Hong Lee Park

Two self-activated optical centers of blue emission in zinc gallate

Abstract The compositional dependence of the photoluminescence of ZnGa2O4 has been studied to identify the optical centers. In addition to the absorption band at 260 nm and the fluorescence band at 432 nm in ZnGa2O4 which is originated from self-activation center of the octahedral GaO groups in the spinel lattice, new absorption and fluorescence bands at 246 nm and 360 nm, respectively, have been observed. Ga3+ ions must be not only on the octahedral sites but also on the tetrahedral sites when the zinc gallate is synthesized with β-Ga2O3 and when it is annealed in an oxygen deficient atmosphere. Hence, the new self activated optical centers are due to the tetrahedral GaO groups in the spinel lattice. The incorporation of aluminum ion into the lattice, Zn(Ga1−xAlx)2O4, results in the blue shifts of the absorption and fluorescence bands of ZnGa2O4. This phenomenon is explained by the larger bandgap.

Photoluminescence of Eu3+ and Bi3+ in Na3YSi3O9

Abstract Optical characteristics of Eu3+ and Bi3+ in the Na3YSi3O9 host lattice have been studied. There is a single and highly symmetric site of Eu3+ ion in Na3YSi3O9 host lattice. The charge transfer state of Eu3+ ion lies in high-energy region close to the fundamental absorption domain of the host lattice. One absorption band for 1 S 0 → 3 P 1 transition of Bi3+ was found in Na3YSi3O9. The wavelength of maximum luminescence intensity of Bi3+ ( 3 P 1 → 1 S 0 ) is red-shifted as the Bi3+ concentration increases. Concentration quenching of the fluorescence from Bi3+ has been observed above 2 mol.% of concentration. Energy transfer between Eu3+ and Bi3+ is not efficient in this host due to the energy mismatch.

Fabrication of CdTe Quantum Dot Arrays on GaAs utilizng Nanoporous Alumina Masks

The uniformity and reproducibility of the CdTe QD arrays on the GaAs substrates can be improved by using a nanoporous mask. The CdTe QDs on the GaAs substrate were grown by a molecular beam epitaxy (MBE) method. The nanoporous alumina masks used for the fabrication of QD arrays have the thickness from 0.3 μm to 5 μm with the nanochannels of ~ 80 nm diameter and the pore density of ~ 10 10 cm -2 . When the thickness of the alumina mask used for the CdTe QD growth was about 300 nm, the CdTe QD arrays formed as a replica of the nanochannels of the mask. Smaller self-assembled CdTe QDs located randomly were produced by using the thicker nanochannel mask than 0.5 μm. The thickness of the nanochannel mask controls the size of the CdTe/GaAs QDs.