Direct Energy, 2018a

168 7.5 Relationship Between Devices
Scientists have come up with a wide variety of devices that convert
between electricity and light,and they have come up with a wide variety
of applications for these devices. Covering all such devices and all their
applications is beyond the scope of this text. However,this chapter has
shown some of the variety of devices. One way to classify devices which
convert between electricity and light is to group them into categories based
on whether they primarily involve absorption,spontaneous emission,or
stimulated emission. Figure 7.10 illustrates how to classify many of the
devices discussed in this chapter in this way. Ovals indicate absorption,
rounded rectangles indicate spontaneous emission,and rectangles indicate
stimulated emission. In the gure,thick borders indicate categories of devices
while thin borders indicate example types of devices. Dotted lines
indicate devices with gaseous active materials,dashed lines indicate semiconducting
active materials,mixed dotted and dashed lines indicate solid
state active materials,widely spaced dotted lines indicate conductive active
materials,and solid lines indicate mixed or other active materials.
This diagram is far from complete because many other categories of
devices exist,and these categories may be broken into further subcategories.
Furthermore,only a handful of example devices are shown relating to some
of the specic devices discussed above. This diagram includes absorption
based devices discussed in Chapter 6. It also includes antennas discussed in
Chapter 4. Light is a form of electromagnetic radiation with frequencies in
the visible range. Light can be absorbed by a solar cell and spontaneously
emitted by an LED,for example. Similarly,electromagnetic waves at longer
wavelengths can be absorbed or spontaneously emitted by antennas which
are devices with conductive active materials.
A dierent way of classifying devices which convert between electricity
and light is to classify them based on the type of active material. All of
these devices involve the interaction of light and atoms. The atoms involved
may be part of a gas,may be dopants inside an insulating solid,may be
part of a bulk semiconductor material,or may be part of a conductive
solid. This way of classifying devices is illustrated in the Fig. 7.11. Dotted
lines indicate devices with gaseous active materials,dashed lines indicate
semiconducting active materials,mixed dotted and dashed lines indicate
solid state active materials,widely spaced dotted lines indicate conductive
active materials,and solid lines indicate mixed or other active materials.
As in the previous gure,ovals indicate absorption,rounded rectangles
indicate spontaneous emission,and rectangles indicate stimulated emission.
Antennas are shown twice in the conductor based devices category because
receiving antennas involve absorption while transmitting antennas involve
spontaneous emission. Also as in the previous gure,thick borders indicate