title: Directional study of the optical properties of Tb3+- and Eu3+-doped nanoparticles embedded in silica photonic crystals.
abstract: The effects of the stop band (SB) in colloidal photonic crystals composed of silica spheres containing Eu(3+)- and Tb(3+)-doped yttria nanoparticles are analysed. Reflection and transmission spectra indicate movement of the stop band, due to the 111 series of planes, towards shorter wavelengths with increasing angle of observation. The profile of the emission spectra is modified by the presence of the SB depending on the angle of measurement. Such a modification is more effective for a narrow emission band and it is thus more evident in the case of Tb(3+) than Eu(3+). An angular effect is also observed in the lifetime, which presents two maxima and one minimum. In the case of Tb(3+) the maxima are at observation angles of 35 and 50 degrees, and the minimum at 45 degrees. We attribute this behaviour to penetration of the excitation beam at 475 nm modulated by the stop band. The ions excited in this way emit from different depths in the crystal, and therefore their lifetime will be affected differently by the same stop band, depending on the thickness of the crystal that must be crossed. Eu(3+) shows a similar but less pronounced effect for two reasons: first, the main stop band (due to the 111 planes) is not effective at the excitation wavelength of 392 nm; second, the broadness of the Eu(3+) emission is comparable to the width of the SB, and a decrease in the transition rate at the wavelength of the SB maximum is compensated by an increase at the sides of the SB.
authors.affiliation: Chemistry Department, University of Victoria, PO BOX 3065 Victoria, BC, V8W 3V6, Canada.
authors.forename: Enrico
authors.initials: E
authors.lastname: Bovero
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Yano
authors.forename: Tadashi
authors.initials: T
authors.lastname: Nakamura
authors.forename: Yuri
authors.initials: Y
authors.lastname: Yamada
authors.forename: Frank C J M
authors.initials: FC
authors.lastname: van Veggel