Dear Siyamak Shahab thank you for the reply,but for everytime I repeated getting the negative value for the starting wavelenghts

Dear Pradeep,

Siyamak Shahab is right. Negative absorbance values indicate clearly that your experiment is flawed because of improper method of measuring absorption spectra. Will you kindly describe in detail your experimental setup and protocol. Then somebody of our community might be able to help you.

Best regards

Mirek

Dear Jaromir ,

 I have sent you the message personally about the protocol I have followed and thank you for the reply

Dear Pradeep,

Thank you for your message. However,  your protocol to prepare materials to be tested is unlikely to cause negative absorbances. I need to learn more information about your spectrometer.

1. Spectrometer model

2. Method used ( single or double beam?)

3. What is the extent of light scattering by your samples?

Best regards

Mirek

Dear plasek,

model is-UV-Vis-NIR-3600 plus shimadzu

It is doble beam

And what is meant by extent of light scattering by my samples?

thank you

Are your samples turbid?

Dear Pardeep,

It is better to display a curve of absorbance versus the wavelength rather than supply your data in excel sheet.

Would you please define the absorbance as you measured it. It seems me  that the peaks may be due to the change of reflection with the wavelength.

This is a preliminary thoughts before one gets answers on the previous questions.

wish you success

Dear Olasek,

 My samples are not in turbid nature,they are easily dispersable.

Dear Zerkhy,

As you asked I am attaching my graph see once

Even if your samples do not appear turbid to the naked eye, a suspension of nanoparticles often scatter light and this phenomenon is most egregious in the UV region.  Although you are using a quality double beam spectrophotometer, the photomultiplier detector cannot detect light that is being scattered in all directions due to the reflective surfaces of the nanoparticles in your sample.  The light which is scattered away from the PMT is not detected and, therefore, the instrument returns a negative absorbance value which is an incorrect answer.  The use of an integrating sphere will help to capture the scattered photons and provide a more accurate spectral shape, however an exact absorbance calculation cannot be obtained because the pathlength in an integrating sphere is not known.  To obtain accurate abs/cm-1, an integrating cavity with a pathlength that can be calculated must be used.

 See:  Quantitative spectrophotometry using integrating cavities

Javorfi, T., Erostyak, J., Gal, J., Buzady, A., Menczel, L., Garab, G., Naqvi, K. R., Journal of Photochemistry & Photobiology, B: Biology, 82, 127 (2006).

and other publications listed at:  http://www.olisclarity.com/#!pre-clarity-publications/c1bai

The absorption curve you have is the resultant of the absorption of the two layers, the SnO2 and the ZnO. every material has its own absorption peak as apparent from the attached links:http://www.sbcollege.org/support/AR/AR%20061.pdf

and http://www.nature.com/articles/srep20878

best wishes

thank you kristi and zekry for the suggestions