This document discusses optical properties of materials used in opto-electronic devices. It introduces key optical phenomena such as reflection, refraction, absorption and scattering that occur when light interacts with materials. The optical properties of non-metals, metals and semiconductors are determined by their electronic structure and response to electromagnetic radiation. Important devices discussed include photoconductive cells that convert light into electrical signals based on the photoelectric effect.

1. Materials for Opto – Electronic Devices:
Introduction,
Optical phenomena,
Reflection, Refraction, Transmittivity, Scattering,
Optical absorption,
Optical properties of non-metals, Optical properties of metals,
Optical properties of semiconductors,
Optical properties of insulators.
Luminescence, Opto – Electronic devices,
Photoconductivity,
Photoconductive cell.

3. • By optical property we mean the response of a material against exposure to
electromagnetic radiations, particularly to visible light.
• When the light falls on a material, several processes such as reflection,
refraction, absorption, scattering etc. take place due to interaction between
the light and material.
• The e.m.f. of the light radiation interacts with the changes contained in a
material to exhibit its different optical properties.
• The nature and distribution of charges in a material play an important role in
determining the optical properties.

4. Important Terminologies Related to Optical Materials

7. photoelectric effect

8. Optical Phenomena
Interaction of Light with Solids : When a beam of electromagnetic (EM)
radiation falls on a solid medium, the light interacts in different ways
as given below.
1. Some light is reflected from the surface of the medium
2. Some light is absorbed within the medium, and
3. Some light is transmitted through the medium.

11. Reflection

12. Refraction
• Not all the radiation that is incident on a material gets scattered out of the
material.
• The newly generated radiation due to the oscillating dipoles, interferes with
the incident radiation and propagates into the material with a phase
retardation.
• The speed of the wave that propagates inside the material is lower than that
of the incident radiation.
Refractive Index

15. Relation between Refractive Index and Dielectric Constant
The value of εre depends on the number of electrons encountered
per unit length and their polarizability.
Thus a denser material has larger n.
For example, the quartz of specific gravity = 2.65
has the value of n = 1.544 as compared to
silica of specific gravity = 2.2 which
has the value of n = 1.458, although both are silica.