Integrating sphere spectrometer

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. 

Fig. 1 Schematic diagram of the integrating sphere portion of a diffuse reflectance spectrometer, illustrating the key elements of the optical train. Although the detecto has been placed in the plane of the sample and reference materials, in common practice it would be mounted orthogonal to the plane created by the intersection of the optica beams.

In this section the ideal case of vanishing reabsorption, Ke = 0, is discussed, where Fb + Ff= Ftot- A large area of the sample should be irradiated close to /to = 2/3, what is a very convenient geometry in most spectrometers, or diffusely via an integrating sphere, what is less convenient but guarantees homogeneous density of irradiation. Under these conditions Eqs. (8.27) and (8.28) are sufficiently accurate for quantitative evaluation. 

UV-VIS-NIR diffuse reflectance (DR) spectra were measured using a Perkin-Elmer UV-VIS-NIR spectrometer Lambda 19 equipped with a diffuse reflectance attachment with an integrating sphere coated by BaS04. Spectra of sample in 5 mm thick silica cell were recorded in a differential mode with the parent zeolite treated at the same conditions as a reference. For details see Ref. [5], The absorption intensity was calculated from the Schuster-Kubelka-Munk equation F(R ,) = (l-R< )2/2Roo, where R is the diffuse reflectance from a semi-infinite layer and F(R00) is proportional to the absorption coefficient. 

FIGURE 8 Reflectance properties of typical white standards in the UV-vis-NIR range. (A) Reflectance of barium sulfate. The measurement was carried out with a PerkinElmer Lambda 9 spectrometer equipped with an integrating sphere, and the reactor cell described in Ref. (Thiede and Melsheimer, 2002). For the background correction one piece of Spectralon was placed at the reference port of the sphere, a second piece was placed inside the reactor cell at the sample port of the sphere. For measurement of the presented spectra, BasS04 was placed in the reactor, while the piece of Spectralon at the reference port remained in position. (B) Reflectance of Spectralon as provided by the manufacturer. 

Zou and Gonzalez (1992) published the diagram of a design that allows placement of an integrating sphere next to a quartz window in a reactor. Fiber optic cables were used as an interface between an integrating sphere and a PerkinElmer UV-vis spectrometer. The maximum temperature of the cell was stated to be 773 K, and spectra were presented for temperatures up to 473 K. 

Reference and sample measurements are performed consecutively, and the resultant (sample) spectrum is obtained as the ratio of the two photon fluxes onto the detector. In a single-beam spectrometer, there are no other options in a double-beam spectrometer, the photon fluxes of the sample and reference beam path are compared. When an integrating sphere is used with two ports and a white standard in the reference position, the photon fluxes are comparable to each other, and no problems occur. Note that the ports are part of the sphere and that any material change in the reference or sample position will change the average sphere reflectance pave. The reference measurement should be conducted with exactly the same components (windows) as the sample measurement otherwise, "substitution errors" may occur. 

For diffuse reflection analysis, it is necessary to fit the spectrometer with an integration sphere the function of which is to collect the light diffused in all directions. Although several designs have been proposed, the most commonly adopted is that of Harrick which enables... 

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.). 

The schematic setup of a diffuse reflectance spectrometer which is obtained by supplying a normal UV-VIS spectrometer with a diffuse reflectance accessory is shown in Fig. 18. The core is an integrating sphere coated with a highly reflective material that collects the scattered radiation and leads it to the detector. The light remitted by the sample is compared with that of a white standard as the reference. Zeolite layers of ca. 5 mm depth are generally sufficient to meet the condition of infinite thickness. A typical sample cell furnished with an evacuated Infrasil double window and designed for temperature control and evacuation is depicted in the lower part of Fig. 18 [32]. Other cell constructions have been reported by Klier [31] and Schoonheydt [34]. 

Fig. 18. A Schematic representation of a diffuse reflectance spectrometer. For (i) nondiffuse dispersed illumination the source at the left and the detector at the integrating sphere are used. For (ii) diffuse nondisperse illumination (in the case of fluorescent samples) a source directly attached to the sphere and the detectors on the left upper side are applied. B Temperature-regulated and evacuable diffuse reflectance sample cell according to [32]. Reprinted from [32] with permission of Academic Press, Inc...

Following the reference and dark scans, the working sample is placed against the aperture of the integrating sphere. The spectrometer then determines the amount of light reflected by the sample by comparison against the reference standard. 

The UV/vis spectra were recorded on a Perkin-Elmer Lambda 900 UV/vis spectrometer equipped with a diffuse reflectance and transmittance accessory (PELA-1000). The accessory is essentially an optical bench that includes double-beam transfer optics and a six-inch integrating sphere. Background corrections were recorded using a Labsphere SRS-99-020 standard. The reflectance data from were converted to k/s values by using the Kubelka-Munk theory (1931). The Kubelka-Munk equation describes the infinite reflectance as a function of absorption and scattering ... 

Transmission, mid-IR cw-spectra of GP were obtained by employing KBr pellets with GP powder homogenously embedded in the pellets. Reflectance NIR spectra of GP were obtained from purified powders (without KBr) on a Perkin-Elmer Spectrum ONE NTS spectrometer equipped with an integrating sphere and an extended-range InGaAs detector. 

Typical fluorescence spectrometers deliver relative fluorescence intensities They are altered by both the wavelength-dependent throughput of optical elements (lenses, mirrors, gratings, lamps) and spectral sensitivity of the detector. Often, these relative spectra are sufficient. In order to obtain corrected spectra, one may use quantum counters or integrating spheres, for instance. 

UV-Visible absorption spectra measurements in the wavelength range of 250-1050nm were performed at room temperature using a Perkin-Elmer Lambda 45 UV/VIS spectrometer equipped with an integrating sphere. These measurements were made on glass pwwder dispersed in KBr pellets. The optical absorption coefficient, a, was calculated from the absorbance. A, using the equation ... 

---