I am keeping the lamp warm for atleast 30 min but still I m getting 110% transmission . I am using Shimadzu solidspec-3700 uv- vis-nir spectrophotometer. Please help to resolve this issue.
Dear Vikash,
Did you do the baseline measurement without any samples both in the reference beam line and sample beam line? That is the first step to do after warming up the spectrophotometer after setting the parameters of T, step size or band width and scanning wavelength range. The reference beam should be kept empty after baseline. The reason behind is a theory with light shining on a sample to calculate the light output intensity from the sample.
Therefore this step is crucial if your sample is absorbed in the wavelength region. Hope it helps.
Here is another time when someone was having the same problem. It was a problem with the collection of the reference baseline.
https://www.researchgate.net/post/Could_anyone_please_explain_why_am_I_getting_more_than_100_transmittance_for_ZnO_thin_film
I think the normalization of data after the measurement is a plausible solution.
Tyler Hurst the wavelength range is between 350-500 nm for T>100% .
Xuhua Wang ma'am do you mean to consider air as reference ? In that case it was not crossing 100% but when i am taking ITO coated glass then its crossing 100%.
@Vikash Vashisht
First thing to do the baseline, you must use the air for both sample beam and reference beam. Then you should check when you measure the air ( nothing in the sample beam). The transmission should be 100%+/-0.05% across the whole range for the setting when you did the baseline. From this step, you can adjustify whether your instrument is OK or not. If not, the lamps in your system may need to be replaced. The lamps have lifetime.
If the instrument passes the above step, then measure your sample.
Hope it is clear.
Very best
Xuhua Wang ma'am the baseline with air 100%+/-1% for most of the range. do we need to change the lamp ? Thank you in advance .
@Vikash Vashisht
You could check the operating hours for the lamps used on the instrument from the time counter. The instrument manual normally has such information for whereabout.
Sometimes the parameters setting could affect the baseline too. For example, some low-cost budget spectrophotometer requests the band width setting must be 5nm instead of 2nm for most of spectrophotometer. If you set the band width for 2nm, the baseline error bar could be higher and sometimes off the range. Again do check the specifications of your instrument.
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