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Rose Bengal was spun on spherical gold nanoparticles immobilized on a quartz plate by a silane coupling agent. The enhancement of the dye fluorescence was studied by changing the diameter of the gold nanoparticles from 20 to 250 nm. A maximum enhancement of dye fluorescence was observed at a size of 100 nm. We found good agreement between the experimental result and the theoretical calculation. From the theoretical analysis it is suggested that the maximum enhancement is obtained when the incident light and fluorescence light are in optimum resonance with the surface plasmons in the gold nanoparticles. These results demonstrate that the control of particle size is extremely important to obtain an optimum enhancement of dye fluorescence caused by metal particles.

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We report a breakthrough in the search for versatile diffractive elements for cold neutrons. Nanoparticles are spatially arranged by holographical means in a photopolymer. These grating structures show remarkably efficient diffraction of cold neutrons up to about 50% for effective thicknesses of only 200 m. They open up a profound perspective for next generation neutron-optical devices with the capability to tune or modulate the neutron diffraction efficiency.

We reported the preparation of bright and multicolor luminescent colloidal Si nanocrystal (Si-nc) by pulsed UV laser irradiation to porous Si (PSi) in an organic solvent. The different-luminescence-color (different-sized) colloidal Si-nc was produced by the pulsed laser-induced fragmentation of different-sized porous nanostructures. The colloidal Si-nc samples were found to have higher photoluminescence quantum efficiencies (20%–23%) than the PSi samples (1%–3%). The brighter emission of the colloidal Si-nc was attributed to an enhanced radiative band-to-band transition rate due to the presence of a surface organic layer formed by UV laser-induced hydrosilylation.

Rb-based hexafluoride red-emitting phosphors, Rb 2 SiF 6 :Mn 4+ and Rb 2 TiF 6 :Mn 4+ , were synthesized by the coprecipitation method. Optical microscopy observation, X-ray diffraction (XRD) measurement, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and luminescence decay characteristics measurements were used to study the structural and optical properties of the phosphors. The photographs of the bulk samples showed clear crystallographic habits originating from the cubic and trigonal symmetries of the Rb 2 SiF 6 and Rb 2 TiF 6 hosts, respectively, in agreement with the XRD results. The phosphors exhibited an intense narrow-band Mn 4+ ( 2 E g → 4 A 2g ) red emission with internal quantum efficiencies higher than 90% upon blue light excitation. The Franck−Condon analysis of the PLE data yielded the Mn 4+ intra-d-shell transitions to occur at ∼2.47 eV (∼2.34 eV) for the 4 A 2g → 4 T 2g transition and at ∼2.86 eV (∼2.83 eV) for the 4 A 2g → 4 T 1g transition in the Rb 2 SiF 6 :Mn 4+ (Rb 2 TiF 6 :Mn 4+ ) phosphor. Temperature dependence of the PL spectra from T = 20 to 500 K gave the quenching temperature values (T q 's) at which the PL intensity has fallen to half its maximum value to be T q ∼ 490 and ∼450 K for Rb 2 SiF 6 :Mn 4+ . To the best of our knowledge, only one paper has been published on Rb 2 TiF 6 reporting that it crystallizes in the trigonal structure with a = 0.5892 nm and a = 0.4795 nm. Our synthesized phosphors were examined by the X-ray diffraction (XRD) measurement, PL, PLE, and PL decay curve measurements. Temperature dependence of the PL properties was also examined from T = 20 to 500 K in 10-K increments. Efficient sharp red emissions with internal quantum efficiencies larger than 90% were observed from our phosphors that may promise improving a color rendering index of the conventional white-LED lamps.z E-mail: tnakamura@gunma-u.ac.jp; adachi@gunma-u.ac.jp ExperimentalThe rubidium hexafluorometallate phosphors were grown by the coprecipitation method. First, XO 2 (X = Si, Ti) and Rb 2 CO 3 in molar ratio of 1 : 1 were dissolved in an HF solution. Then, KMnO 4 powder was added in the HF solution at 300 K. This mixed solution was left in dark for a few days and resulted in a large single-crystalline phosphor growth (see Fig. 2 below). The resultant bulk single-crystalline phosphors were paper-filtered and dried in room ambient. They were grained in an agate mortar and then used for various measurements.The crystal structures of the synthesized phosphors were examined by performing an XRD analysis using a SmartLab X-ray diffractometer (Rigaku) with Cu Kα radiation at λ = 0.1542 nm. PL measurements were carried out using a single monochromator equipped with a charge-coupled device (Princeton Instruments PIXIS 100) in a CryoMini cryostat (Iwatani Industrial Gases) and a stainless cryostat (Technolo Kogyo) at T = 20 − 500 K in increments of 10 K. A He−Cd laser at λ ex = 325 nm (Kimmon IK3302R-E) was used as the excitation light source.PLE measurements were performed at 300 K...

We examine thermal distortions of volume holograms recorded in (meth)acrylate photopolymers doped with SiO(2) or ZrO(2) nanoparticles. A holographic method is used to evaluate the temperature-induced Bragg-angle detuning of recorded volume holograms as a result of thermally induced refractive index and dimensional changes. It is found that the incorporation of inorganic nanoparticles into photopolymer leads to the effective suppression of these thermal changes, thereby extending the range of operating temperatures for their use in photonic applications.