Self absorption. 
There was a similar question a few weeks ago. 


Sent from my iPhone

> On Jun 22, 2017, at 11:11 AM, Weizi Yuan <> 
> wrote:
> Dear all,
> I have measured some spectra of a CeO2 film(~200nm) grown on Yittria 
> stablized Zirconia(YSZ) substrate under 2 conditions.
> (i) room temperature, ambient atmosphere
> (ii) room temperature, vacuum (pO2~1E-6 atm) inside a graphite dome of  the 
> DHS 1100 anton paar,
> The spectra are collected in fluorescence mode. The incident angle is 3 o  
> and the fluorescence collection angle is 90 o.
> My questions are: 
> (i) From the theory behind the FLUO program developed Dr. Daniel Haskel, CeO2 
> spectra collected with a 3 o incident angle would have a strong self 
> absorption effect and need
>  correction , however, the signal is not attenuated compared with the CeO2 
> powder taken in a transmission mode, shown in attached plot.
> I've gone through many literature and people sometimes tell that whether  
> they have a successful self absorption correction by comparing the spectrum 
> with a spectrum taken under a transmission mode.
> So I'm wondering if I can say that I don't need a self absorption correction 
> in this case? 
> (ii) 
> The Ce4+ peak in the spectrum collected under condition (ii) has a much lower 
> intensity. I think it is due to the reduction of Ce 4+ under vacuum, however, 
> the Ce3+ peak does not show an increased signal here. Which makes ma doubt 
> whether this is simply reduction of Ce or might be from over absorption? 
> Thanks for any response. 
> <spectra.jpg> 
> -- 
> Regards,
> Weizi Yuan,
> Graduate Student,
> Northwestern University,
> Ph:(+1)312-560-9619
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