Herschel had already seen quinine water glow blue in sunlight. Stokes, in 1852, showed that the glow is always a longer wavelength than the light that pumped it, and borrowed the name from fluorite.
That shift is why a blue lamp can make a plate look green: the material eats the pump and re-emits something it can afford. On this bench the meter sees the re-emitted beam, not the leftover blue.