Selective excitation of erbium in silicon-infiltrated silica colloidal photonic crystals

Optically active erbium ions in the silica and silicon sections of a Si-infiltrated silica colloidal photonic crystal can be separately addressed. A face-centered cubic colloidal crystal composed of 860 nm silica colloids was made by self-assembly under controlled drying conditions. It was then infiltrated with Si using chemical vapor deposition at 550 °C. Next, the photonic crystal was doped with erbium ions by 2 MeV ion implantation. The erbium ions were activated by thermal anneals at 400 and 750 °C, and showed clear photoluminescence at 1.5 μm in both the Si and silica parts of the photonic crystal. By varying measurement temperature and excitation wavelength the erbium ions were selectively excited in Si and/or silica. In this way the local optical density of states in these photonic crystals can be selectively probed. The emission linewidth for Er3+ in crystalline Si is relatively narrow and fits well within the calculated photonic band gap. The long luminescence lifetime of Er in Si makes these photonic crystals an ideal geometry to measure effects of the optical density of states on spontaneous emission.