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Monolithic polychromatic light-emitting diodes (LEDs) based on micro-structured InGaN/GaN quantum wells are demonstrated. The microstructure is created through regrowth on SiO2 mask stripes along the [1100] direction and consists of (0001) and {1122} facets. The LEDs exhibit polychromatic emission, including white, due to the additive color mixture of facet-dependent emission colors. Altering the growth conditions and mask geometry easily controls the apparent emission color. Furthermore, simulations predict high light extraction efficiencies due to their three-dimensional structures. Those observations suggest that the proposed phosphor-free LEDs may lead to highly efficient solid-state lighting in which the color spectra of light sources are synthesized to satisfy specific requirements for illuminations.

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We report on long-lasting afterglow phosphorescence at around 500 nm in Ce3+-doped yttrium scandium gallium garnet (YSGG) ceramics with the composition of (Y0.995Ce0.005)3Sc2Ga3O12 prepared by solid-state reaction at 1600 °C. The afterglow luminescence was observed for 1 h after the 440 nm excitation in the Ce:YSGG ceramic prepared under vacuum. However, the afterglow decay time decreased after O2 annealing. Therefore, one of the potential traps can be oxygen vacancies. Based on the correlation between the 5d levels and the conduction band, we present an afterglow mechanism and propose a new persistent phosphor under white light emitting diode (LED) illumination.

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