Forster transfer and the local optical density of states in erbium-doped silica

dOptically excited erbium ions incorporated near the surface of a silica glass decay by spontaneous emission and-at high Er concentration-via Forster energy transfer to quenching sites. By externally modifying the photonic microstructure we vary the local optical density of states (LDOS) in samples with different degrees of Forster transfer. Changes in spontaneous emission rate are consistent with calculated variations in LDOS at 1.5 mu m, while Forster energy transfer is not affected by the LDOS. The latter is attributed to the fact that Forster transfer involves virtual photons with a broad energy spectrum, excluding a special role for the LDOS at the atom's transition frequency.