Chromium-doped

The term laser is an acronym constmcted from light amplification by stimulated emission of radiation. The first operating laser was produced in 1960 (1). This laser, which used a crystal of mby [12174A9-17, chromium-doped alumina, Al202 Cr, and emitted a pulsed beam of collimated red light, immediately aroused scientific interest. 

Borgarello, E., Kiwi, J., Graetzel, M., Pelizzetti, E., Visea, M. 1982. Visible-light induced water eleavage in colloidal solutions of chromium-doped titanium-dioxide partieles. J Am Chem Soe 104 2996-3002. 

Cr-doped Ti02 has been widely studied for photoanode application since addition of Cr shifts the optical absorption spectrum towards the visible range, with the caveat that excess chromium doping leads to higher recombination rates. Various synthesis methods have been employed to date. For example Radecka an coworkers used r.f. sputtering to prepare up to 16 at% Cr-doped Ti02 [70]. XRD reveals that at low Cr concentration the... 

Domenech A, Torres FJ, Ruiz de Sola E, Alarcon J (2006) Electrochemical detection of high oxidation states of chromium(lV and V) in chromium-doped cassiterite and tin-sphene ceramic pigmenting systems. Eur J Inorg Chem 638-648. 

A new class of lasers, so called vibrionic solid state lasers, can emit—in contrast to mher solid slate lasers—a comparatively broad range of wavelengths. The lower level in these lasers is a band of energy levels that is caused by interaction between the electron motion and lattice vibrations. With ihe help of Ihe usual tools (filters, ctalons etc.) a narrow and tunable frequency bandwidth is selected for the laser output. The most popular materials arc Ti-sapphire. i.e.. titanium doped Al-Oi with output range from hOO to 118(1 nm and Alexandria. i.e.. chromium doped BeAFOi lasing between about 700 and 825 nm. 

The chromium doped catalysts had also a marked influence on the products obtained, affording a higher selectivity in pentylamine it was increased... 

For certain special purposes, e.g., the excitation of resonance Raman spectra, tunable dye lasers and solid state lasers are used, e.g., the chromium doped Alexandrite laser and the titanium doped sapphire laser (Demtroder, 1991). 

Emerald (Cr3+ Be3Al2(Si03)6, chromium-doped beryllium aluminium silicate or beryl) is a well known gem, and its beautiful green color has been attracted people for a long time. Nowadays, emerald crystal is also known as a tunable solid-state laser material, and its optical properties have been smdied (1-10). 

In solid-state laser materials, such as ruby (chromium doped alumina, AljOjiCr " ) (1) and emerald (chromium doped beryl, Be,Al,(Si03)5 Cr ) (2), transitions between multiplets of impurity states are utilized. These states mainly consist of 3d orbitals of the impurity chromium ions. For the analysis of these multiplet structures, the semi-empirical ligand-field theory (LFT) has been frequently used (3). However, this theory can be applied only to the high symmetry systems such as O, (or T ). Therefore, the effect of low symmetry is always ignored in the analysis based on the LFT, although most of the practical solid-state laser materials actually possess more or less distorted local structures. For example, in ruby and emerald, the impurity chromium ions are substituted for the aluminum ions in the host crystals and the site symmetry of the aluminum ions are C, in alumina and D, in beryl. Therefore, it is important to clarify the effect of low symmetry on the multiplet structure, in order to understand the electronic structure of ruby and emerald. 

The observation of space charge limited currents (SCLC) in nanoscaled pure and chromium-doped titania was reported [310] and both the free-charge carrier density and the trapped-charge carrier density were given. 

P.E. Childs and J.B. Wagner Jr., Chemical diffusion in wustite and chromium-doped manganous oxide, in G.R. Beltane and W.L. Worrell (Eds.), Heterogeneous Kinetics at Elevated Temperatures. Plenum Press, New York, 1970, pp. 269-342. 

Chromium Doping. Additions of chromium compounds can be used to produce very fine metal powder grades (<0.5 pm). Chromium oxide is formed during reduction and acts as a grain refiner. Such powders are subsequently carburized to ultrafine WC. Special precautions have to be taken because of the high pyrophoricity of the metal powder. 

Interestingly, electrochemical data can provide information on the oxidation state of doping centers, as described for high oxidation states of chromium in chromium-doped cassiterite (SnOj) and tin-sphene (or malayaite, CaSnSiOj Domenech et al., 2006c). 

Ardizzone, S., Bianchi, C.L., and Galassi, C., Chromium doped Y-AI2O3 powders. Features of the electrical double layer and state of the surface species, J. Organometall. Chem., 490, 48, 2000. 

One other notable method has been used in the preparation of mixed transition metal molybdates, amongst many other oxide systems. This novel method(TT) involves preparation of the mixed metal oxides via an amorphous precursor such as a citrate salt of the appropriate metals, and then thermal decomposition of the complex to yield the resulting mixed oxides. The experimental procedures are described in four French patents(78-81), giving details of many different preparations including a proposed M0O3 rich, chromium doped iron molybdate, prepared as a possible selective oxidation catalyst. 

Free flowing powder was used. It was prepared by the alumn process at CKB Bitterfeld for the undoped material or at ESCETE Enschede for the chromium doped alumina powder, especially. 

The crystals were embedded in epoxy, cut longitudinal and polished using diamond spray down to a grain size of 3 pm. Fig. 2b shows a SEM image of a crystal with a gradient in the chromium doping. In this case a crystal with a sharp transition was investigated. 

Ruby chips —40 jim square, 0.5 wt % chromium doped Sewing needles... 

These estimates give only an upper limit of oxygen permeation rate because surface exchange reactions may result in some suppression of the overall transport. For the conditions typical for syngas generation (pO2=0.21 atm, pOj = 10 atm, 950°C), the results for the membranes with L = 0.1cm and different chromium contents are shown in Fig. 3. In the calculations at high pressures the ion conductivity values were assumed to be nearly equal to those at low pressures. Fig. 2. It is seen that the permeation rate in chromium doped samples is smaller than in the parent ferrite. Nonetheless, it may achieve a value of about 4 ml cm min in the sample with y = 1, which corresponds to the syngas production rate of about 20-25 ml-cm -min in the methane partial oxidation process. In combination... 

Bamabe A., Maignan A., Hemieu M., Damay F., Martin C., Raveau B. Extension of colossal magnetoresistance properties to small A site cations by chromium doping in Lao.sCao.sMnOs manganites, Appl. Phys. Lett, 1997, V.71, No 26, p.3907 - 3909. 

---