Analysis of parasitic cyan luminescence occurring in GaInN blue light-emitting diodes J. Appl. Phys. 112, 074512 (2012) Gallium nitride-based light-emitting diodes with embedded air voids grown on Ar-implanted AlN/sapphire substrate Appl. Phys. Lett. 101, 151103 (2012) Analysis of the external and internal quantum efficiency of multi-emitter, white organic light emitting diodes

Optical properties of InxGa1−xN epitaxial layers with various indium compositions (x=0.02, 0.03, 0.05, 0.06, and 0.09) have been studied by means of temperature-dependent optical absorption and photoluminescence spectroscopy. A clear peak due to the absorption of InxGa1−xN ternary alloys was observed up to 300 K, which enabled us to investigate the temperature dependence of the Stokes shift. The Stokes shift at 4 K increased with an increase in the indium composition, and was estimated to be 22 and 45 meV for the samples with x=0.02 and 0.09, respectively. With an increase in temperature up to about 50 K, the Stokes shift increased slightly. With a further increase in temperature from 50 to 100 K, the Stokes shift decreased. Above 100 K, the Stokes shift was independent of the temperature and showed an almost constant value up to 300 K. The Stokes shift at 300 K was estimated to be 19 and 34 meV for the samples with x=0.02 and 0.09, respectively. This temperature dependence of the Stokes shift was characteristically common to all of the samples used in the present work, and was observed to be more prominent for the samples with higher indium compositions.

Structural and optical properties of europium-doped barium thiosilicate are reported. The whole range of the Eu concentration x in Ba2(1−x)Eu2x SiS4 is studied. The lattice constants continuously decrease with the increase in x in the orthorhombic (0 ⩽ x ⩽ 0.6) or in the monoclinic (0.7 ⩽ x ⩽ 1) structures. This decrease changes the strength of the crystal field for Eu2+ and thus shifts the wavelength of photoluminescence (PL) (490–570 nm). For Eu-doped Ba2SiS4 (x = 0.01 and 0.02), the PL efficiency is 40%, and the decay time of its single exponential profile is obtained to be 240 ns. The decrease in the PL efficiency and the change in the decay profile (0.05 ⩽ x ⩽ 0.9) are explained by the enhancement of the cross relaxation among Eu2+ ions.

Recombination dynamics of excitonic transitions in GaN homoepitaxial layers has been studied by means of time-resolved luminescence spectroscopy. An excitation-density-dependent transition of the dominant radiative recombination process at 3.471 eV from donor-bound excitons to biexcitons was clearly observed in the temporal behavior. In addition, double-exponential decay of biexciton luminescence was observed, which is one of the characteristics of biexciton luminescence at high excitation densities.

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