Photoacoustic spectra from Co doped ZnO with different grain or cluster sizes

Photoacoustic (PA) spectra for Zn1-xCoxO mixed-crystal powders with various Co concentrations and sintering temperatures were measured. The PA spectra showed three peaks of Co2+ absorption between 560 nm and 660 nm. On the other hand, the PA spectra between 800 nm and 1000 nm were almost flat, and these are expected to he dominated by light scattering effects. The PA spectra were normalized by using the Co2+ absorption peaks in order to compare the sample size and the PA signals intensity, and the sintering temperature dependence of the PA spectra is discussed. The PA signal intensity decreased with the increase of the sintering temperature. The decrease of the PA spectra seems to be caused by small light scattering effects for the large clusters under higher temperature sintering, where the grains and clusters size increase. We could evaluate the grain growth in the sintering processes by PA spectroscopy in a noncontact mode.