Significant suppression of spontaneous emission in SiO2 photonic crystals made with Tb3+-doped LaF3 nanoparticles

SiO2 inverse opals made with LaF3:Tb3+ nanoparticles were fabricated. The spontaneous emission lifetime of the D-5(4) -> F-7(4) transition of Tb3+ ions at 542 nm embedded in the SiO2 inverse opal structure was determined. In contrast to an average lifetime of 2.8 ms in photonic crystals when the photoluminescence of the Tb3+ envelop was located outside the photonic stop band, a lifetime of 4.0 ms was observed when the Tb3+ photoluminescence fully overlaps with the photonic stop band in the inverse opal. The obtained results demonstrate that the photonic structure affects the spontaneous emission significantly, resulting in a 40% increase of the luminescence lifetime of Tb3+ ions. In other words, the density of optical states is reduced at the emission frequency of Tb3+ (i.e., 542 nm) which reduces the radiative rate constant.