Fluorescence intensity is increasing as the time passes. Emission wavelength remains the same.
Intensity is changing upon variation in concentration also. But, emission wavelength is still the same.
Intensity is directly related to concentration. (In fluorescence we do not talk much of concentration instead we use absorbance.) If you want a quantitative analysis check the quantum yield with concentration. Quantum yield is independent of concentration.
If the intensity changes with time maybe it is a case of surface passivation, solubility/aggregation/dispersion issue. Yes aggregation may affect the intensity.
For highly absorbing quantum dots there will be a saturation of the fluorescence intensity with concentration as in the moment the optical path shortenes because light can not pass the cuvette any more you have a nonlinear change of the fluorescence and probable it does not even rise or can even drop with rising concentration. There is a nice book on the topic, however it is not available at the moment and in German only:
https://www.amazon.de/Fluoreszenz-Organischer-Verbindungen-Theodor-F%C3%B6rster/dp/3525423128/ref=sr_1_1?ie=UTF8&qid=1536611094&sr=8-1&keywords=f%C3%B6rster+theodor+fluoreszenz+organischer
If anyone can sell this book I would be interested !
Förster is the best, however there is also the Lokowicz mentioning few of these phenomena:
https://www.springer.com/de/book/9780387312781
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