# How to calculate the particle size of quantum dots from UV-Vis spectrum.

Can anyone help me?

Question

Can anyone help me?

- Sorry I don't know such kinds of methods to analyze particle of GQs. I don't understand why you are thinking about UV-vis instead of DLS/ELS or TEM/SEM?

However, just one idea knocked in my head. Most probably it does work. First get a standard curve based on excitation wavelength VS particle size of different QDs (blue,green, yellow,red). Then you can take UV spectrum of your unknown QDs. From the standard curve you may a get particle size data (it may not appropriate, i assume).

As you know there is a direct relation between excitation wavelength and particle size of QDs. However, before doing this try to find some reference either exist or not.

Thanks - dear sir

thanks for your valuable suggestion. In some papers, they had calculated the particle size using Brus equation in terms of bandgap of energy (Eg), effective mass of excitons (electron and hole pair). Is effective mass of exciton for all materials same? - Use Brus equation for calculating the particle size...
- Joicy, its not a good idea to calculate exact particles size from UV-vis, you can get an idea about size distribution depends on nature of the curve and the position of the peak. if you have narrow peak you have uniform size distribution and if you have broad peak your sample is not uniform or some case different shapes.
- thank you Mr.Angshuman pal for your suggestion.
- Joicy : Sizes of nanoparticles may be determined using the photoluminescence spectra as it presented in our paper. It is possible if you observe structure in the photoluminescence spectra.
- Effective mass of exciton is a characteristic of semiconductor material.

See paper, which attached. - Thank you professor Yu. Gnatenko for your suggestions.
- Hi Joicy, as in your other question, you have two options:

The Brus model (theoretical model based on quantum mechanics, known as the effective mass approximation)

or

An empirical relationship, if it has been previously determined (e.g. Yu model for CdS quantum dots)

Based on the quantum nature of the phenomenon, the simplest relationships between the wavelength corresponding to the absorption edge and the size of the quantum dots are quadratic and cubic functions.

Also, the theoretical model considers only particles with a specific diameter (monodisperse), while an empirical model assumes that the particle diameter is the average diameter of the actually particle size distribution (polydisperse). - Thanks to all they give a valuable suggestion.
- Joicy, Below is attached my paper where I have used UV data for size calculation. It might belp you
- Particle Size Calculation from UV-Vis.

For metal nanoparticles, size can be calculated from FWHM of SPR peak using equation

FWHM = 50 + 2300 / D.

FWHM (Full Width Half Maximum) and D-particle diameter is in angstroms [Ind. Eng. Chem. Res., 39, (2000), pp. 4749-4755].

For semiconductor nanoparticles, size can be calculated from bandgap. For details refer: Res.Appl.Mat.07/2013; 1(4):36. DOI:10.12966/ram.07.02.2013); - It is not good idea to calculate particles size from UV-vis,better to do that through TEM
- There are different sizing curve equations are given by different researchers to calculate the size of the quantum dot. For instance, this is a paper where you can calculate the size of the Cd(S, Se, Te) quantum dots. It would be nice if you can specify your QDs.
- Also, you can say the effective mass for electron and hole for a particular semiconductor as its characteristic property. Though effective masses vary with curvature of band shape.

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