Measuring and Modifying the Spontaneous Emission Rate of Erbium near an Interface

Erbium implanted sodalime silicate glass was covered with a range of transparent liquids. The spontaneous emission rate of ${\mathrm{Er}}^{3+}$ around 1.54 $\mu$m shows clear changes depending on the liquid refractive index and Er depth. A rigorous quantum mechanical calculation shows that the effect of the interface on the spontaneous emission rate is fully described by the classical density of optical modes as a function of distance from the interface. The data provide the first direct determination of the radiative transition rate $\left(45s^{-1\mathrm{}}\right)$ at 1.54 $\mu$m of ${\mathrm{Er}}^{3+}$ which is widely used in optical amplifiers.