《固体化学》课程教学课件（英文讲稿）Chapter 8 the optical, electrical and magnetic properties of solids

Optical properties of solidsRubylaserLaserGallium Arsenide laserSolid state optical devicesLight-emitting DiodeTheinteraction of light with atomsA atom absorb a photon of light with correctwavelength, it undergoes a transition to a higher energylevel

Optical properties of solids Light-emitting Diode Solid state optical devices Laser Ruby laser Gallium Arsenide laser The interaction of light with atoms A atom absorb a photon of light with correct wavelength, it undergoes a transition to a higher energy level

The interaction oflight with atomsSelection rules:Electron cannot change its spinOrbital angular momentum of the electron must changeby oneunitIn terms of quantum number △S=0, △l=± 1For a sodium atom, for example, the 3s electron canabsorb one photon and go to 3p level. The 3s electron willnot, however, go to the 3d or 4s level

The interaction of light with atoms Selection rules: ● Electron cannot change its spin ● Orbital angular momentum of the electron must change by one unit In terms of quantum number △S=0, △l=±1 For a sodium atom, for example, the 3s electron can absorb one photon and go to 3p level. The 3s electron will not, however, go to the 3d or 4s level

The interaction of light with atomsForbiddenAllowed4p4p--t一七3d3dCa千t+Ht4s4s2p2p+-十2s2sHe4Ht千Ht1s1s3s3s+0一+4#1444千2p2p

The interaction of light with atoms

Theinteraction of light with atomsIt can do this in several ways:(1) Simply emit a photon of the correct wavelength atrandom some time after it has been exited;--Spontaneousemission(2) A second photon come along and induce the electron toemit:----Induced or stimulated emission(3) The atom collide with another atom, losing energy inthe process, or give energy to its surroundings in the formof vibrational energy.-----non-radiative transition

The interaction of light with atoms It can do this in several ways: (1) Simply emit a photon of the correct wavelength at random some time after it has been exited;-Spontaneous emission (2) A second photon come along and induce the electron to emit;-Induced or stimulated emission (3) The atom collide with another atom, losing energy in the process, or give energy to its surroundings in the form of vibrational energy.-non-radiative transition

Stimulated emissionemissi0nabsorptionhv>SIE>S>S1

E hn absorption emission Stimulated emission

Population inversionMirrorMirrorE

Ei Ef Mirror Mirror Population inversion

Spontaneous emissionMirrorMirrortE

Ei Ef Mirror Mirror Spontaneous emission

Stimulated emissionMirrorMirrorEttSE

Ei Ef Mirror Mirror Stimulated emission

Feed-back by the cavityMirrorMirrorEM:E

Ei Ef Mirror Mirror Feed-back by the cavity

Stimulated emissionMirrorMirrorE,W1IM:MMM1E

Ei Ef Mirror Mirror Stimulated emission