The effect of the dielectric medium upon the spontaneous emission rate was investigated using lead borate glass of various compositions lightly doped with the Eu${}^{3+}$ lanthanide ion. A dual approach used the variation of (i) electric dipole/magnetic dipole (ED/MD) emission rates from spectral integrations and (ii) absolute ED emission rates from lifetime measurements for comparison with the variation of the refractive index of the glass medium. Contrary to a previous study [Phys. Rev. Lett. 91, 203903 (2003)], the results show the relevance of the virtual-cavity model in this case. The MD emission rates were taken to follow the $n^3$ increase in density of photon states in the medium. The justifications for employing Eu${}^{3+}$ for identifying the appropriate model are given.

• Received 21 April 2011

DOI:https://doi.org/10.1103/PhysRevB.83.245123