Publication date: 1 October 2016
Source:Thin Solid Films, Volume 616
Author(s): Housei Akazawa, Hiroyuki Shinojima
Photoluminescence from Eu3 + ions initiated by band-to-band excitations of ZnO host crystals was investigated in epitaxial films grown on sapphire C-planes. Emissions from Eu3 + ions were only observed when the films were deposited under H2 O vapor gas flow. The maximum emission intensities were three times as large as those of films deposited on Si substrates. Close correlation between the emission intensities of Eu3 + ions and disorder in the host crystal lattice was evidenced by X-ray diffraction, which indicates that non-radiative energy dissipation channels determine the lifetime of the excited states, and high crystallinity is essential for intense emissions. In addition, the emission intensities from ZnO defects and Eu3 + ions exhibited a similar dependence on annealing temperature, suggesting the relevance of defect-mediated energy transfer from ZnO to Eu3 + ions. The excitation energy is shared among band-edge emissions, defect emissions, and emissions from Eu3 + ions, and these emissions compete with one another. In particular, the overlap of the Eu3 + emission energies on the red defect emission band facilitates efficient energy transfer from the ZnO crystals. Hydrogen atoms released from H2 O will prevent Eu3 + ions from being bonded to excess oxygen atoms and/or promote substitution of Zn2 + sites with Eu3 + ions.
Source:Thin Solid Films, Volume 616
Author(s): Housei Akazawa, Hiroyuki Shinojima