ORIGIN OF THE INFRARED ABSORPTION IN LaMgAl11O19 : Ti3+ A POTENTIAL LASER MATERIAL

The LaMgAl11O19 matrix (magnetoplumbite structure) activated with Ti3+ could present broadly tunable laser action between 650 and 1000 nm. The optical absorption measurements show, in addition to the 2T2࢐2E transition of Ti3+, two unexpected infrared bands. The first one, peaking at 730 nm, is attributed to an intervalence charge transfer transition of Ti3+ - Ti4+ pairs located in (4f) sites. The second one, at 960 nm, is attributed to a Ti2+ - Ti3+ charge transfer transition. These bands which occur in the range of the Ti3+ fluorescence wavelengths have to be suppressed for the lasing application of this material

Optical properties of Tm3+ in the gehlenite matrix and sensitization of Ho3+ luminescence in potential Tm/Ho lasers

The Tm:Ho solid state lasers pumpable by laser diodes and emitting around 2.1 µm present interesting applications. In the Ca2Al2SiO7 (CAS) gehlenite host, we have studied the Tm3+ emission, strongly dependent of the doping concentration, the Tm3+-Tm3+ energy transfer leading to the 3F4 → 3H6 broad emission [λmax = 1780 nm, using the [3H4,3H6] →[3F4,3F4] cross-relaxation scheme]. Furthermore, the Tm3+-Ho3+ interactions have also been demonstrated in this study

CRYSTAL GROWTH AND OPTICAL PROPERTIES OF LaMgAl11O19 : Cr, Nd

Single crystals of chromium and chromium-neodynium codoped lanthanum-magnesium hexa-luminates LaMgAl11O19 have been pulled through the Czochralski method up to diameters 25 mm and lenght 75 mm

OPTICAL PROPERTIES OF Cr3+ ION IN LaMgAl11O19 and La1-x Ndx MgAl11O19

Lanthanum-magnesium hexaaluminate LaMgAl11O19 with magnetoplumbite-like structure is a remarkable good laser host for Nd3+ ions (LNA). In this study Cr3+ ions are introduced as an activator (LaMgAl11-xCrxO19) or as a sensitizer (La1-xNdxMgAl11O19) in this matrix. ESR and optical spectra of LaMgAl11-xCrxO19 crystals reveal 3 kinds of sites for Cr3+ : (4f), (2a) and (12k). The presence of 4T2 - 4A2 broad band fluorescence makes this material a possible candidate for a red or IR emitting vibronic laser. Optical properties of La1-xNdxMgAl11O19 reveal that both radiative and non-radiative Cr3+ - Nd3+ energy transfers occur in this material. This allows to increase the laser emission ratio compared with single doped LNA

Crystal growth and optical properties of Er:CAS (Ca2Al2SiO7) and Er:SLG (SrLaGa3O7)

The optical properties of Er3+ doped Ca2Al2SiO7 (CAS) and SrLaGa3O7 (SLG) are described in this paper. Er3+ solubility is determined for the two laser hosts. Cross-relaxation processes and multiphonon desexcitation are observed and the relative rates are calculated with the frame of the Judd-Ofelt analysis. Er:SLG presents some longer lifetimes and smaller multiphonon non radiative contribution than the Er:CAS. Both laser hosts present a broad and intensive emission around 1.5 µm. In this paper are also discussed the mechanisms that can reduce the laser oscillation efficiency

FLUORESCENCE OF Pr3+ AND Dy3+ IN LaMgAl11O19 SINGLE CRYSTALS

LaMgAl11O19 doped with Pr3+ could lead to a material lasing in the visible range. For lamp pumping it is necessary to sensitize the fluorescence (for example by Dy3+). Optical properties have been determined by absorption, diffuse reflectance, fluorescence spectroscopies as well as fluorescence decays on 2 kinds of materials : single doped crystals La1-xLnxMgAl11O19 (Ln = Pr, Dy) and codoped ones La1-x-yPrxDyyMgAl11O19. In single doped material a strong fluorescence quenching occurs. In codoped crystals, while fluorescent levels of Dy3+ are in resonance with Pr3+ absorption levels, there is no sensitization of the Pr3+ fluorescence

PHYSICAL PROPERTIES AND TUNABLE LASER ACTION OF VERNEUIL GROWN SINGLE CRYSTALS OF Al2O3 : Ti3+ (Preliminary data)

No abstract availabl

A study of chromite carbochlorination kinetics

International audienceThe carbochlorination of a chromite concentrate was studied between 500 °C and 1000 °C using boat experiments. The reaction products were analyzed by scanning electron microscopy (SEM), x-ray diffraction (XRD), and chemical analysis. The carbochlorination of a chromite concentrate at about 600 °C led to the partial selective elimination of iron, thus increasing the Cr/Fe ratio in the treated concentrate. Total carbochlorination of the chromite concentrates and volatilization of the reaction products was achieved at temperatures higher than 800 °C. The kinetics of the chromite carbochlorination was studied between 750 °C and 1050 °C using thermogravimetric analysis (TGA). The results were discussed in terms of the effects of gas flow rate, temperature, partial pressure of Cl2+CO, and Cl2/CO ratio on the carbochlorination process. It was observed that the temperature effect changed significantly with the progress of the reaction. The initial stage of the carbochlorination was characterized by an apparent activation energy of about 135 and 74 kJ/mol below and above 925 °C, respectively, while a value of about of 195 kJ/mol was found for the remainder of the carbochlorination process