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Titanium doped sapphire (Ti:Al2O3) shows a 420 nm blue emission band whose corresponding excitation band lies at 244 nm. With the aim of ascertaining the origin of this blue emission, using synchrotron radiation we measured the vacuum ultraviolet to ultraviolet absorption spectrum of titanium doped sapphire. It is suggested that the blue emission is due to a center other than a trivalent Ti3+ ion or a tetravalent Ti4+ ion, most probably an F+-type color center formed in the crystal.

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The luminescent properties of Gd 2 SiO 5 powder crystals doped with Eu 3+ were investigated using synchrotron radiation and a VUV laser (157.6 nm) as excitation sources. The excitation spectra in the range of 160-330 nm monitoring the red emission from Eu 3+ ions reveal bands corresponding to intraconfigurational 4f-4f transitions of Gd 3+ and charge transfer states (CTS) of Eu 3+ -O 2− , as well as interband transitions of the Gd 2 SiO 5 host, indicating an efficient energy transfer process from the host or directly from Gd 3+ to Eu 3+ ions. The inspection of 5 D 0 → 7 F 0 emission lines from Eu 3+ ions suggests that there are three inequivalent sites for Eu 3+ in this host. The excitation band around 215 nm and the unique emission features associated with this excitation band were attributed to one of the inequivalent Eu 3+ sites, which exhibits an unusually weak coupling with host lattice. The energy levels of Eu 3+ in the Gd 2 SiO 5 host were tentatively assigned according to the laser excited emission spectra.