Baseline Correction: What is the concept of a baseline shift and baseline correction?
Baselines are visually simple, most of the time, but can be a pain to filter.
With your graph, for instance, what should happen between 380 and 400 is not clear.

With fluorescence, it is not sure you can get a fine model of the baseline. So effectively, in many analytical instruments, there are more or less automatic baseline fits: constant, linear, parabolic. 

Without hard models, it is common to use soft ones, but we need to know what you want to quantify in your data. If it looks like other analytical chemistry data, where you want to measure peaks above a baseline, you may try the technique given in Chromatography Baseline Placement, combining low-pass filtering and peak preservation.

Is there any chance you could share the dataset?