Is it possible in UV-DRS, reflectance is more than 100% of metal oxide ?
Dear Aniruddha Mondal
No you cant refledtance is more than 100%
All the Best
Reflectance is defined as the ratio of reflected (Ir) and incident energy (Io): R=Ir/Io and it is not possible to be more than 100%. Check again your measurements and the way that you take baseline. Do you make all necessary corrections?
ya , i checked in two different instrument , i.e. hitachi .... but i got 110% reflectance , how it can be solved ...... ??
Dear Aniruddha Mondal
It is not possible Because
Reflectance+Transmittance+ absorbance =1
Reflectance =1-(Transmittance+ absorbance)
I think u are getting more than 100% reflectance because u have not set the baseline. So first you should set the base line, after setting the base line you will not observe the more than 100 % reflectance. for set the baseline in Perkin Elmer used BaSO4 powder .and in UV-DRS used the teflon coated BaSO4.
all the best
Hi,
I think repeat once again your measurements especially check the baseline.
As you don't describe the equipment you use, I treat the situation in general. Let us assume that you properly measure the baseline signal and your calibration standard is not contaminated or severely damaged. I would suggest the following thinkable but not very probable reason how you obtain reflectance over unity. Your calibration standard is supposed to be a Lambertian reflector, fully diffuse, no specular component. If your sample is, on the opposite, quite mirror-like reflecting and you are using not the integrating sphere but praying mantis setup or alike (that is, you measure only a part of solid angle, not the full sphere) then your signal could indeed peak above the physically meaningful limit. Solution - check the baseline and calibration procedures with the original manuals of your equipment step-by-step, make sure you haven't omitted anything, particularly the way you reject or take into account specular reflections.
One more thing to care about could be luminescence. If your material contains transition metal or rare earth ions, you potentially could excite light generation in your sample, especially when you are scanning the short wavelength range. Your sample would not only reflect light from the source but also transform a part of the absorbed radiation in emission at longer wavelengths. Clearly, it should not increase the reflectance over unity per se, luminescence is a lossy process. But if your detector is more sensitive for longer wavelengths, it could noticeably affect the results you get towards the short wavelength end of the spectra.
Definitely not possible, that means photons get created out of nowhere!
Because the value above 100% in reflectance is ascribable to luminescence effects. The only way you have to confirm experimentally this effect is to put an optical filter able to block the luminescence just before the photomultiplier tube.
Hi,
I am also getting more than 100% reflectance, where I have chosen baseline 0-100%. Can anyone give me suggestions for the same?
You will need to know what substrate your sample is coated on. If your substrate is diffused, then use a diffused calibration standard (usually porous PTFE). If your substrate is polished mirror finish, ie silicon wafer, use specular calibration standard (usually MgF coating). Otherwise use a clean substrate of your sample and use it as the blank.
In my case, my sample is coated on silicon wafer, however due to very weak reflectance, I used diffused calibration standard. This is where the reflectance signal will exceed by 200-300%. This sample signal can be deducted with the blank silicon signal, and gave much more reproducible results than using silicon wafer as the calibration standard instead.
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