How are Fluorescent Colours Made?

Due to the consistency of the certain energy levels of a molecule, most of the fluorescence emitted light will be of the same wavelength each time. Different wavelengths correspond to different colours and so a set colour will be seen for a set molecule. Due to the vibrational relaxation and internal conversion first, this colour is also independent of the wavelength of light absorbed.

As can be seen in the electromagnetic spectrum (Figure 3), UV light is at lower wavelengths than visible light and so for DFPs, the light absorbed is the UV light within normal daylight and then the light emitted is in the higher wavelength of the visible range so that the human eye can see it.

Figure 4: An example of an application of fluorescent pigments in the cosmetic industry in nail varnish.

Types of Daylight Fluorescent Pigments

Conventional DFPs

Melamine formaldehyde encapsulated pigments are among the most common types of DFPs. These offer high fluorescence as well as excellent solvent resistance and heat and light stability. Our Aurora SRA range is used in a wide spectrum of applications from safety signage through to novelty applications is available in a range of different colours.

New hybrid polymer DFPs

Formaldehyde is now known to have carcinogenic effects so in some industries formulators are looking to new formaldehyde-free technologies. Historically, low solvent resistance was the main reason that formaldehyde-free DFPs were not widely used as where incorporation into solvents was required, the encapsulated pigments would dissolve creating a gel. Optimisation of these resins went through several iterations but these were at the compromise of solvent resistance, pigment luminosity or stability. A hybrid polymer, as found in the Aurora AQA range, has been found to not only match but in some cases improve upon the formaldehyde-containing versions for solvent resistance without compromising on other features (Figure 5).