS) glass-ceramics prepared by melt quenching and controlled crystallization, have been studied. The microstructure of the glass-ceramics has been characterized using FE-SEM, TEM, FT-IR and XRD techniques. FE-SEM micrographs show elongated, highly interlocked, dense (~80vol.%) nanocrystals of LDS with an average size ~100 nm. XRD and FT-IR studies reveal that the only crystalline phase formed after heat-treatment at 700 °C for 1 h is LDS. A good combination of average microhardness ~5.6GPa, high fracture toughness ~2.8MPam1'2, 3-point flexural strength ~250MPa and moderate elastic modulus 65 GPa has been obtained. The EPR spectra of both LDS glasses and glass-ceramics exhibit resonance signals with effectiveg values at g=4.73, g=4.10, g=3.3, andg=1.98. The resonance signal atg=1.98 is found to be more intense than the other signals and exhibits hyperfine structure at lower concentration of manganese. From the observed spectrum, the spin-Hamiltonian parameters have been evaluated. In glass samples the optical absorption spectrum exhibits a broad band around ~20,320 cm-1 which has been assigned to the transition ~6A_(1g)(S) -> ~4A_(1g)(G) ~4E_g(G)-of Mn~(2+) ions. The cerammed samples upon 394 nm excitation emit a green luminescence (565 nm, ~4T_(1g) -> ~6A_(1g)(G) transition of Mn~(2+) ions), and a weak red emission (710nm). From the ultraviolet absorption edges, the optical bandgap energies (E_(opt)) were evaluated and are discussed.