  We investigate consecutive absorption or emission of photons of the quantum
mechanical harmonic oscillator as a possible source of 1/f fluctuations.
Separating the absorption and emission process, we show that consecutively
absorbed or emitted photons give rise to an intermittent stochastic process;
thereby fluctuating clusters of photons are intermitted by distinct breaks. Let
the number of photons in a cluster be m and the cluster size distribution be
pm. We find that the intermittent process with a cluster size distribution pm
proportional to m-2 generates a pure 1/f spectrum. We show that 1/f
fluctuations are present in thermal equilibrium but average out to zero. As an
example we investigate phonons as a possible origin of 1/f fluctuations in an
extrinsic semiconductor. Acoustic phonons always produce a change in the
volume; this affects the donor ionization energy modulating also the g-r
process. We calculate the spectrum of such a modulated g-r process; thereby the
intermittent character of phonon activity is identified as the origin of 1/f
fluctuations. The Hooge parameter is found to depend on the mean number of
phonons comprised in a cluster, on the modulation depth of the g-r process and
on a factor which describes the temperature dependence of 1/f noise.
