Considering a typical emission scan experiment, why does the intensity increase successively after each measure?
PS1: All measurement performed in a solution with constant concentration
PS2: Also considering the same value of slit and integration
Hi, M. Farooq
The fluorophore is a ruthenium complex.
''(2) Another possibility is that the xenon lamp is taking a long time to warm up because fluorescence is directly proportional to the source intensity.''
Before starting the experiment, I allow the heating lamp for about 20 min...
All modern scaning spectrofluorometers have reference detector and registered ratio I_sample / I_reference for compensation of lamp flicker. But if you use CCD-spectrometer for registration of luminescence with Xe-lamp as excitation source then situation (2) described by M. Farooq Wahab may be realised.
In any case, make experiment with quinine sulfate or any standard.
In some cases, when compound is unstable, the absorption or fluorescence may be changed during the measuring spectra. You did not specify the structure of the Ru-complex, so it is difficult to predict its photostability. So I make this assumption.
Hi M.Farooq,
I'll wait more time to warm up the lamp ... you're right, my complex is very stable, I suppose. It's like a Ru (bpy) 3 ...
The ratio between the first and second measurement is about 1.06 and the ratio between the first and the last one is about 1.2. Thanks for the suggestion, i'll use quinine.
Hi Ruslan,
As I described to M.Farooq my compound is stable and I don't believe it's suffering photolysis, my apologies, I did a poor description of my problem. Also I don't see any shift of wavelength.
For my experiments, I use a quanta master 40 (PTI) equipped with Xe-lamp. I suppose that the detector is the CCD type, I'll make sure. Thanks for the suggestions.
Is it possible that the concentration of your sample is increasing over time due to evaporation of the solvent?
Hi Adam,
Not likely, I'm using an aqueous solution at 20oC. I conducted an experiment with a standard (Ru(bpy)3) and do not see anything atypical. Maybe is something related to my compound.
may be some photochemical reactions occues and the concentration of dye changes or the the intensity of excitation light changes due to electrical current
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