Diffuse reflectance spectroscopy integrating spheres

Diffuse Reflectance Spectroscopy Using Integrating Spheres... 

Fig. 1 Accessories for diffuse reflectance spectroscopy (A) Integrating sphere with hemispherical radiation collection (B) Accessory based on ellipsoidal mirrors, used within the sample compartment of the spectrometer (C) Rotational ellipsoidal mirror device with dedicated detector and (D) Bifurcated fiber optic-based accessory (also shown is the random mixture of fibers for illumination and detection compared with devices based on reflection optics the acceptance cone for radiation delivery and collection is limited and depends on the refractive indices of the core and cladding material).

Spectroscopy. FT-IR spectra were recorded on a Nicolet F-730 spectrometer equipped with an in-situ flow-cell. Electron Paramagnetic Resonance (EPR) spectra were recorded in X-band with a Bruker ESP-300 with a fE (,4 cavity. Diffuse Reflectance Spectroscopy (DRS) spectra were recorded on a Cary-5 spectrofotometer with a BaS04 integration-sphere in the UV-VIS-NIR. Molecular graphics analysis was done with Hyperchem 3.0 for Windows (Hypercube Inc.). 

If the interface is totally irregular, such as a finely ground powder, the hght is reflected more diffusely as diffuse reflectance. Reflection spectroscopy, particularly diffuse reflectance, is a widely used technique for studying sohds and surfaces. The reflected hght is collected in an integrating sphere, or some similar optical arrangement, and there is usually the facility to collect or reject the specularly or diffusely reflected components. Diffuse reflectance spectroscopy is discussed in more detail in Chap. 14. 

The nature and the distribution of different types of Fe species in calcined (C) and steamed (S) samples were investigated by means of UV-vis spectroscopy. UV-vis spectra of Fe species were monitored on UV-vis spectrometer GBS CINTRA 303 equipped with a diffuse reflectance attachment with an integrating sphere coated with BaS04 and BaS04 as a reference. The absorption intensity was expressed using the Schuster-Kubelka-Munk equation. 

Recently, Castiglioni, et al. have devised a new method, diffuse reflectance CD (DRCD), to measure the solid-state CD of a pure microcrystallite sample or one mixed with KBr [42,43] and checked their performance. An integrating sphere used for UV-Vis and IR spectroscopy was introduced (Fig. 6). The advantage of this technique is to remove possible artifact elements such as reactions with the KBr, the effect of pressure required for the pellet preparation, or sample dissolution in nujol. Further, samples can be recovered after the spectral measurement, in contrast to both KBr pellet and nujol mull methods. 

Various accessories were designed for recording diffuse reflectance spectra. Apart from special devices developed by different groups and described in the literature, several commercially available types must be noted. A few accessories are shown schematically in Fig. 1, which are representative of the diversity of optics. For a long time, integrating spheres have been in use, in particular for UV/VIS and near-infrared spectroscopy, although a few applications with sensitive MCT detectors also can be found within the mid-infrared. Usually, a baffle is placed within the sphere... 

---