168
is employed in connection wires (approximately 200  mg per diode) (Gassmann
et al. 2016). Figure 9.6 presents a microphotograph of a LED showing the overlapping of elements detected by X-ray fluorescence.
Figure 9.7 shows the estimated concentration of rare earth elements in 50 LED
bulbs.
The materials and elements used in the production of LEDs are considered critical, especially rare earth elements like lutetium, cerium, and europium, or
technological metals like gallium and indium and precious metals such as gold and
silver (Gassmann et al. 2016).
According to Ayres and Pieró (2017), critical materials are geologically scarce,
affecting commercial availability. In addition, these materials are used for very specific
Table 9.4 Element used in
the production of LEDs of
different colours
Colour
Material semiconductor
Infrared
Gallium arsenide (GaAs)
Aluminium and gallium arsenide
(AlGaAs)
Red
Aluminium and gallium arsenide
(AlGaAs)
Gallium arsenide and phosphide (GaAsP)
Aluminium, gallium, and indium
phosphide (AlGaInP)
Orange
Gallium arsenide and phosphide (GaAsP)
Aluminium, gallium, and indium
phosphide (AlGaInP)
Yellow
Gallium arsenide and phosphide (GaAsP)
Aluminium, gallium, and indium
phosphide (AlGaInP)
Green
Indium and gallium nitride (InGaN)/
gallium nitride (GaN)
Gallium phosphide (GaP)
Aluminium, gallium, and indium
phosphide (AlGaInP)
Aluminium and gallium phosphide
(AlGaP)
Blue
Zinc selenide (ZnSe)
Indium and gallium nitride (InGaN)
Silicon carbide (SiC) as substrate
Violet
Indium and gallium nitride (InGaN)
Ultraviolet Diamond (C)
Aluminium nitride (AlN)
Aluminium and gallium nitride (AlGaN)
Aluminium, gallium, and indium nitride
(AlGaInN)
White
Blue chip or phosphor ultraviolet (UV)
Source: Adapted from Gois (2008)
E. C. A. dos Santos et al.