Yasushi Nanai

Yellow Photoluminescence of Europium Thiosilicate on Silicon Substrate

We report the fabrication of europium thiosilicate (Eu2SiS4) on a silicon substrate. Europium sulfide (EuS) is thermally evaporated on a silicon substrate. It is sealed in a vacuum with sulfur and then heated at 650 °C. Eu2SiS4 shows intense yellow photoluminescence, and its wavelength (peak 570 nm) and width (60 nm) are reproducible. This corresponds to the 4f65d–4f7 transition of Eu2+. The photoluminescence efficiency of Eu2SiS4 is measured and estimated to be 0.5%.

Photoluminescence properties of erbium-doped europium thiosilicate

Photoluminescence properties of erbium-doped europium thiosilicate (Eu2SiS4 : Er) are reported. The material is fabricated in powder and on silicon substrates. The luminescence at 1.54 µm corresponding to the 4I13/2–4I15/2 transition of Er3+ is observed. Broad absorption of the 4f7–4f65d transition of Eu2+ in the host matrix in 350–500 nm region is used for the excitation of Er3+. Efficient energy transfer from the host to erbium is realized.

Crystal structure and optical properties of (Ba,Eu)2SiS4

Structural and optical properties of europium-doped barium thiosilicate are reported. The whole range of the Eu concentration x in Ba2(1−x)Eu2xSiS4 is studied. The lattice constants continuously decrease with the increase in x in the orthorhombic (0 ≤ x ≤ 0.6) or in the monoclinic (0.7 ≤ x ≤ 1) structures. This decrease changes the strength of the crystal field for Eu2+ and thus shifts the wavelength of photoluminescence (PL) (490–570 nm). For Eu-doped Ba2SiS4 (x = 0.01 and 0.02), the PL efficiency is 40%, and the decay time of its single exponential profile is obtained to be 240 ns. The decrease in the PL efficiency and the change in the decay profile (0.05 ≤ x ≤ 0.9) are explained by the enhancement of the cross relaxation among Eu2+ ions.

Luminescence Properties of Rare-Earth-Doped Thiosilicate Phosphors on Silicon Substrate

The luminescence properties of rare-earth-doped thiosilicate phosphors are reported. These thiosilicate materials are fabricated in phosphor layers on silicon substrates. For Eu2+-doped calcium thiosilicate, yellow (560 nm) and red (650 nm) bands are obtained in the photoluminescence spectrum, which is almost the same as that for the corresponding powder sample. The energy transfer efficiency from Eu2+ to Er3+ in Eu2SiS4:Er3+ on Si substrates is improved by optimization of the annealing conditions. In addition, the insulation of electroluminescence devices using BaSi2S5:Eu2+ on silicon-on-insulator substrates is improved using a high-dielectric-constant polymer as a transparent insulating layer.

Crystal structure and photoluminescence of (Gd,Ce)4(SiS4)3 and (Y,Ce)4(SiS4)3

Structural and photoluminescence (PL) properties of undoped and Ce3+-doped rare-earth thiosilicate (Gd1-xCex)4(SiS4)3 () and (Y1-xCex)4(SiS4)3 () are reported. They maintain a monoclinic structure (P21/n) for the whole range of x. Increases in lattice constants appear with the increase in x because of the replacement of Gd3+ and Y3+ by larger Ce3+. Yellow-orange PL originating from the 5d1-4f1 (2FJ, ) transition of Ce3+ is obtained. From the measurement of PL spectra at 20 K, red shifts of the peak wavelength with the increase in x would be understood by the change of relative intensity for two luminescent centers of Ce3+ in PL bands. The maximum internal quantum efficiency is 62% for (YCe)4(SiS4)3. These phosphors have higher water-resistance than alkaline-earth metal thiosilicate phosphors such as Ba2SiS4.

Luminescence Properties of Rare Earth-Doped Thiosilicate Phosphors on Silicon Substrate

Crystalline silicon (Si) is a key material in electronics and optelectronics devices. However, Si has no light emission at room temperature because of its indirect band gap. To develop silicon photonics and future optoelectoronics devices, the realization of e fficient silicon-based light sources at room temperature remains an important challenge. Phosphor materials including Si and rare earth ions have been studied for various light sources and displays. Up to now, silicate, silicon nitride, silicon oxynitride and thiosilicate materials were reported [1-5]. Especially, thiosilicate phosphors have advantages that relatively low temperature is necessary for fabrication and various luminescence wavelengths from blue to infrared region are reported [4-9]. From this viewpoint, the application of thiosilicate phosphors for light emitter on Si substrate should be examined. In this paper, photoluminescence (PL) properties of rare earth-doped thiosilicate phosphors are reported. The materials are fabricated in powder, and on silicon or silicon-on-insulator (SOI) substrates. E fficient visible and infrared luminescence from thiosilicate phosphor on Si substrates is observed. In addition, electroluminescence (EL) from BaSi 2 5:Eu on SOI substrates is realized. The result indicates that thiosilicate phosphor materials can be a light source on silicon-based substrates.