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Phosphors are substances that exhibit luminescence and are often transition metal compounds or rare earth compounds of various types (not to be mistaken for the chemical element phosphorus P). They are used in CRTs, fluorescent lamps (FL), compact fluorescent lamps (CFL), cold cathode fluorescent lamps, light emitting diodes (LED) and other devices.
The phosphor layer in a CRT monitor is very thin (few nanometres), thus only small amounts are used per monitor (ca. 5-7 g). It is a white powder that is coated on the inner surface of the panel glass. When electrons strike the phosphor, it emits light. Depending on its composition, the light appears in different colours. To generate the colours red, green and blue, the panel glass is coated with three different phosphors, that contain e.g. zinc sulphide, cadmium sulphide, compounds of yttrium and europium. The powder consists of a large variety of elements, among them also hazardous ones (see Table). In black/white CRTs, the phosphor layer contains significant amounts of toxic cadmium (Cd).
The phosphor layer in a TV or computer CRT can be easily located on the inner surface of the panel glass.
Composition / main substances of content
The phosphor layer contains the following hazardous substances: Yttrium (Y), Cadmium (Cd), Barium (Ba) and Lead (Pb).
Storage and transport
The phosphor layer has to be stored in a closed recipient (cover!) which prevents its release.
Caution during dismantling
The generation of phosphor dust should be avoided during dismantling. It is recommended to wear a dust mask. To protect the worker, the air around the workplace should be aspirated by a fume hood.
Phosphors contain both valuable and hazardous elements. There are two alternatives for their treatment:
- Storage: If possible, the elements contained in the phophors should be recovered. Due to the lack of adequate technologies, this is not viable for many elements contained in phosphors at present. But given the content of valuable elements and the rising prices for rare metals, it might be not only environmentally, but also economically advantageous to store the phosphors until appropriate technologies are available.
- Disposal in a HW landfill: It should be ensured that the phosphors are disposed in a safe landfill which prevents the release of the hazardous substances (e.g. leachate) into the environment. By landfilling phosphors, a potential recovery of the contained valuable elements is impeded.
Source of information
Dismantling Guide for IT Equipment, which was elaborated within the SRI project and financially supported by SECO and UNIDO, June 2015