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Blacklights work in a similar way. There are actually two different types of black light, but they work on the same principle:
- A black light tube is basically a fluorescent lamp with a different type of phosphor coating. This coating absorbs harmful short-wave UV-B and UV-C radiation, while emitting UV-A light (basically, the phosphor in a fluorescent lamp absorbs UV light and emits visible light). What would be the fluorescent tube itself blocks most of the visible light, so in the end only benign long-wavelength UV-A light gets through, along with some blue and violet visible light.
- The incandescent black light bulb is similar to a normal bulb used in any home, but with the particularity of having a filter that absorbs light from the heated filament, except for infrared and UVA light, although some visible light is also .
In both the tube and the bulb, the UV light emission reacts with the phosphor coating, which glows as long as UV light is irradiated on it.
Materials to produce phosphorescence
The phosphor used for the phosphorescent reaction to occur is made from a material enriched with other elements, such as zinc activated by copper and zinc sulfide. These materials are called hosts, because they are capable of hosting the electron or electrons that change energy level.
A series of activators are also added to them that prolong the emission time, and another series of elements that quench the glow, shortening the disintegration period that allows the phosphor to emit radiation.
Whether by adding some elements or others, the coating is made from phosphor powder that is produced at low temperature, and that requires a production process that is carried out in several steps. The material obtained must be crushed to obtain the desired grain size, since if this size is exceeded, a poor quality coating is produced, while excessively fine grain produces less light and degrades quickly.
The phosphor powder also requires a firing process, which must be controlled to prevent both the phosphor activators from oxidizing and contamination from other elements that may be present in the process. After milling, the phosphor can be washed to remove minor excess activating elements. Volatile elements must not be allowed to escape during processing. At present, the composition of the elements that are added to the phosphor powder have been changed to avoid toxic elements, such as beryllium, cadmium and thallium.
With the passage of time, phosphorus gradually loses its effectiveness by various mechanisms, such as the change in valence of the elements used as activators by the oxidation process. In this way, the crystal lattice degrades, and the atoms, mainly those that are part of the activators, diffuse through the material, so that the surface undergoes chemical reactions with the environment, with the consequent loss of efficiency or the accumulation of a layer that absorbs excitation or radiated energy, among other problems.
The degradation or loss of electroluminescence, regardless of the device, depends on the frequency of the driving current, the luminance level, and the temperature; Humidity also significantly impairs the life of the phosphor.
Some examples of objects and substances that glow in the dark
- Quinine flavored tonic.
- Some vitamin complexes and medicines that include vitamin B12 tend to glow yellow.
- Chlorophyll glows red.
- Chameleon bones glow an intense blue, visible through living skin.
- Scorpions glow blue or green.e
- Teeth usually glow bright white under this type of light.
- Antifreezes.
- Fluorescent minerals glow with different colors.
- Many precious stones, including rubies, glow in black light.
- Approximately a quarter of diamonds shine with different colors.
- Some bodily fluids, such as urine and blood.
- The bank notes.
References
Castellon, M., & TORO, J. (2018). ► Black light – What is it, what is it for and how to make it. Retrieved 17 April 2022, from https://www.efectoled.com/blog/es/luz-negra-sirve-fabricarla/
Phosphorous Light Emitting Process and Materials. (2022). Retrieved 24 April 2022, from https://hmong.es/wiki/Phosphor#:~:text=Un%20f%C3%B3sforo%20es%20una%20substancia,alg%C3%BAn%20tipo%20de%20energ%C3 %ADa%20radiant .
FPS, R. (2022). Healthy Skin Foundation – News The difference between UVA rays and UVB rays. Retrieved 18 April 2022, from https://fundacionpielsana.es/prevencion/la-diferencia-entre-rayos-uva-y-rayos-uvb
Helmenstine, A. (2015). List of Things That Glow Under Black Light. Retrieved 17 April 2022, from https://sciencenotes.org/list-of-things-that-glow-under-black-light/
How Stuff Works, Science, Innovation, & Innovations. (2002). How Black Lights Work. Retrieved 17 April 2022, from https://science.howstuffworks.com/innovation/everyday-innovations/black-light.htm
