Acoustoluminescence and sonoluminescence

Acoustoluminescence (AL) may be defined as the visible (VIS) light observed from the acoustic vibration of single crystals or granular media, whereas sonoluminescence (SL) is usually defined as the light coated by the acoustic cavitation of bubbles in liquid H2O. The Planck theory of SL asserts that both SL and AL are a consequence of cavity-QED-induced spontaneous emission from confined spaces of optical dimensions that periodically grow and collapse under acoustic vibration. The confined spaces in AL an the voids in granular media, and those in SL are the bubbles in liquid H2O. The AL spectra in ZnS and ZnS : Mn powder are derived by assuming that the frequency of the spontaneous VIS emission is equal to the frequency of the standing electromagnetic (EM) waves in voids between adjacent grains as required by cavity QED. AL from dislocations within the powder grains induced by acoustic vibration is neglected. The void fraction and the random distribution of grain radii define the standing EM wave frequencies. Computed AL spectra are found to be featureless and broadband so as to be consistent with experiment. (C) 2000 Elsevier Science B.V. All rights reserved.