MadSci Network: Physics

Re: can a photoelectric cell be made to absorb any frequency of light?

Date: Mon Mar 19 11:56:13 2001
Posted By: Karl Kolbus, Staff, Data processing, Mequon Consulting Corp.
Area of science: Physics
ID: 981350399.Ph

Hello James,

For all practical purposes, a photocell does respond to all wavelengths of 
light; light being but a small part of the electromagnectic spectrum. What 
makes a photocell create electron flow is its' constituent parts - the 
materials that have electroluminescent properties. If we look at a simple 
Light Emitting Diode (LED), we can see that the wavelength of light 
created is a function of the materials it is "doped" with. Some of the 
more common materials are Ga, Ar, Se, In, Al, Ge, N, and P. You can look 
them up in your periodic table of the elements for their full names. By 
analyzing the output curves of a particular device, you will see that it 
is a bell-shaped curve, with the maximum light output at the wavelength 
determined by its' chemical composition. Other frequencies of light are 
produced, but drop off rapidly only a few nanometers on either side of the 
peak frequency. Here is a link to a cyan (blue) led from Agilent 
Technologies; a division of Hewlitt Packard, which illustrates this.
Note: You will need Acrobat Reader to view the datasheet.

In theory, it would be possible to create a photocell that is responsive 
to all wavelengths of light, but the practicality of it is quite another 
matter. To achieve an ideal photocell, i.e. the same output (mW/cm2) 
regardless of the wavelength of light incident upon it, would be a 
daunting task; to say the least. What's more, the sun, being the most 
abundant light source, is made up of all wavelengths of light - but in   
varying proportions. As the sun changes position in the sky, the 
proportions of "white" light to that of infrared and ultraviolet change 
dramatically due primarily to atmospheric absorption of certain 
wavelengths. Even the human eye is not perfect. We cannot "see" infrared 
or ultraviolet at all (some insects can see ultraviolet), and our eye's 
sensitivity to all wavelengths of visible light is not equal. For example, 
our eyes are more sensitive to green light than to red.

The following link is to an interesting article on the Photon Belt.

Your not-so-mad scientist,

Karl Kolbus

Current Queue | Current Queue for Physics | Physics archives

Try the links in the MadSci Library for more information on Physics.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2001. All rights reserved.