Glow in the Dark (Phosphorescent) Technologies
Alkaline Earth Metal Aluminate
Stontium Aluminates are good relevant example of Alkaline Earth Metal Aluminate.
Technology originating in 1992 provides an extreme variety of brightness's and economy levels in glow pigment. At the high end, offers the brightest and longest lasting phosphorescent pigments.
Depending on the individual product, "earth metals" can include Strontium, Magnesium, Calcium, and Barium. Silicon and Titanium may also be present. It is typically doped with Europium.
Glow Colors range in the spectrum from Green-Yellow to Purple-Blue.
Raw pigment is whitish in color, and translucent in medium.
Acid decomposes this pigment.
Water will slowly dissolve it. Therefore water-based mediums must be mixed, applied, and encouraged to dry quickly.
Alkaline Earth Aluminate w/Fluorescent Pigment
Products are created by taking Alkaline Earth Metal Aluminate pigments and adding an opaque fluorescent pigment to provide visibility in a lit room. As a side effect, the fluorescent pigments also tint the glow which can produce glow colors such as Orange.
Coated Alkaline Earth Aluminate
This technology is new for 2004. Products are created by coating Alkaline Earth Metal Aluminate pigments with a sealer to protect them from water. Because they are no longer water soluble, they can be used in water-based mediums.
Alkaline Earth Silicate
Another fairly new pigment technology that produces a very pure sky blue glow color not available from alkaline earth aluminates.
Pigments are not water soluble and are stable in most acids. Thus the medium choices are almost endless.
Zinc Sulfide (green formula)
Originated in the 1970's, this was the first phosphorescent pigment. It is also the pigment in 99% of all glow in the dark items currently available. It is not very bright and it only glows for a short period.
The reason it is used so much in manufacturing is that it is relatively cheap. It is also FDA approved for limited use cosmetics.
Raw pigment has a strong sulfuric odor, but it is usually masked when mixed into the medium.
Zinc pigments are slightly soluble in water. The solubility level is so small that they can be stored as a water-based paint for years.
Zinc Sulfide (red and orange formula)
In 2000, they manipulated Zinc Sulfide to produce glow colors in the color spectrum from red to orange. Colors are deep and pure. Brightness has been improved.
Raw pigment has a strong sulfuric odor, but it is usually masked when mixed into the medium.
Zinc pigments are slightly soluble in water. The solubility level is so small that they can be stored as a water-based paint for years.
Strontium
Strontium is a chemical element in the periodic table that has the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically.
Strontium aluminate is vastly superior phosphor than its predecessor, copper-activated zinc sulfide; it is about 10 times brighter, 10 times longer glowing, and 10 times more expensive than ZnS:Cu. It is frequently used in glow in the dark toys, where it displaces the cheaper but less efficient ZnS:Cu. However, the material has high hardness, causing abrasion to the machinery handling it; coating the particles with a suitable lubricant is usually used when strontium aluminate is added to plastics.
Strontium aluminate phosphors produce green and aqua hues, where green gives the highest brightness and aqua the longest glow time. The excitation wavelengths for strontium aluminate range from 200 to 450 nm. The wavelength for its green formulation is 520nm, its blue-green version emits at 505nm, and the blue one emits at 490nm. Colors with longer wavelengths can be obtained from the strontium aluminate as well, though for the price of some loss of brightness.
Europium
Europium is a chemical element in the periodic table that has the symbol Eu and atomic number 63. It was named after the continent Europe.
Strontium aluminate activated by europium, SrAlO3:Eu, is a newer material with higher brightness and significantly longer glow persistence.