Radiative lifetime modification of LaF₃:Nd nanoparticles embedded in 3D silicon photonic crystals.

IO N Control of spontaneous emission (SE) is central to many applications involved with photon management including light emitting sources, [ 1–3 ] solar energy [ 4 , 5 ] and quantum information processing. [ 6 , 7 ] For example, control of the direction of SE may facilitate more effi cient light extraction in optical display devices. Spectral redistribution of SE may permit more photons to couple into useful optical modes in optical cavity devices (e.g. lasers). According to Fermi’s golden rule, the rate of SE is governed by the number of available electromagnetic modes and the coupling between the electric fi eld and the emission dipole at the location of the emitter, namely, local density of states (LDOS). [ 8 ] Therefore, key to the manipulation of SE is full control of the photonic DOS. Photonic crystals (PhCs), materials with periodically varying refractive index on a length scale comparable to the wavelength of light, provide an excellent means to modify the photonic DOS. [ 4 , 9 ] In analogy to Bragg diffraction of electrons in atomic crystals, photons with a specifi c range of energies (the so called stopgap) cannot propagate along certain directions in the PhC. [ 10 ] If the refractive index contrast between the two materials is large enough, stopgaps can exclude a substantial solid angle in the crystal, which results a decreased DOS at these photon energies. [ 11 ] In extreme cases, where a full photonic band gap (PBG) arises, light is forbidden to travel in all directions and the DOS vanishes at the PBG. [ 12–14 ] However, because the integrated number of photonic states over photon energies is conserved, the DOS is strongly enhanced at the edges of PBG and highly depleted within the PBG. [ 15 ] Thus, PhCs can be used to suppress SE within the PBG and enhance SE at the edge of PBG. Compared to 1D and 2D PhCs, which inherently cannot control SE in all three directions, 3D PhCs hold promise for complete control over SE. While various methods have been developed to realize 3D PhCs, [ 16 ] self-assembled 3D PhCs (so-called artifi cial opals), constructed by close-packed spheres in a face-centered cubic lattice, are attractive owning to their ease of fabrication and because their optical properties can be tuned simply by varying the sphere diameter. [ 17 ] Artifi cial opals made of polystyrene or silica can also be used as sacrifi cial templates