Dear Kumar,,

In addition to other dear researchers, It is well known that optical absorption of photocatalysts significantly influences their activity. Photoluminescence (PL) signalsand their intensity are closely related to its photocatalytic activity. Further addition of metal content of the samples reduces the PL intensities, due to shorter distance of inter band metal ions, which result in an energy transfer between nearby ions. Therefore, a concentration quenching process will occur, due to a non-radiative decay process.  However, the inherent relationships are very complicated, and can properly be disclosed only on the basis of PL attributes, closely related to dopant species. For band–band PL signals, the lower the PL intensity, the higher the separation rate of photo-induced charges and, possibly, the higher the photocatalytic activity. For excitonic PL signals, the lower the PL intensity, the higher the separation rate of photo-induced charges and, possibly, the higher the photocatalytic activity. The stronger the PL signal, the higher the content of surface oxygen vacancies and defects and possibly the higher the photocatalytic activity. Therefore, it can be suggested that the photocatalytic activity of samples can be quickly evaluated by means of PL measurements under a certain condition.

J. Liqiang, Q. Yichun, W. Baiqi, L. Shudan, J. Baojiang, Y. Libin, F. Wei, F. Honggang, S. Jiazhong, 'Review of photoluminescence performance of nano-sized semiconductor materials and its relationships with photocatalytic activity' Sol. Energy Mater. Sol. Cells, 90 (2006), pp. 1773–1787.

Good luck

http://www.sciencedirect.com/science/article/pii/S0927024805003570

During doping you are increasing the energy levels reducing the band gap simultaneously decrease in the recombination rate of electron-holes due to which intensity decreases and peaks are broader.

A decrease in PL intensity indicates (i) inhibition of recombination of charge carriers, (ii) induce geometrical distortions and (iii) created oxygen vacancy.

Dear Raj Kumar,

I agree with the suggestions/comments from Mr. Sanjeev and Dr. Ganeshraja. The loaded metal basically acts as electron sink and thereby results in the suppression of electron-hole recombination. In this case, less electron would come back to the valence band and would emit lesser energy in the form of light. Subsequently, the intensity will be low. 

Good luck!

Dear Kumar,,

In addition to other dear researchers, It is well known that optical absorption of photocatalysts significantly influences their activity. Photoluminescence (PL) signalsand their intensity are closely related to its photocatalytic activity. Further addition of metal content of the samples reduces the PL intensities, due to shorter distance of inter band metal ions, which result in an energy transfer between nearby ions. Therefore, a concentration quenching process will occur, due to a non-radiative decay process.  However, the inherent relationships are very complicated, and can properly be disclosed only on the basis of PL attributes, closely related to dopant species. For band–band PL signals, the lower the PL intensity, the higher the separation rate of photo-induced charges and, possibly, the higher the photocatalytic activity. For excitonic PL signals, the lower the PL intensity, the higher the separation rate of photo-induced charges and, possibly, the higher the photocatalytic activity. The stronger the PL signal, the higher the content of surface oxygen vacancies and defects and possibly the higher the photocatalytic activity. Therefore, it can be suggested that the photocatalytic activity of samples can be quickly evaluated by means of PL measurements under a certain condition.

J. Liqiang, Q. Yichun, W. Baiqi, L. Shudan, J. Baojiang, Y. Libin, F. Wei, F. Honggang, S. Jiazhong, 'Review of photoluminescence performance of nano-sized semiconductor materials and its relationships with photocatalytic activity' Sol. Energy Mater. Sol. Cells, 90 (2006), pp. 1773–1787.

Good luck

http://www.sciencedirect.com/science/article/pii/S0927024805003570