Old-style fluorescent tubes had a phosphor coating on the inside of the glass, and a low-pressure mercury vapour gas inside the tube. When the mercury vapour was excited it glowed with its normal emission spectrum, which consists of a bright band in UV and bands in violet, green, and red. The UV band excited the phosphor to fluoresce and emit white light. When I looked at them with my pocket spectroscope I could see a continuous spectrum across the visible band, and bright peaks in red, green, and violet. The diameter of the tubes was tweaked to maximise efficiency.

The spectrum of modern fluorescent tubes is completely different. There are emission bands in red, orange, green, and violet, and a faint spread of blue. The continuous spectrum provided by the phosphor of the older style is absent. The red, green, and violet appear to be about the same wavelength as for a normal Hg spectrum, suggesting a mercury vapour-type excitation, but I don’t recognise the other parts of the spectrum. Mini-fluoros (the replacements for incandescent globes) have the same spectrum.

Does anyone know what gases are used in modern fluoro tubes, and/or how they work, and if so would they please offer an explanation here?

Since the 1990s, higher quality fluorescent lamps use either a higher CRI halophosphate coating, or a triphosphor mixture, based on europium and terbium ions, that have emission bands more evenly distributed over the spectrum of visible light. High CRI halophosphate and triphosphor tubes give a more natural color reproduction to the human eye. The CRI of such lamps is typically 82–100.

http://en.wikipedia.org/wiki/Fluorescent_lamp#Phosphors_and_the_spectrum_of_emitted_light

I buy the LEDs now , fluorescents are on their way out