Fabrication of ZnO nanoparticles by laser ablation in liquid medium is reported. The possibility of using a sintered ZnO target for the ablation as well as a Zn plate is demonstrated. The appropriate aqueous solution of sodium dodecyl sulfate is found to be 1 mM for ZnO growing. The shape of ZnO nanoparticles is sphere and its diameter is 30 ∼ 60 nm. Fourier transform infrared spectra, Raman scattering spectra, and photoluminescence spectra reveal the optical properties of ZnO nanoparticles. Nanoparticles obtained by using ZnO targets show a smaller defect density compared with those by using Zn targets.
We synthesized Cr3+, Cr4+-codoped Mg2SiO4 phosphors and studied their optical properties for application as a novel wideband near-infrared (NIR) light-source. The phosphors have an ultra-wideband NIR luminescence spectrum of 650–1400 nm. The origin should be the
transition of Cr3+ and the
transition of Cr4+. The luminescence spectrum spans over one octave range and covers the “optical window in biological tissues”. We successfully achieved an ultra-wideband luminescence of 650–1400 nm with a maximum output power of 367.5 μW by combining a blue LED with Cr3+ and Cr4+-codoped Mg2SiO4 phosphors in a single package.
Excitation wavelength dependence of red persistent luminescence in phosphor is reported. Persistent luminescence appears under visible light excitation in the wavelength region of 400–600 nm. Photon energy from white light-emitting diode lamps is possibly stored in this material. This sulfide phosphor is synthesized using iodine vapor. Under iodine vapor, Eu2+ and Tm3+ are found to be efficiently included in CaS. The concentration dependence of Eu2+ is studied, and the optimum concentration is 0.05%. Trap depth of 0.27–0.33 eV contributing to persistent luminescence is evaluated by using thermoluminescence.
Structural and optical properties of Ba1−x
Eu
x
Si2S5 are investigated for 0 ⩽ x ⩽ 1. A monoclinic structure similar to SrSi2S5 is maintained for the whole range of x. With the increase in x, continuous and isotropic decrease of lattice constants appears because of the replacement of Ba2+ by smaller Eu2+. Raman and infrared absorption spectra show the existence of
anions in BaSi2S5. Green photoluminescence (PL) originating from the 4f65d–4f7 transition of Eu2+ is obtained. The maximum PL efficiency of 52% is found for x = 0.01. Wavelength variation of the PL peak between 500 and 524 nm for 0.01 ⩽ x ⩽ 0.9 can be understood by the presence of two Eu2+ sites having different decay times in Ba
x
Eu1−x
Si2S5. Green PL and electroluminescence are obtained from (Ba,Eu)Si2S5 fabricated on silicon substrate.
We report the fabrication of europium thiosilicate (Eu 2 SiS 4 ) 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. Eu 2 SiS 4 shows intense yellow photoluminescence, and its wavelength (peak 570 nm) and width (60 nm) are reproducible. This corresponds to the 4f 6 5d-4f 7 transition of Eu 2þ . The photoluminescence efficiency of Eu 2 SiS 4 is measured and estimated to be 0.5%.
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