Spontaneous emission rates of a single-impurity molecule in biaxial host crystals

The single molecule spectroscopy provides the possibility to measure the spectra of a single impurity molecule, whereby the influence of the inhomogeneous structure of the host are eliminated. The main object of studies in the single molecule spectroscopy is the zero-phonon line - the narrowest and the most intense line in the spectrum. We have taken into account a factor which up to now has not been considered in the theories of zero-phonon line - the influence of the anisotropy of the host crystal on the spontaneous emission rate of the single-impurity molecule and thus also on the radiative line width. The relative spontaneous emission rate of the dipole transition of single-impurity molecules in biaxial crystals is determined through a formula with two coefficients. These coefficients are calculated as the functions of the difference of the principal refractive indexes n3−n2 for values of the principal refractive indexes 1.5⩽n1⩽1.7 and 1.55⩽n2⩽1.95.