Best way to calculate UV-Vis absorption onset?

In summary, methods for determining the onset of a UV-Vis spectrum include plotting wavelength vs. (wavelength*Absorbance)^2 and fitting through the linear portion of the graph or calculating the first derivative and checking the zero point after the last saddle point. Tauc plots are also commonly used for this purpose.
  • #1
Dan Zar
9
0

Homework Statement


Hello,
I have a bunch of UV-Vis spectra to analyze and I am having a hard time choosing what the "onset" of each spectrum is, which I will use to calculate the optical band gap of each spectrum.

Homework Equations

The Attempt at a Solution


I read somewhere that plotting wavelength vs. (wavelength*Absorbance)^2 and then fitting through the linear portion of the graph, where the intercept corresponds to the onset.
By calculating the first derivative and checking the zero point after the last saddle point could also yield the onset? thanks
 
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  • #2
Dan Zar said:

Homework Statement


Hello,
I have a bunch of UV-Vis spectra to analyze and I am having a hard time choosing what the "onset" of each spectrum is, which I will use to calculate the optical band gap of each spectrum.

Homework Equations

The Attempt at a Solution


I read somewhere that plotting wavelength vs. (wavelength*Absorbance)^2 and then fitting through the linear portion of the graph, where the intercept corresponds to the onset.
By calculating the first derivative and checking the zero point after the last saddle point could also yield the onset? thanks
Tauc plots are typically used.
 

1. What is UV-Vis absorption onset and why is it important?

UV-Vis absorption onset refers to the point at which a sample begins to absorb light in the UV-Vis region of the electromagnetic spectrum. This is important because it can provide information about the electronic structure and properties of the sample, which can be useful for a variety of applications in fields such as materials science, chemistry, and biochemistry.

2. What is the best method for calculating UV-Vis absorption onset?

The best method for calculating UV-Vis absorption onset depends on the specific sample and the type of information needed. Generally, the most accurate method involves measuring the absorbance spectrum of the sample and identifying the onset point where the absorption curve begins to rise. This can be done using a spectrophotometer or other specialized equipment.

3. How does sample preparation affect the calculation of UV-Vis absorption onset?

Sample preparation can have a significant impact on the calculation of UV-Vis absorption onset. It is important to ensure that the sample is properly diluted and free of impurities that could interfere with the measurement. Additionally, the type of solvent used can affect the absorption spectrum, so it is important to use a solvent that is appropriate for the sample being studied.

4. Can UV-Vis absorption onset be used to determine the concentration of a sample?

While UV-Vis absorption onset can provide information about the electronic properties of a sample, it is not a reliable method for determining the concentration. Other techniques, such as UV-Vis spectroscopy combined with Beer-Lambert law calculations, are more suitable for determining the concentration of a sample.

5. Are there any limitations or potential sources of error when calculating UV-Vis absorption onset?

Yes, there are several limitations and potential sources of error that can affect the calculation of UV-Vis absorption onset. These can include instrument calibration, sample preparation errors, and interference from impurities or other substances in the sample. It is important to carefully control these factors and perform multiple measurements to ensure the accuracy of the results.

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