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vinhphysics
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The absorption spectra of some materials appear as the absorption bands (for example: TiO2 powder) while the other appear as the absorption peaks (for example: Quantum dots). Please explain why they are different?
I don't think you are using the word "band" correctly. A "band" can have a maximum.vinhphysics said:The peaks means we can find some maximum points on the spectrum (See absorption spectrum in link: http://www.viewsfromscience.com/documents/webpages/nanocrystals.html ). The Band means no maximum points can be found on the spectrum (See absorption spectrum in link: http://www.springerimages.com/Images/RSS/1-10.1007_s13204-011-0005-4-3)
vinhphysics said:Thank you Darwin123 for your discussions.
May be I had a mistake in using the scientific terms. What I want to say is some materials absorb all photons which their energy are higher than the band gap of material while some materials absorb strongly the photons which have certain energy. This means if the photons energy are higher than the certain energy (and band gap), the materials absorb lesser
I have seen the word "shoulder" used for "thresholds". The words have slightly different meanings, but often refer to the same type of features. A shoulder is usually a change in the derivative of a spectral function without a change in sign. A threshold usually refers to an sudden increase in the value of a function without a concomitant drop.vinhphysics said:The absorption spectra of some materials appear as the absorption bands (for example: TiO2 powder) while the other appear as the absorption peaks (for example: Quantum dots). Please explain why they are different?
An absorption band refers to a range of wavelengths in the electromagnetic spectrum where a substance absorbs light. This results in a decrease in the intensity of light passing through the substance. The absorption band is typically displayed as a graph, with the x-axis representing the wavelength and the y-axis representing the degree of absorption.
An absorption band is caused by the interaction between light and matter. When light of a specific wavelength passes through a substance, the energy of the light is transferred to the molecules of the substance. This causes the electrons in the molecules to become excited and move to higher energy levels, resulting in the absorption of the light.
An absorption peak is the highest point on an absorption band graph, representing the wavelength at which the substance absorbs the most light. It is the peak of the curve on the graph and indicates the specific wavelength at which the substance has the highest degree of absorption.
An absorption band is typically measured using a spectrophotometer, which measures the amount of light absorbed by a substance at different wavelengths. The substance is placed in a cuvette and a beam of light of varying wavelengths is passed through it. The spectrophotometer then measures the amount of light that passes through the substance, allowing for the creation of an absorption band graph.
An absorption band can provide valuable information about the properties of a substance. By analyzing the shape and intensity of the absorption band, scientists can determine the chemical composition, concentration, and purity of a substance. It can also be used to study the physical state of a substance, such as its temperature and pressure, and to identify unknown substances by comparing their absorption bands to known substances.