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Erbium doped optical materials have been widely researched and many applications have been demonstrated. According to the Fermi golden rule, the spontaneous emission rate from excited level |i> to
lower level |j> is Γij ∞ |Mij|2 ρ(νij), where Mij is the matrix element related to the two energy levels, ρij is the optical density and is also known as the photon mode density (PMD). The concept of PMD was put
forward by Purcell in 1946, and is a quantity determined by the environment aound the rare earth ions. The
radiative performance of a rare earth(RE) doped material is decided not only by the wave function of the
energy level that the rare earth ions are located, but also by the environment of the RE ions, i.e., the PMD. In
various materials, the state of the host (crystal, glass or glass ceramics), the composition of the host with same
state (for examples, the different glasses), the doping of metal into the host, and the surface plasmon portions
(SPP) arised from the metal gratings or nanoparticals on the host, will all change the optical density of the
materials, Thus the PMD are different. In this paper, we summarized the influence of the PMD on the
luminescence of erbium doped materials for above indicated cases. Especially, we reported the difference of
the luminescence performance of the erbium doped phosphate glass ceramics and its precursor glass, from
which, we can find that even the composition of both glass ceramics and glass are the same, the luminescence
performance are quite different due to the different PMD. Another example we illustrate in this paper is to use
SPP to change the PMD. When RE doped glass is coated with a thin metal film or islands, SPP mode will be
generated under special condition. We summarized the recent progress on the field, and also demonstrated the
enhancement of fluorescence in the visible wavelengths and 1.5μm wavelength, from which, we can think that
the SPP changes the PMD of the material and the emission rate is modified.
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