1650°C for a few hours in an oxygen partial pressure of 10−3 atm, cooled, and the spectrum is takenagain. If the after spectrum is subtracted from theas-received spectrum, the spectrum of the trappedhole center results. This works well on syntheticcorundum samples, and on natural corundumsamples if great care is taken to position the sample as described above. Heating for a few hours at1650°C has little impact on a sample that has beenheated for a few tens to hundreds of hours at temperatures of 1800°C or above. For the workdescribed here, the second or third method wasused on all samples, as the first method proved tobe too inaccurate.Chemistry. Secondary ion mass spectrometry withelement-in-sapphire standards (again, see SIMSBox A) was used at Evans East to determine Be andother trace-element concentrations in some of thenatural Be-diffused wafer samples used for absorption spectroscopy, and in some of the syntheticsamples before and/or after Be-diffusion treatment.