The band gap varies with the composition from 1.6 eV for CuO to 2.3 eV for Cu2O.

In order to measure the bandgap optically, you should first determine the fluorescence, when you excite it with photons that have an energy higher than the maximum possible bandgap, i.e > 2.3 eV.(or 1,6 eV)

This means you must use a strong source with a wavelength < 1240/2.3 = 540nm

A good source is a 254 nm mercury lamp, that has a high intensity and a photon energy of 1240/254= 4.9 eV, so high enough.

You will then find all the emission peaks with wavelengths in the visible and the near infrared (NIR). Use a solid state detector/spectrometer (e.g an AVANTES) to find the IR emission peaks

An alternative excitation source is to use your UV-VIS monochromator/spectrometer.

You select the monochromator at a wavelength shorter than 540nm

Then you determine the VIS/IR emission peaks from your copper-oxide nanotubes.

The next step is to find out at which energies these emission peaks are optimally excited; i.e the excitation spectrum. To do this you must change the wavelength and scan from say 400nm down to 900nm.

The difficulty is that if we assume that the bandgap is really 1.6 eV, then the excitation at the bandgap (exciton formation) really occurs around 1240/1.6= 775nm.

So your lamp (source) should have a strong emission around that wavelength.

Furthermore, your detector inside your spectrometer should be sensitive down to at least 900nm. In general the standard spectrometers (photo-multiplier tubes) cannot detect this wavelength range

But you can use a silicon solid state detector inside your spectrometer. Silicon has a bandgap at 1100nm, so that you can detect optimally around 900nm.

You the use such a spectrometer in combination with a commercial monochromator

Good luck,

Harm Tolner, Eindhoven, the Netherlands

to work out the bandgap you should find the cutoff point of the curve and x axis then devide with a constant

The band gap varies with the composition from 1.6 eV for CuO to 2.3 eV for Cu2O.

In order to measure the bandgap optically, you should first determine the fluorescence, when you excite it with photons that have an energy higher than the maximum possible bandgap, i.e > 2.3 eV.(or 1,6 eV)

This means you must use a strong source with a wavelength < 1240/2.3 = 540nm

A good source is a 254 nm mercury lamp, that has a high intensity and a photon energy of 1240/254= 4.9 eV, so high enough.

You will then find all the emission peaks with wavelengths in the visible and the near infrared (NIR). Use a solid state detector/spectrometer (e.g an AVANTES) to find the IR emission peaks

An alternative excitation source is to use your UV-VIS monochromator/spectrometer.

You select the monochromator at a wavelength shorter than 540nm

Then you determine the VIS/IR emission peaks from your copper-oxide nanotubes.

The next step is to find out at which energies these emission peaks are optimally excited; i.e the excitation spectrum. To do this you must change the wavelength and scan from say 400nm down to 900nm.

The difficulty is that if we assume that the bandgap is really 1.6 eV, then the excitation at the bandgap (exciton formation) really occurs around 1240/1.6= 775nm.

So your lamp (source) should have a strong emission around that wavelength.

Furthermore, your detector inside your spectrometer should be sensitive down to at least 900nm. In general the standard spectrometers (photo-multiplier tubes) cannot detect this wavelength range

But you can use a silicon solid state detector inside your spectrometer. Silicon has a bandgap at 1100nm, so that you can detect optimally around 900nm.

You the use such a spectrometer in combination with a commercial monochromator

Good luck,

Harm Tolner, Eindhoven, the Netherlands

Dear Shi Tang, thanks for the info but i am asking whether it is possible to get absorbance spectra of CuO nanotube thin film deposited on Cu substrate. or do i need to scratch it and make powder and then using solvent, find absorbance????

Krishna,

You may attempt to measure of reflectance spetcra of CuO and then refer the following research article may provide the information on how to use reflec. data to determine the band gap.

http://www.sciencedirect.com/science/article/pii/S0927024807001948

Best wishes,

Malkesh

Thanks Mr. Malkesh ! :-)

Calculo de band-gap por métodos opticos

Here you can find good explanation and band gap calculator,

http://www.instanano.com/characterization/theoretical/uv-vis-spectroscopy-band-gap-calculation/