Dear Cui,

From the principle point of view band gap engineering of semiconductors is achieved by by mixing the elements to from compounds. In your case you have to add Pt atoms in the lattice of the zinc oxide to substitute the divalent atoms of zinc. The shift can be tuned by the percentage of PT introduced in the TRI element compound. 

wish you success

Hi Abdelhalim Zekry, thanks for your reply.

Yes, but because I do not actually want to tune my band gap, I just want to load Pt sa cocatalyst, so I shouldn't get any shifted peaks in my photoluminescene (PL) spectra right? But no matter how I repeat it, the peak of my PL spectrum for Pt loaded on ZnO is always shifted higher than the peak for bare ZnO. I wonder why...

What is the deposition temperature of the platinum on ZO? Is there any post heat treatment. Any relatively high temperature process, it will cause intermixing and the formation of tri element compound a the interface between the two films. I would expect that platinum atoms are bonded to the oxygen atoms at the interface. and so, PtZO mixer is formed at the interface.

wish you success 

I think you are looking e-h pair recombination /emission not band-band transition in your sample. This is only possible if you dopedal Pt in ZnO otherwise please try to focus the sample away from Pt dots! In doped case you shul see two peaks overlapping. Please perform uv-visible for confirmation!

Hi Muhammad Asghar. Thanks for your reply. I'm not doping Pt into ZnO that is why theoritically I should not get a band shift right? But i tried a few times characterizing using PL and UV-Vis. PL always show the shift on the other hand UV-Vis always show that there is not band gap differences between this two sample. Can that actually happen?

Thanks for the update, I will appreciate if you tell me the PL machine detail: excitation frequency and then I will ask for PL spectrum of the test sample supplied by the supplier!, I have question on the calibration of your machine, may be?

Dear Cui Ying,

PL is very sensitive to the material for which you are taking spectrum as compared to absorbance spectroscopy.

The small shift in PL of loaded samples may be closely related to the impact of Pt deposited on ZnO. It might originate from the distortion of the ZnO surface crystal lattice structure due to the loaded Pt. You can confirm this with Raman spectroscopy in which you will also observed shift in Raman signal as it is closely related to the environment of the material. But, if you take XRD then there will be no shift in peak position in case of loaded sample, but in case of doped samples there will be shift in XRD spectra.

Hope this will be useful to you.

Hi Ranjana Varma,

Really thanks for your suggestion and explaination. I will consider looking at the Raman =)