Tae-Young Park

Optical properties of undoped and Ho3+, Er3+, and Tm3+-doped BaAl2S4 and BaAl2Se4 single crystals

The optical energy band gaps of BaAl2S4 and BaAl2Se4 single crystals at 300 K were found to be 3.98 and 3.35 eV, respectively, and the optical energy band gaps of Ho3+, Er3+, and Tm3+-doped BaAl2S4 and BaAl2Se4 single crystals were smaller than those of the undoped single crystals. Photoluminescence spectra peaked at 459 and 601 nm in the BaAl2S4 and at 486 and 652 nm in the BaAl2Se4. The photoluminescence emission peaks were attributed to donor–acceptor pair recombinations. Photoluminescence spectra of the Ho3+, Er3+, and Tm3+-doped BaAl2S4 and BaAl2Se4 at 5 K were measured in the wavelength range of 400–900 nm. Sharp emission peaks due to Ho3+, Er3+, and Tm3+ ions were observed and their transition mechanisms were proposed.

Optical properties of Ho3+-, Er3+-, and Tm3+-doped BaIn2S4 and BaIn2Se4 single crystals

BaIn 2 S 4 , BaIn 2 S 4 :Ho 3 + , BaIn 2 S 4 :Er 3 + , BaIn 2 S 4 :Tm 3 + , BaIn 2 Se 4 , BaIn 2 Se 4 :Ho 3 + , BaIn 2 Se 4 :Er 3 + , and BaIn 2 Se 4 :Tm 3 + single crystals were grown by the chemical transport reaction method. The optical energy gap of the single crystals was found to be 3.057, 2.987, 2.967, 2.907, 2.625, 2.545, 2.515, and 2.415 eV, respectively, at 11 K. The temperature dependence of the optical energy gap was well fitted by the Varshni equation. Broad emission peaks were observed in the photoluminescence spectra of the single crystals. They were assigned to donor-acceptor pair recombination. Sharp emission peaks were observed in the doped single crystals. They were attributed to be due to radiation recombination between the Stark levels of the Ho 3 + , Er 3 + , and Tm 3 + ions sited in C 1 symmetry.

Optical properties of MnAl2S4 and MnAl2Se4 single crystals

MnAl2S4 and MnAl2Se4 single crystals were grown by the chemical transport reaction method. Optical energy gaps of the MnAl2S4 and MnAl2Se4 single crystals were 3.75 and 3.21 eV, respectively, at 300 K. Emission peaks due to donor-acceptor pair recombinations were observed at 450 and 603 nm in the MnAl2S4 single crystal and at 488 and 655 nm in the MnAl2Se4 single crystal. Optical absorption peaks and emission peaks described as appearing due to Mn2+ ion sited in Td symmetry were observed at 414, 450, 482, and 527 nm in the MnAl2S4 single crystal and at 416, 455, 488, and 532 nm in the MnAl2Se4 single crystal.

Optical properties of undoped, Co2+- and Er3+-doped CdAl2Se4 single crystals

Abstract Single crystals of CdAl 2 Se 4 , CdAl 2 Se 4 :Co 2+ and CdAl 2 Se 4 :Er 3+ were grown by the chemical transport reaction method using iodine as a transporting material. The crystal structure of these single crystals has been shown to be a defect chalcopyrite, and the direct bandgap at 10 K has been found to be 3.082 eV for CdAl 2 Se 4 , 2.683 eV for CdAl 2 Se 4 :Co 2+ and 2.980 eV for CdAl 2 Se 4 :Er 3+ , respectively. We observed impurity optical absorption peaks due to electron transitions between the energy levels of Co 2+ ions sited at T d symmetry of the host material. We also observed two broad blue-green photoluminescence peaks centered at 458 and 539 nm in the photoluminescence spectrum at 10 K of CdAl 2 Se 4 single crystals. For CdAl 2 Se 4 :Er 3+ single crystals, on the other hand, sharp photoluminescence peaks were observed, which are due to emission transitions between the energy levels of Er 3+ ions with T d symmetry sites.

Photoluminescence spectra of Zn1−xCdxAl2S4 (0.0⩽x⩽0.2;0.8⩽x⩽1.0) single crystals

The photoluminescence spectra as well as the lattice constants and band gaps for the mixed single crystals Zn1−xCdxAl2S4 with 0.0⩽x⩽0.2 and 0.8⩽x⩽1.0 grown by the chemical transport reaction method were investigated. The Zn1−xCdxAl2S4 crystals were a cubic spinel phase α in the range of 0.0⩽x⩽0.2 and a defect chalcopyrite in the range of 0.8⩽x⩽1.0, and showed a miscibility range from x=0.2 to x=0.8 in the composition dependence of the lattice constants and band gaps. We observed two emission bands consisting of a strong blue emission band and a weak broad emission band due to donor-acceptor pair recombinations in the crystals with a cubic spinel and a defect chalcopyrite structure. These emission bands showed a different behavior in their temperature and composition dependence. An energy band scheme for the radiative mechanism of the Zn1−xCdxAl2S4 was proposed on the basis of our experimental results along with the measurements of photoinduced current transient spectroscopy and thermoluminescence.

Photoluminescence spectra of Er3+-doped MgAl2S4 and CaAl2S4 single crystals

MgAl2S4, CaAl2S4, MgAl2S4:Er3+ and CaAl2S4:Er3+ single crystals were grown by the chemical transport reaction method. The single crystals crystallized in an orthorhombic structure. The single crystals had the direct energy band structure and their optical energy gaps were 4.334 eV, 4.213 eV, 4.835 eV and 4.716 eV for the MgAl2S4, MgAl2S4:Er3+, CaAl2S4, and CaAl2S4:Er3+ single crystals, respectively, at 13 K. Sharp emission peaks appeared in the MgAl2S4:Er3+ and CaAl2S4:Er3+ single crystals, and they were interpreted to originate from the Er3+ ion substituted Mg2+ and Ca2+ ions in the MgAl2S4:Er3+ and CaAl2S4:Er3+ single crystals.

Photoluminescence Spectra of Zn 1- x Cd x Al 2 Se 4 Single Crystals

We investigated the photoluminescence spectra as well as the crystal structure and optical energy gaps of the Zn 1- x Cd x Al 2 Se 4 single crystals grown by the chemical transport reaction method. It was shown from the analysis of the observed x-ray diffraction patterns that these crystals have a defect chalcopyrite structure for a whole composition. The lattice constant a increases from 5.5561 A for x = 0.0 (ZnAl 2 Se 4 ) to 5.6361 A for x = 1.0 (CdAl 2 Se 4 ) with increasing x, whereas the lattice constant c decreases from 10.8890 A for x = 0.0 to 10.7194 A for x = 1.0. The optical energy gaps at 13 K were found to range from 3.082 eV ( x = 1.0) to 3.525 eV ( x = 0.0). The temperature dependence of the optical energy gaps was well fitted with the Varshni equation. We observed two emission bands consisting of a strong blue emission band and a weak broad emission band due to donor–acceptor pair recombination in the Zn 1- x Cd x Al 2 Se 4 for 0.0 ⩽ x ⩽ 1.0. These emission bands showed a red shift with increasing x. The energy band scheme for the radiative mechanism of the Zn 1- x Cd x Al 2 Se 4 was proposed on the basis of the photoluminescence thermal quenching analysis along with the measurements of photo-induced current transient spectroscopy. The proposed energy band model permits us to assign the observed emission bands.

Photoluminescence spectra of undoped and Er3+-doped MgAl2Se4 and CaAl2Se4 single crystals

MgAl2Se4, MgAl2Se4:Er3+, CaAl2Se4, and CaAl2Se4:Er3+ single crystals were grown by the chemical transport reaction method. The single crystals had the direct energy band gap and their optical energy gaps were 3.286, 2.855, 3.823, and 3.525 eV for the MgAl2Se4, MgAl2Se4:Er3+, CaAl2Se4, and CaAl2Se4:Er3+ single crystals, respectively, at 13 K. Broad photoluminescence spectra peaked at 477 and 672 nm for the MgAl2Se4 single crystal and at 459 and 633 nm for the CaAl2Se4 single crystal were obtained. Sharp emission peaks due to the Er3+ ion in the MgAl2Se4:Er3+ and CaAl2Se4:Er3+ single crystals were observed.