Titanium excitation spectra

Fig. 29. Photoluminescence spectrum and its excitation spectrum at 77 K of titanium oxide anchored onto porous Vycor glass. (Excitation wavelength and its slit width were 280 nm and 10 nm, respectively. Emission slit width was 10 nm.) The anchored catalyst was degassed at 423 K and anatase Ti02 powder was degassed at 573 K.

Some examples of luminescence characteristics In commercial polymers are given In Table 11. The effect of additives is Illustrated In Figure 35, from which it can be seen that addition of titanium dioxide to Nylon-66 Introduces a new excitation band in the phosphorescence excitation spectrum (136). 

Fragalia and co-workers have reported the details of the He(I) and He(II) excited photoelectron spectra of Cp2Ti(CO)2 and concluded that evidence exists for significant backbonding between the Ti 3d orbitals and empty carbonyl v orbitals. Further, there is no evidence of important overlap between Ti and Cp orbitals. A small electrostatic perturbation of the Cp ligands is caused by the titanium atom (85). Bohm has described an elaborate study of the low energy PE spectrum of Cp2Ti(CO)2 (1) by means of semiempirical MO calculations (86). 

Because of the high sensitivity of Ti-containing luminescence centers to their local environments, photoluminescence spectroscopy can be applied to discriminate between various kinds of tetrahedral or near-tetrahedral titanium sites, such as perfectly closed Ti(OSi)4 and defective open Ti(OSi)3(OH) units. Lamberti et al. (49) reported an emission spectrum of TS-1 with a dominant band at 495 nm, with a shoulder at 430 nm when the sample was excited at 250 nm. When the excitation wavelength was 300 nm, the emission spectrum was characterized by a dominant band at 430 nm with a shoulder at 495 nm. These spectra and their dependence on the excitation wavelength clearly indicate the presence of two slightly different families of luminescent Ti species, which differ in their local environments, in agreement with EXAFS measurements carried out on the same samples. 

As shown in Fig. 29, highly dispersed titanium oxide anchored onto Vycor glass exhibits a photoluminescence spectrum that has a peak near 485 nm when excited by U V light at about 300 nm this is attributed to the radiative deactivation of the charge-transfer excited state of the titanium oxide species 168, 212) ... 

As shown in Fig. 65, titanium-silicon binary oxides prepared by the sol-gel method exhibit a characteristic photoluminescence spectrum near 480 nm upon excitation at 280 nm. The absorption and photoluminescence spectra are attributed to the charge-transfer processes on the highly dispersed tetrahedral titanium oxide species embedded in the Si02 matrices (168, 200, 201). When the titanium content of the oxides was decreased, the intensity of the photoluminescence spectrum increased, and its peak wavelength shifted to shorter wavelengths. 

Fig. 66. Photoluminescence spectrum of cx-titanium oxidc/Y zeolite catalyst (a) and effect of the addition of CO2 and H2O on the photolumincscence spectrum (b-d). Amount of added CO2 b, 8.5 amount of H2O c, 2.9 mmol g - measured at 77 K excitation at 290 nm emission monitored at 490 nm) [reproduced with permission from Anpo et at.

Most organometallic EDA complexes of arenes with titanium tetrachloride [116] in solution also follow the general reaction scheme in Eq. 15 in that no net chemical reaction is observed upon charge-transfer irradiation due to rapid back electron transfer (A et 10 ° s ). For example, the transient absorption spectrum of bro-moanthracene (BrAnt) cation radical generated by 532-nm laser excitation of the [BrAnt, TiCU] complex in cyclohexane (see Figure 7) decays completely to the spectral baseline within about 1 ns (see inset) due to back electron transfer [116], (Eq. 18) ... 

Transient terahertz spectroscopy Time-resolved terahertz (THz) spectroscopy (TRTS) has been used to measure the transient photoconductivity of injected electrons in dye-sensitised titanium oxide with subpicosecond time resolution (Beard et al, 2002 Turner et al, 2002). Terahertz probes cover the far-infrared (10-600 cm or 0.3-20 THz) region of the spectrum and measure frequency-dependent photoconductivity. The sample is excited by an ultrafast optical pulse to initiate electron injection and subsequently probed with a THz pulse. In many THz detection schemes, the time-dependent electric field 6 f) of the THz probe pulse is measured by free-space electro-optic sampling (Beard et al, 2002). Both the amplitude and the phase of the electric field can be determined, from which the complex conductivity of the injected electrons can be obtained. Fitting the complex conductivity allows the determination of carrier concentration and mobility. The time evolution of these quantities can be determined by varying the delay time between the optical pump and THz probe pulses. The advantage of this technique is that it provides detailed information on the dynamics of the injected electrons in the semiconductor and complements the time-resolved fluorescence and transient absorption techniques, which often focus on the dynamics of the adsorbates. A similar technique, time-resolved microwave conductivity, has been used to study injection kinetics in dye-sensitised nanocrystalline thin films (Fessenden and Kamat, 1995). However, its time resolution is limited to longer than 1 ns. 

Lasers can be classified as either continuous or pulsed sources, depending on whether their light output is steady or intermittent. This operational difference is dependent on the nature of the pump source, as a continuous excitation source will result in a continuous output beam, and a pulsed source yields a pulsed beam. Both have advantages for particular experiments. Continuous output is useful in Raman speetroseopy, for example, but pulsed lasers can be used in experiments involving short-lived speeies as deseribed in Section 2.8.1. Another operational difference is that some lasers are tunable, so they ean be used in a conventional way to scan a spectrum, whereas others are limited to a narrow frequency range. The titanium-doped sapphire laser is an example of a highly tunable infrared laser, commonly used in vibrational spectroscopy. The low-cost gas lasers tend to operate at a fixed frequency, but with superb resolution (<3 GHz), exactly what is needed for Raman spectroscopy. Semi-conductor (also known as diode) and... 

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