Ti-doped MgAl 2 O 4 spinel single crystals grown by the micro-pulling-down method for laser application: Growth and stro
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Georges Boulon and Gérard Panczer Physical Chemistry of Luminescent Materials, UMR CNRS 5620, Claude Bernard / Lyon 1 University, Villeurbanne 69622, France
Kiyoshi Kato and Eiichi Hanamura Chitose Institute of Science and Technology, 758-65, Bibi Chitose-city, Hokkaido 066-8655, Japan (Received 28 November 2005; accepted 19 May 2006)
The photoluminescence spectra of the rod-shaped pure and Ti-doped MgAl2O4 single crystals, grown by the micro-pulling-down (-PD) method, have been systematically investigated under high-intensity pulsed Nd3+: YAG laser excitation in the ultraviolet (UV) region (266 nm). The chemical properties of the grown crystals under reducing argon atmosphere will be reported and the annealing effect under oxidizing atmosphere will be discussed. The room temperature luminescence properties of Ti-doped MgAl2O4 single crystals were performed before and after annealing as a function of the titanium concentration. Three broad bands absorption in the UV/VIS (visible) spectral regions and a broadband visible blue emission were observed from Ti-doped MgAl2O4. An estimation of the decay time value of theses emissions was determined from the time-resolved spectra and the energies of the vibrational modes of the MgAl2O4 crystal are obtained from the infrared spectra.
I. INTRODUCTION
In recent years, new solid-state laser materials working in the visible region are needed for ultrafast optical devices in science as tunable solid-state lasers, and technology as matrix for fiber-optic temperature sensors or a substrate for microelectronics. The magnesium aluminum spinel MgAl2O4 is known to be an attractive oxide material with a combination of desirable properties of high melting point, high strength, high hardness, resistance to corrosion, and low electrical losses and it can be easily activated by transition-metal ions like cobalt (Co2+) or chromium (Cr3+) for optical devices: with the saturable absorption in the eye-safe spectral range, Co2+doped MgAl2O4 crystals can be used as a media for passive Q-switch of lasers, which operates in the spectral range of 1.3–1.6 m, for example 1.32 m Nd:YAG and 1.54 m erbium glass lasers,1 and the Cr3+-doped stoichiometric or non-stoichiometric MgAl2O4 spinel have been well studied for tunable solid-state laser applications.2 Recently, Aizawa et al.3 have shown that Cr3+doped MgAl2O4 is potentially powerful material for a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0280 J. Mater. Res., Vol. 21, No. 9, Sep 2006
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fiber-optic thermometer with high temperature sensitivity due to large temperature coefficient. On the other hand, titanium-doped sapphire has been reported to be the first and one of the successfully commercial solidstate laser material in which Ti3+ is the active laser ion4; the short lifetime of the upper laser level in the s range represents the major problem for flash lamp pumping of Ti3+-doped Al2O3, because short pulses require a high peak
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