what material you thinking of? how do you know that it has two band gap?

Hi Mr. Hadi

Thanks for quick reply... 

The material name is Ag2MoO4. For this material in UV-Vis DRS spectrumi have observed that two maximum absorption at wavelength 330 nm and 420 nm. 

Mr. Dhanabhal

Probably, you have got a mixture of Ag nanoparticles and MoO in the product. It is well known  that  Ag nanoparticles shows maximum absorbance around 420 nm due to Surface Plasmon Resonance (SPR). Also, the band gap of MoO is higher than 3.5 eV . Thus, its maximum absorbance could be around 330 nm.

So, please verify this by conducting XRD analysis of your product to identify the presence of Ag NPs or MoO.

This can depend on the structure of the film, and may depend on the concentration of particles.

is that a nanoparticle? or a bulk film?

This is like Nanoparticle.... The size around 40 nm.

Mr. Priyesh 

I have taken XRD in that have identified the presence of only pure phase of Ag2MoO4 not other....i have not get any other phase like as you said pure Ag and MoO 

Are you familiar with these two papers?

http://pubs.acs.org/doi/full/10.1021/ic500335x

http://pubs.acs.org/doi/full/10.1021/acs.cgd.5b00455

have you read them? have you found your answer there?

Hi Hadi

I am reading now that papers

It is possible that the sample analysis relate the samples with different size nanoparticles (and the same material). Nanoparticles with the smaller size have the larger band gap (smaller absorption wavelength or Higher absorption frequency).

Dear Ali,

That is right but only for nanoparticles small enough to go under quantum confinement regime. These are 40nm sizes. still very huge for that.

It is NOT possible for a material to have 2 band gaps at the same time. Two absorption features is possible, but most probably the lower energy absorption could be caused by band-edge absorption, and the second feature could be due to an additional dopant state. But this really depends on the exact material system, so it is difficult to comment with the information you have provided.

It may be due the defects site, they can generate the energy levels below the conduction level.

may be due to exciton formation