What's UV-visible/fluorescent spectra?

Bill_A_Nussbaumer at ms.bd.com Bill_A_Nussbaumer at ms.bd.com
Tue Nov 9 09:54:17 EST 1999

Bill A Nussbaumer at BDX
11/09/99 09:46 AM

A UV-visible spectra is generated by passing a light source through your sample
at all UV and visible wavelengths and measuring the amount of light absorbed at
each wavelength (you may remember from lab that % transmittance and absorbance
can be calculated from one another).  This can be visualized as a graph
containing wavelengths along the X-axis (usually between 200 nm and 800 nm - 200
is well within the UV region of the spectrum while 800 is at the high end of the
visible spectrum - think ROY G BIV- and then UV or ultraviolet).  UV and visible
spectra are essentially the same thing, only the wavelength in question
distinguishes them from each other.  A fluorescence spectra is similar in idea
but a bit different.  In this type of spectra only compounds that exhibit
fluorescence can be measured.  The light at different wavelengths is passed
through the sample and this time, instead of measuring the amount of source
light to pass through the sample, one measures the amount of light emitted by
the sample itself due to excitation from the source light.  Fluorescence is
generally given in terms of the excitation and emission spectra.  The excitation
indicates at what wavelengths the compound is being excited and it directly
relates to the wavelength of light being emitted while the compound is excited
at each wavelength.  It makes sense that the UV-Visible and fluorescence spectra
would be similar.  Think of it this way - if you were measuring a fluorescent
compound, it would need to absorb the light in order to get excited and
fluoresce light at a new wavelength.  Therefore if the absorption spectra showed
the greatest amount of absorbance at 400 nm (i.e. the "peak" of the graph) then
it makes sense that the same compound is excited at that wavelength.

I hope that made sense,

Bill Nussbaumer

"They have similar UV-visible/fluorescent spectra with a peak absorption at
about 400 nm."

Could someone kindly tell me what UV-visible/fluorescent spectra is? How can
the three terms(UV, visible and fluorescent spectra) be used together to
depict the peak absorption?

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