Sonoluminescence (SL) observed in the collapse of bubbles in liquid H2O may be explained by the Planck theory of SL, which finds basis in quantum mechanics and relies on the bubble walls to be blackbody surfaces as originally envisioned by Planck. By this theory, the source of SL is the electromagnetic (EM) radiation field of the bubble wall described by the absorption (and emission) spectra of liquid H2O from ultraviolet (UV) at ~254 nm to soft X rays. During bubble collapse, the resonant frequency of the bubble cavity always increases. If the resonant frequency coincides with the EM radiation field, cavity quantum electrodynamics (QED) induces EM radiation at that frequency to be emitted from the bubble wall. Subsequently, the emitted EM radiation is absorbed. But cavity QED inhibits the spontaneous emission of any EM radiation absorbed at a frequency lower than the current bubble resonant frequency. Instead, the absorbed EM radiation may accumulate to be released as SL photons or it may be converted to free electrons either directly by the photoelectric effect or indirectly by the microwaves generated as the bubble collapses. By any combination of these processes, the collective EM radiation in the bubble wall is effectively focused on the gases within the bubble in the manner of a variable frequency UV to soft X-ray laser. A limited number of deuterium-deuterium (D-D) fusion events is suggested for ambient temperatures near the freezing point. Planck energies in excess of 10 keV/D2O vapor molecule are found as the D's in the low-density plasma are forced together under bubble wall collision pressures of ~200 atm. For a 20-kHz acoustic drive frequency, the thermal heating is of the order of a few microwatts, but neutrons should be detectable.