Ilgon Kim

Spectroscopic and structural studies of Sm2+ doped orthophosphate KSrPO4 crystal

Sm2+ ions doped KSrPO4 were prepared by high-temperature solid-state reaction method. The samples were investigated by x-ray powder diffraction, photoluminescence excitation and emission spectra, and luminescence decay measurements. After excitation into the 4f55d1 levels, the emission of Sm2+ ions showed D05→FJ7 (J=0,1,2) emission together with the broad 5d→4f emission band. The luminescence of Sm2+ ions was sensitive to the temperature. With the decreasing of the temperature, the broad 5d→4f emission band of Sm2+ ions gradually quenched, while D05→FJ7 (J=0,1,2) emission lines could be clearly detectable. Based on the luminescence properties of Sm2+ ions and structure of KSrPO4 crystal, the crystallographic sites and the energy structure correlated with 4f→5d transitions of Sm2+ ions in KSrPO4 were discussed.

X-ray-induced reduction of Sm3+-doped SrB6O10 and its room temperature optical hole burning

We prepared two kinds of Sm-doped strontium borates. When the samples were prepared in air environment, while the Sm3+ ions doped in strontium tetraborate (STB) were well reduced, the trivalent Sm ions were partially reduced in strontium hexaborate (SHB). The SHB was successfully reduced by subsequent x-ray irradiation (SHBX) and showed a strong Sm2+ emission. The photoluminescence, excitation spectrum and spectral hole burning experiments were conducted for the samples. The crystallographic sites of Sm2+ ions were found to be different in the STB and SHBX. Spectral holes were observed at room temperature in both samples STB and SHBX. The measured hole depths were 24% and 63% in STB and SHBX, respectively. As a result, we could obtain effective and novel hole burning material based on the Sm-doped strontium borates with x-ray-induced reduction.

Photo-luminescence properties of CuCl quantum dots and the dependence of biexciton formation rates on quantum dot sizes

We fabricated CuCl quantum dots (QDs) in a glass matrix. The blue shift of the exciton spectrum caused by quantum confinement effects was observed in the linear absorption and the photo-luminescence (PL) spectrum. Inhomogeneous line broadening was mainly induced by the size distribution of CuCl QDs and we found that the size distribution has Gaussian profiles. By solving the steady state rate equation, we also found that the intensities of biexciton PL were proportional to the square of exciton PL intensities, and the results were well accorded with the experimental results. The formation rates of biexciton were proportional to the volumes of CuCl QDs.

Optical properties of Eu3+ in yttrium oxide crystals prepared by a forced hydrolysis method

Optical properties and crystal structure of Y 2 O 3 powders doped with Eu 3+ ions were investigated through excitation and emission spectroscopy as well as X-ray diffraction. All samples exhibited ...

Optical Hole-Burning Properties of Sm2+-Doped Strontium Borates

Two kinds of Sm-doped Strontium Borates, SrB 4 O 7 (STB) and SrB 6 O 10 (SHB), were prepared for the spectral hole-burning experiment. Sm 3+ -ions doped into the STB were well reduced to Sm 2+ -ions in air environment. Though partial reduction was observed in SHB, the Sm 3+ -ions successfully reduced in the subsequent X-ray irradiation (SHBX). Permanent spectral hole-burning experiments were conducted for 7 F 0 – 5 D 1 transition band of Sm 2+ -ions. The two samples STB and SHBX showed deep spectral holes at room temperature and 50 K, i.e., 40 and 72% of hole depths in STB and SHBX at 50 K, respectively. The STB showed type I hole-burning properties and SHBX type II. The spectral holes were sustained for over 24 h at room temperature. Multiple holes were burnt in an inhomogeneously broadened band to demonstrate the optical data storage in the frequency domain.

Optical dephasing of Eu3+ in yttrium oxide crystals

Optical dephasing in a number of crystalline samples of Y 2 O 3 : Eu 3+ prepared by two different crystal-growth techniques were measured using two pulse photon echo method. For crystals prepared by a laser-heated pedestal growth, we report the dephasing rate, 1/ T m , at 1.4 K is up to two orders of magnitude faster than that previuosly reported for the flame fusion growth crystal. The spatial dependence of the optical dephasing rate, measured by TPPE (two-pulse photon echo), tells that the environments of echo producing ions at least highly depend on the spatial position which can not be detected by conventional laser spectroscopy techniques, suggesting two-pulse photon echo experiment can be served as a tool for probing the uniformity of the samples.

Temporal Behavior of Spectral Hole Depth and Influence of SnO on Spectral Hole Burning in CuCl Doped Glass

CuCl quantum dots (QDs) were fabricated in an aluminoborosilicate glass and hole burning experiment was performed by using the Littman type pulsed dye laser. The influence of SnO, which was added as a reducing agent, on hole burning was studied, and we found that there is almost no hole burning in SnO added sample. The dependence of the hole widths on the radius of QDs was studied, and the hole widths increased with decreasing average radius of QDs. Two kinds of hole burning processes occurred in CuCl doped glass. The hole burnt by a pulsed dye laser was partially recovered within 20 s, and then the remaining hole showed almost permanent life time at 8 K. The relationship between the hole burning process and the surface states and trapping sites in a glass matrix was also discussed.

Persistent spectral hole burning and optical properties of Sm2+ doped into Mg0.5Sr0.5FCl0.5Br0.5mixed crystal

We measured the temperature dependence of the fluorescence of Sm2+ ions doped into a Mg0.5Sr0.5FCl0.5Br0.5 mixed crystal and observed the persistent spectral hole burning at 90 K and 300 K. The electrons appearing at the 5D0→7 F0 transition mostly come via the 4f5d→5D1→5D0→7F0 route but some of the electrons come directly from the 4f5d band. At 90 K, persistent spectral hole burning was achieved much more efficiently by the photon-gated spectral hole-burning process than by the one-photon hole-burning process, while the one-photon hole-burning process is much more efficient at 300 K.