Constructing a Model to Explain the IR Detector Card

KSU Physics Education Group

Introduction

In the previous activity you completed several experiments using infrared detection material. Each of the experiments was directed toward understanding how the material can absorb infrared light and then emit higher energy visible light. In this activity you will work with a computer program that uses energy bands to create a model of the IR detecting material. By changing variables in the program you will be able to see how the model explains each of the observations in the previous activity

Energy Bands in IR Detecting Material

A figure of the IR detector card will appear on the left part of the screen and an energy scale will appear of the right part of the screen.

Notice that the energy scale contains a black set of horizontal lines located at -5eV. These lines represent the valence band of the IR detection material.

Create an Excited State Band (conduction band). A set of gray horizontal lines representing the excited state band appears next to the energy scale.

Click on the ‘Create Impurity State Band’ button. A set of gray horizontal lines appears in the energy gap.

The material that makes up the IR detector card consists of many solid atoms, including some impurities. Interactions occur among solid atoms that are relatively close together. Electrons bound to these atoms have allowable energies that are in both excited and ground state bands. The impurities create additional allowable energies in the impurity state band.

The program begins with a simulated IR detection material that is similar to material that has been exposed to an intense IR source. So, it must be exposed to some visible light before it will function. The Input Spectrum represents the source of this visible light.