We observed varying thermal quenching behavior of the yellow luminescence band near 2.2 eV in different GaN samples. In spite of the different behavior, the yellow band in all the samples is caused by the same defect—the YL1 center. In conductive n-type GaN, the YL1 band quenches with exponential law, and the Arrhenius plot reveals an ionization energy of ∼0.9 eV for the YL1 center. In semi-insulating GaN, an abrupt and tunable quenching of the YL1 band is observed, where the apparent activation energy in the Arrhenius plot is not related to the ionization energy of the defect. In this case, the ionization energy can be found by analyzing the shift of the characteristic temperature of PL quenching with excitation intensity. We conclude that only one defect, namely, the YL1 center, is responsible for the yellow band in undoped and doped GaN samples grown by different techniques.

a b s t r a c tThe abrupt and tunable quenching of photoluminescence (PL) in bulk ZnO samples is reported, a phenomenon which has been previously observed only in GaN and a few phosphorescent materials. ZnO samples grown by the hydrothermal method contain Li defects responsible for the orange luminescence (OL) band with a maximum at 2.0 eV. The Li Zn acceptor is well studied, but there is some disagreement in the literature on the value of its ionization energy. Here we show that the ionization energy of the Li Zn acceptor responsible for the OL band is 0.65 70.10 eV. The thermal emission of holes from the Li Zn acceptor to the valence band and their subsequent capture by unknown nonradiative centers causes the abrupt quenching of PL, the temperature of which is tunable by excitation intensity.Published by Elsevier B.V.

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