We knew A = -log T, however, for a concrete question, such as with increased CdSe particle sizes how to explain change of absorption peaks of UV-visible spectra, what is the relationship among position of absorption peaks, wavelength and particle size? what is their significance of every absorption peaks (stronger peaks) from UV-visible spectrum?
Not sure if this is what you are looking for...
http://nanocluster.mit.edu/wiki/images/f/f2/Synthesis_fig2.jpg
Its related with quantum confinement, when reduce the size of semiconductor CdSe in nanometric level have increased your bandgap, absorbs higher energy or lower wavelength.
Of course both absorption and emission spectra change with size, as soon as your particle size crosses the Exciton-Bohr-Radius of the material (which is when you start observing quantum confinement), as Johan and Il already pointed out. Your energy levels discretize and move higher up in the bands for stronger quantum confinement (smaller size). The figure Alejandro posted shows this change in absorption for different sizes nicely. You can expect the emission peak in approximately the position of the first absorption peak, just a bit shifted to lower energy (Stokes-shift).
Benjamin resume the question very well, the effect occurs for size smaller than the Exciton-Bohr-Radius of the material and lL Jeong it's right too.
both absorption and emission spectra change with size .the absorption and emission energy peak decrease by increasing the size, and so the wavelength of absorption and emission peak increases when the size increases.
Dr. Benjamin has answered the question very easily. As the size of the dots increases it experiences less confinement, as a result band gap of the material diminishes. That means it exhibits less quantum effect. Consequently it absorbs energy with higher wavelength. Thats why absorption spectra shifts to lower energy (higher wavelength) regime as the size of dots increases.
I think That there is an inverse relation between particle size and energy gap so when the particle size increase , the absorption peaks will shift toward longer wavelength and virse versa
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