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Catalytic Surfaces and Catalyst Characterization Methods
Published in James J. Carberry, Arvind Varma, Chemical Reaction and Reactor Engineering, 2020
W. Nicholas Delgass, Eduardo E. Wolf
Reflectance techniques have been used with opaque samples that do not permit transmission. Specular reflection has been used in the case of metal mirrors such as single crystals or foils and, in principle, provides an attractive combination with other spectroscopic techniques involving flat surfaces. Diffuse reflectance spectroscopy (DRS) is used when the reflecting surface is rough and the incident radiation is reflected (scattered) diffusely. Such radiation must be collected by a hemispherical or elliptical reflector and focused into the detector. Klier (1980) summarizes the literature, theory, and application of DRS to the study of adsorbed species on catalysts.
4 Host Lattice
Published in Vikas Dubey, Sudipta Som, Vijay Kumar, Luminescent Materials in Display and Biomedical Applications, 2020
Ramachandra Naik, S.C. Prashantha, H. Nagabhushana, Yashwanth V. Naik, K.M. Girish, H.B. Premkumar, D.M. Jnaneshwara
The measurement of diffused radiation reflected from a surface constitutes the area of spectroscopy known as diffuse reflectance spectroscopy. Diffuse reflectance spectrometry concerns one of the two components of reflected radiation from an irradiated sample, namely specular reflected radiation, Rs and diffusely reflected radiation, Rd. The former component is due to the reflection at the surface of single crystallites while the latter arises from the radiation penetrating into the interior of the solid and re-emerging to the surface after being scattered numerous times. These spectra can exhibit both absorbance and reflectance features due to contributions from transmission, internal and specular reflectance components as well as the scattering phenomenon in the collected radiation. Diffuse Reflectance Spectra (DRS) of doped samples were recorded and analyzed its absorption peaks. It was observed in different doped samples that different peaks were present which are attributed to characteristic transitions of dopant ions. In Eu3+ doped samples, the bands observed in the DR spectra at ~393 and ~464 nm were attributed to the intra configurationally 4f–4f transitions from the ground7F0 level. The Tb3+ doped samples show peaks at 323 nm and 390 nm which confirms that absorption takes place at these particular wavelengths. The DR spectra of Sm3+ doped Mg2SiO4 nanophosphors shows a strong absorption band in the shorter wavelength range 200–300 nm (i.e. higher energy) for all samples may be ascribed to the absorption of the host lattice. When Sm3+ ions is introduced into the host lattices, several weak absorption bands in the larger wavelength range 300–480 nm (i.e. low energy) are observed. These electronic bands are the characteristics of Sm3+ ions, starting from the ground state6H5/2 to the various excited states of Sm3+ ions. In Dy3+ doped Mg2SiO4 nanophosphors DR spectra show a strong absorption bands at 320, 350 and 390 nm which are attributed to Dy3+ ions (Kumar et al. 2014).
Polymer-mediated electrospun nanofibrous mats on supramolecular assembly of nortriptyline in the β-cyclodextrin medium for antibacterial study
Published in Journal of Biomaterials Science, Polymer Edition, 2022
Rajaram Rajamohan, Angaiah Subramania, Yong Rok Lee
From the ultraviolet to the mid-infrared spectral region, diffuse reflectance spectroscopy is widely used. However, diffuse reflectance spectroscopy can be used to characterize any sample that scatters radiation. In Figure 5, the diffuse reflectance spectra of NP/PAN and NP:β-CD-IC/PAN NFMs are shown. There was a total transmittance and diffuse reflectance of about 15% in the visible range at lower wavelengths in both spectra. The difference in the transmittance between NP:β-CD-ICs/PAN NFMs (Figure 4b) and NP/PAN NFMs (Figure 4a) can logically be attributed to some supramolecular interaction between NP and β-CD.
Fluorescence and diffuse reflectance provide similar accuracy in recovering fluorophore concentration at short source-detector separations
Published in Journal of Modern Optics, 2022
Jacob R. Roccabruna, Karina G. Bridger, Timothy M. Baran
Fluorescence and diffuse reflectance both offer advantages and disadvantages for the determination of the concentration of fluorescent compounds. Fluorescence measurements have a more identifiable ‘fingerprint,’ as the shape of the fluorescence emission spectrum is known a priori. In fact, this knowledge of spectral shape has been exploited to recover fluorophore concentration without corresponding reflectance measurements [16,17], although applicability is limited to specific geometries and background optical properties. This can result in fluorescence measurements being more accurate at low concentrations, though we did not observe this at the concentrations examined in the present study. Further, diffuse reflectance requires measurable attenuation of the illumination source by fluorophore absorption in order to recover fluorophore concentration. Here, we have used MB as the fluorophore, as this is the photosensitizer we employ in our ongoing Phase 1 clinical trial of PDT for deep tissue abscesses. MB has a relatively high- extinction coefficient of approximately 74,021 cm−1/M [18]. On the other hand, native fluorophores such as collagen have lower extinction coefficients and are generally excited at UV wavelengths [19,20]. Fluorescence may therefore be better suited for recovery of the concentration of these lower extinction fluorophores, as well as for low fluorophore concentrations. Diffuse reflectance spectroscopy can utilize a significantly simpler optical design, as laser excitation and emission filtering are not required. Many fluorescence systems also require additional switching optics to accommodate excitation sources and filters [21–23], which increases cost and complexity. The decision of whether to add fluorescence measurements to a diffuse reflectance spectroscopy system should therefore be guided by the fluorophores of interest, and investigators should consider whether these fluorescence measurements are necessary for the desired application.