Substances that emit light after they have been exposed to a light source are called long persistence phosphors. These materials are composed of a phosphor and a activator. The activator adds imperfections to the crystal lattice and is also referred to as a dopant. Without these imperfections, the crystal would not be able to send out light. The activator or dopant is also responsible for the color of the light being emitted. In the past, zinc sulfide with copper as activator was the most used substance (the copper gives the light the well known green color).
Next generation phosphors
However since recently, there is a new phosphor on the market. It is called strontium aluminate and is doped with europium and dysprosium. The light it emits is many times brighter and the glow persistence is also much longer. By changing the production process a little, the color can vary from green to blue. Green gives the most bright light but blue has the longest glow duration. Other colors are also possible but it has a negative effect on the brightness. Below, we have made an overview of the most used materials with some information about their properties and health risks.
List of popular phosphors
Zinc sulfide (green, red and orange)
This substance is not known to be carcinogenic nor to be toxic. However the toxic substance hydrogen sulfide may be released when it is ingested.
Strontium aluminate (green, aqua and blue)
This compound is biological inert and is considered to be safe. Water will dissolve it. So when you mix it with water, you have to apply it quickly.
Calcium sulfide (blue)
Considering this material is also used as an addition in food products, we should be able to say that it is safe.
Strontium sulfide (red)
This compound is not carcinogenic. It may be irritative to the skin. When ingested, the very toxic hydrogen sulfide is released.
The following substances are, along with strontium aluminate, next generation phosphors.
Yttrium oxide sulfide (red)
This material has not had a lot of research. However to this date, it is considered to be nontoxic. Nevertheless we still advise you to handle it with care.
Is very resistant against water and most acids. Therefore you can use it in almost every medium. As far as we know there is no knowledge about it’s possible toxicity. However it would be wise to use it carefully.
List of dopants
Since the amount of dopant in the crystal is very low, we do not discuss them in this article. The most popular dopants are: copper, europium, dysprosium, titanium, magnesium, bismuth, silver, manganese but there are many others.