[Pw_forum] About the optical absorption edge juded from the absorption coefficient spectrum graph.

[Hongsheng Zhao]

Dear all,

I'm a newbie on optical peroperties calculations and have some confusions on the optical absorption edge juded from the absorption coefficient spectrum graph.

For detail, I'm reading the following paper:

First Principles Calculations of Electronic Band Structure and Optical Properties of Cr-Doped ZnO

The corresponding doi is as follows:

http://pubs.acs.org/doi/abs/10.1021/jp811507r

On the 3rd page of this paper, the author said:

------------------
the optical absorption edge
of Cr-doped ZnO will shift to the high-energy region compared
with pure ZnO, which will be discussed carefully below.
------------------


Then on the 4th page, the author said:

------------------
On the other hand, the absorption edge
of the Cr-doped ZnO systems shifts slightly to higher energy
with increasing Cr doping concentration. 
------------------

Corresponding to all of the above informations, the author give the results by their group in Fig. 6 of that paper.   
  
I post here the Fig. 6 of that paper for your information. Could someone please give me some hints on the above analysis based on the Fig. 6, especially how determine the optical absorption edge from the absorption coefficient spectrum graph.

Thanks in advance.

-- 
Hongsheng Zhao <zhaohscas at yahoo.com.cn> 
School of Physics and Electrical Information Science, 
Ningxia University, Yinchuan 750021, China
GnuPG DSA: 0xD108493
2011-2-3
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