[Telamond]

From what I've gathered from my text book and from my notes both of them enhances the intensity of the analyte.

I was wondering is one of the detector better than the other and when you use them?

Also, why is the detector in a 90^o angle from the light source in a fluorescensspectrometer?

And what's the difference in an excitationspectrum and an emissionspectrum in a spectrofluorimeter?

Sorry for the bad english... not a native speaker. ^^

Thank you for any assistance/time.

[Arkcon]

From what I've gathered from my text book and from my notes both of them enhances the intensity of the analyte.

The diode array and photomultiplier tube are two types of detector hardware, they don't amplify a signal, without one of them, there is no signal.

I was wondering is one of the detector better than the other and when you use them?

Depends really, cost is probably the biggest issue.  Photomultiplier tube technology is ancient, therefore well known, and therefore inexpensive.  Have you read about a difference in how the photomultiplier tube and diode array work?  You should see an important piece missing in the post-sample side optics of a diode array, when compared to a photomultiplier tube instrument.

Also, why is the detector in a 90^o angle from the light source in a fluorescensspectrometer?

Can you see how an absorbance spectrophotometer differs in function from a fluorescence spectrophotometer, and why the 90 angle is needed?

And what's the difference in an excitationspectrum and an emissionspectrum in a spectrofluorimeter?

Those are two separate types of readings from a fluorescent sample.  Read more, and it will be clear.

Sorry for the bad english... not a native speaker. ^^

Thank you for any assistance/time.

Not a problem, but do use the spell-checker, it's easier on everyone, and helps you learn as well.

[ARGOS++]

Dear Telamond;

That’s quite a couple of Questions,  - Huh!
It needs a little time to answer.  Please give a little time!

In the mean time you may inform you already on:
For your 90° Question on:   " Fluorescence Spectroscopy”

For a lot of Advantage for DAD’s (= PDA’s) visit:  "Spectroscopy FAQ”

Good Luck!
                    ARGOS⁺⁺

[Telamond]

Thank you both for your help.

From what I've gathered now the answers to my questions should be something like this, please correct me if the answers are wrong. Also, realised that most of my questions were unclear... I apologize for that.

Also, why is the detector in a 90^o angle from the light source in a fluorescensspectrometer?

90^o angle is because you want to measure the emission and not the excitation energy.

And what's the difference in an excitationspectrum and an emissionspectrum in a spectrofluorimeter?

The emissionspectrum gives their peak at a lower wavelength due to Stoke's shift.

I was wondering is one of the detector better than the other and when you use them?

I'm still a bit uncertain about this question... I tried reading the links that ARGOS⁺⁺ posted but couldn't find anything of interest, unless I missed it.
Neither did I find anything missing after the sample-cell. But it could also be because neither my text book nor my hand-outs has a good overview of the part. Other than cathode, anode and several dynodes.

[Arkcon]

The emissionspectrum gives their peak at a lower wavelength due to Stoke's shift.

The emission wavelength is usually longer, that is father into the red end in the case of the visible spectrum, lower energy, wavelengths, than the excitation wavelength.  This wavelength "distance" as it were, is called the Stoke's shift.

[redskytonight820]

From what I remember, the difference between an excitation spectrum and an emission spectrum, is that the emission spectrum is obtained when the emission intensity is recorded at a variable wavelength, While an excitation spectrum is constructed when the luminescence intensity is measured at a fixed wavelength, while the excitation wavelength is varied.

It should also be noted, and I have no idea if this would be helpful to you but, the excitation spectrum is pretty much the same as the absorption spectrum... So I guess, if you wanted to gather a different set of data points, or, if you were looking to gather data from another viewpoint, then you'd best take an emission spectrum since it will give you another take on your experiment.

Hope this helps!

[ARGOS++]

Dear Telamond;

Great!,  -  You did quite a couple, even if not all very well.
(Not only what Arkcon already corrected.)

Let’s “walk” through your last Posting (# 3):

Using an angle of 0° would result in a Spectrum mixed from “Excitation” (in real an Absorption) with the resulting “Emission Spectrum”. And how would you now like to separate both, to get the wanted  “Emission Spectrum”?   But you can be lucky, because the molecules will emission the resulting Photons in all directions. So you are able to measure the “pure” "Emission Spectrum” without ‘any’ other influence of the “Excitation Spectrum”, if you measure by 90°.

And what's the difference in an excitationspectrum and an emissionspectrum in a spectrofluorimeter?

The emissionspectrum gives their peak at a lower wavelength due to Stoke's shift.

Arkcon has given you already a correction to your answer, but it is not complete.
Your answer tells me, that you not really caught what “Fluorescence” is, and that you can measure it in a “Fluorescence Spectrometer” or a “Fluorometer”, because both term mean the same.
With the “Excitation Light” you excite a Electron to a higher (mostly the next) “Energy level” and finally the Electron returns to the “Groundstate” and in case of “Fluorescence” it emits a Photon, and if its energy falls into the visible range you can see it with your eye.
But that means you have at least to spend the electron enough energy to reach its excited state, and that means “Excitation Wavelength” must be at least as short, or even shorter as the wavelength you can measure as the “Emission Wavelength”, because as shorter the Wavelength as higher the Energy (absorbed or emitted) will be.

Yes!,  - Dear Redskytonight820; - that’s also partially very true, that very seldom (-if-) both wavelength are varied at the same time. But quite often Excitation is done by using a certain rang of Wavelengths below the lowest “Emission Wavelength” you would like to record, because a higher “yield” of Photons. The second part of your answer must be ‘headline-ed’: “Only looks similar”, but that’s an additional theme.

But that’s not enough! As your “Groundstate”, as also your “Excited State”, are overlaid by the corresponding “Vibrational States” (a lot for each), you excite your electron into a lot of different “Vibrational States” of  the “Excited State”, but the “Fluorescence” starts ‘all times’ from the lowest “Vibrational State”. So the electron has first to lose some of its “Excited Energy” to reach first the lowest “Vibrational State”; and that results in a so called “Red Shift” of the “Emission Spectrum”, or in this case called “Stokes Shift” (Direction to Read means less Energy).
(Remember: The “Emission Spectrum” is not the mirror of the “Excitation Spectrum”, as most people think/believe!)
Maybe for some visualisation you may visit:  "JABLONSKI Diagram”?

For the advantages of DAD’s /PAD’s over Photomultipliers you would have been able to find, under the Question “How does UV/Vis Diode Array Spectrometer (PADs/DADs) work?”:

…………
E)  CCD's Charge Coupled Device Detectors have, by their construction/electronics, only a few, and rarely required Advantages over PDA's/DAD's, but several Disadvantages!
F)  Some other important "Adjectives":
      • Single Beam  (mostly).                                   • No closed Sample Compartment required!
      • Real Spectrum instead of Single Wavelength.    • Predestinated for reliable Spectroscopy.
      • Really fix Wavelength scale.                            • Only quasi equidistant Wavelength scale.
      • Quasi fix Wavelength resolution.                      • Time stable Wavelength resolution!
      • Exorbitant stable! (>15 Years/>30 Instr.!)         • Predestinated for reliable Chemometrics.
      • Predestinated for stable/secure Production.       • Predestinated for validated Quality Control.
      • etc.   
G)  etc.   

Additional can be told, that you can, with a DAD, take a Spectrum of your Peaks for Identification. But not only, you can take a Spectrum at the start of your Peak, one at the maximum of your Peak, and one near the end of the peak. But for what?  You can give the evidence that your analysed Peak is as good as you ever know, build from only “One/Pure Compound”.
I think:    Not 'nothing', because it costs you ‘nothing’, but gives you a lot.
The Spectra are also very important for Validation/Identification of Method and Compound.
You can also ‘misuse’ DADs as a “Multi-Single-Wavelength-Detector”, and so on, and so on.

A Disadvantage may be the shorter dynamic range in Absorbance (0.0 till ~1.8 AUs), but depends more on your calibration of your method.
But what a lot of people believe, that the “Sensitivity” must to be lower is not true, and mostly caused by their wrong handling of the DAD.

Huuuch…..!    I told you it will be a lot to write!

I hope it will be at least of some help to you.


Good Luck!
                    ARGOS⁺⁺