Use and misuse of the Kubelka-Munk function to obtain the band gap energy from diffuse reflectance measurements

Landi, Salmon; Segundo, Iran Rocha; Freitas, Elisabete F.; Vasilevskiy, Mikhail; Carneiro, Joaquim A. O.; Tavares, C. J.

doi:10.1016/j.ssc.2021.114573

Cited by 247 publications

(95 citation statements)

References 47 publications

(53 reference statements)

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“…The experimental band gaps of EuLnCuSe 3 were determined from the Kubelka-Munk functions (Figure S4 in the Supplementary Materials). A recent study suggested that use of the simple Kubelka-Munk function may lead to errors in band gap values of the order of several tenths of eV [77]. Landi et al argue that the Tauc-type modification of the Kubelka-Munk functions, though containing approximations, leads to more correct band gap values.…”

Section: Band Structure and Optical Properitesmentioning

confidence: 99%

Quaternary Selenides EuLnCuSe3: Synthesis, Structures, Properties and In Silico Studies

Grigoriev

Solovyov

Русейкина

et al. 2022

IJMS

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In this work, we report on the synthesis, in-depth crystal structure studies as well as optical and magnetic properties of newly synthesized heterometallic quaternary selenides of the Eu+2Ln+3Cu+1Se3 composition. Crystal structures of the obtained compounds were refined by the derivative difference minimization (DDM) method from the powder X-ray diffraction data. The structures are found to belong to orthorhombic space groups Pnma (structure type Ba2MnS3 for EuLaCuSe3 and structure type Eu2CuS3 for EuLnCuSe3, where Ln = Sm, Gd, Tb, Dy, Ho and Y) and Cmcm (structure type KZrCuS3 for EuLnCuSe3, where Ln = Tm, Yb and Lu). Space groups Pnma and Cmcm were delimited based on the tolerance factor t’, and vibrational spectroscopy additionally confirmed the formation of three structural types. With a decrease in the ionic radius of Ln3+ in the reported structures, the distortion of the (LnCuSe3) layers decreases, and a gradual formation of the more symmetric structure occurs in the sequence Ba2MnS3 → Eu2CuS3 → KZrCuS3. According to magnetic studies, compounds EuLnCuSe3 (Ln = Tb, Dy, Ho and Tm) each exhibit ferrimagnetic properties with transition temperatures ranging from 4.7 to 6.3 K. A negative magnetization effect is observed for compound EuHoCuSe3 at temperatures below 4.8 K. The magnetic properties of the discussed selenides and isostructural sulfides were compared. The direct optical band gaps for EuLnCuSe3, subtracted from the corresponding diffuse reflectance spectra, were found to be 1.87–2.09 eV. Deviation between experimental and calculated band gaps is ascribed to lower d states of Eu2+ in the crystal field of EuLnCuSe3, while anomalous narrowing of the band gap of EuYbCuSe3 is explained by the low-lying charge-transfer state. Ab initio calculations of the crystal structures, elastic properties and phonon spectra of the reported compounds were performed.

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Section: Band Structure and Optical Properitesmentioning

confidence: 99%

Quaternary Selenides EuLnCuSe3: Synthesis, Structures, Properties and In Silico Studies

Grigoriev

Solovyov

Русейкина

et al. 2022

IJMS

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“…The absorption edge shifts to the visible spectral region when the MW-assisted process is employed for the synthesis; no effects due to silver incorporation into the TiO 2 are observed. The corresponding optical bandgaps (Eg) were determined using the Tauc method; this was conducted by transforming the reflectance spectra to the Kubelka–Munk function, F(R), and then plotting (F(R)∙E) 2 versus E [ 64 ]. The bandgap values were obtained by a linear fit of the linear portion of the curve, determining its intersection with the photon energy axis.…”

Section: Resultsmentioning

confidence: 99%

“…Raman measurements were performed using a micro-Raman LabRam 800 system, equipped with a confocal microscope Olympus BX40 and a 100Χ objective; the samples were excited using the second harmonic of an Nd:YAG laser (532 nm). Diffuse reflectance measurements (DRS) were conducted in a Perkin Elmer Lambda 35 UV–Vis spectrophotometer to obtain the bandgap values through the Kubelka–Munk function [ 64 ]. The XPS spectra were acquired in the low- and high-resolution regimes with a K-alpha Thermo Scientific (Waltham, MA, USA) XPS spectrometer.…”

Section: Methodsmentioning

confidence: 99%

Green Synthesis via Eucalyptus globulus L. Extract of Ag-TiO2 Catalyst: Antimicrobial Activity Evaluation toward Water Disinfection Process

et al. 2022

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The problem of water pollution by persistent substances and microorganisms requires solutions that materials such as silver-modified titanium dioxide can provide due to their excellent photocatalytic and antimicrobial properties. However, the synthesis methods conventionally used to obtain these materials involve toxic chemical reagents such as sodium borohydride (NaBH4). The search for alternative synthesis methods that use environmentally friendly substances, such as the biosynthesis method, was evaluated. Silver-titanium dioxide (Ag-TiO2) was synthesized by a Eucalyptus globulus L. extract as a reductive agent through sol-gel and microwave-assisted sol-gel processes. Four different solvents were tested to extract secondary metabolites to determine their roles in reducing silver nanoparticles. Titanium dioxide nanoparticles with sizes from 11 to 14 nm were obtained in the anatase phase, and no narrowing of the bandgap was observed (3.1–3.2 eV) for the Ag-TiO2 materials compared with the pure TiO2. Interestingly, the bacterial inhibition values were close to 100%, suggesting an effective antimicrobial mechanism related to the properties of silver. Finally, by the physicochemical characterization of the materials and their antimicrobial properties, it was possible to obtain a suitable biosynthesized Ag-TiO2 material as a green option for water disinfection that may be compared to the conventional methods.

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“…In our measurements, the sample was analyzed through diffuse reflectance arrangement. Figure 6 shows the absorption spectra of the as-prepared NiO samples (i.e., N-1, N-2, and N-3) transformed from the diffuse reflection spectra according to the Kubelka-Munk (K-M) theory [40]. The energy bandgap of NiO particles could be estimated from the Eg measurement using Kubelka-Munk functions [41] and F(R) is estimated from the following equation:…”

Section: Optical Propertiesmentioning

confidence: 99%

Calcination Temperature Reflected Structural, Optical and Magnetic Properties of Nickel Oxide

et al. 2022

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Stoichiometric compositions of NiO were prepared by the standard chemical co-precipitation method to inspect the effect of the calcination temperature on structures, morphology, and physical properties. The samples were calcined at three different temperatures viz. 350 °C, 550 °C, and 650 °C for 5 h. X-ray diffraction analysis confirmed the cubic (Fm-3m) structure of the prepared samples. The average crystalline size increases from 41 nm to above 100 nm as the calcination temperature increases in the same time period. In Fourier transform infrared spectra, the spectral absorption bands were observed at ~413, 434, and 444 cm–1. The bandgap energy of NiO particles is decreased from 3.6 eV to 3.41 eV as the calcination temperature increases. The magnetic analysis confirms that the magnetization value of NiO is invariably decreased with a rise in the calcination temperature.

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Use and misuse of the Kubelka-Munk function to obtain the band gap energy from diffuse reflectance measurements

Cited by 247 publications

References 47 publications

Quaternary Selenides EuLnCuSe3: Synthesis, Structures, Properties and In Silico Studies

Quaternary Selenides EuLnCuSe3: Synthesis, Structures, Properties and In Silico Studies

Green Synthesis via Eucalyptus globulus L. Extract of Ag-TiO2 Catalyst: Antimicrobial Activity Evaluation toward Water Disinfection Process

Calcination Temperature Reflected Structural, Optical and Magnetic Properties of Nickel Oxide

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