Principle of Optically Detected Magnetic Resonance

In the conventional ODMR techniques, one monitors the luminescence intensity to detect ESR signals in terms of changes in luminescence at resonance. These changes are a consequence of spin-dependent recombination processes. For trapped electron - hole pair recombination, illustrated in Fig. 1, the spin-dependent nature of the radiative recombination can be easily understood by considering that radiative recombination is allowed when spins of an electron and a hole are antiparallel and is forbidden, in principle, when they are parallel. 

For simplicity, we assume that the generation rate is the same for four Zeeman levels of an electron-hole pair, i.e., G[N— (n, + /I2 + + 4)]  

R of parallel spin states and each Zeeman level is unthermalized, the populations of the antiparallel spin states become smaller than those of the parallel spin states. Associated with ESR transitions of either electrons or holes, the population of the antiparallel spin states becomes large. As a result, the luminescence intensity 7 increases compared with before the occurrence of the ESR transition. The quantitative calculation of (A///)esr, the relative change in /at resonance, has been done by Kaplan et al. (1978), Dunstan and Davies (1979), Movaghar et al. (1980) and Morigald (1981). Here, we present the calculated results, using the rate equations (Morigaki, 1981) 

The factor of 2 7 W/ 1 -I- 2 7 f IF) in Eqs. (2) and (5) is known as the saturation factor in magnetic resonance. For the saturation factor equal to one (strong microwave power case), the magnitude of (A///)esr reaches 100% when R is greater than R.  

In this case, one can also expect a large magnitude of (A///)esr when the saturation factor is equal to one. 

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