Dear Jubyeong Chae,

I'm not sure if you are working with metal nanoparticles but the size of the particle has a very big influence in the absorption spectrum. If you have very small particles you will have a blue shift in the spectrum. Conversely, if you have bigger nanoparticles you will have a red shift.

Joan

If these results belong to metallic nano particles the absorption band due to SPR band with increasing particle size band is red shift.

For more details please read following article: Structural and physical characteristics of Au2O3 doped sodium antimonate glasses-part I, DOI: 10.1111/jace.16013 .

Article Structural and physical characteristics of Au2O3 doped sodiu...

Red shift and blue shift describe how light shifts toward shorter or longer wavelengths. A blue shift is any decrease in wavelength, with a corresponding increase in frequency, of an electromagnetic wave; the opposite effect is referred to as red shift. Blue shifts corresponding to the absorption edge in the UV-A (310–400 nm) range are obtained from ultraviolet (UV) absorption spectra. The absorption edge red shift is observed at higher energy band >3.0 eV. The red shift in the band gap is observed due to the improved crystallinity of the thin film. The optical band gap of the film decreases with the increase in grain size. The barrier height of the grain boundary increases with the increase in grain size resulting in a decrease in the band gap of the thin film.

Dear Jubyeong Chae,

I have few suggestions, better to call them as different ways of looking at the problem

From fig.1 it is clear that, binding of metal ion to the ligand caused a blue shift and increased the emission intensity. Hence you better go through the topic “metal enhanced fluorescence” where you can find the possible mechanism.

In my opinion the absorption peak is not shifted, just a new peak (corresponding to metal ligand complex) is formed at the expense of the former one.

The new absorption and new emission peaks (i.e. blue shifted peak) are may be the characteristic features of the formed metal ligand complex.

Comparing the excitation spectra of ligand and the metal ligand complex can give you some more information.

All the best....