Enhancement of Luminescence Efficiency of Y2O3 Nanophosphor via Core/Shell Structure.

We successfully fabricated Y2O3:RE3+ (RE = Eu, Tb, and Dy) core and core-shell nanophosphors by the molten salt method and sol-gel processes with Y2O3 core size of the order of 100~150 nm. The structural and morphological studies of the RE3+-doped Y2O3 nanophosphors are analyzed by using XRD, SEM and TEM techniques, respectively. The concentration and annealing temperature dependent structural and luminescence characteristics were studied for Y2O3:RE3+ core and core-shell nanophosphors. It is observed that the XRD peaks became narrower as annealing temperature increased in the core-shell nanophosphor. This indicates that annealing at higher temperature improves the crystallinity which in turn enhances the average crystallite size. The emission intensity and quantum yield of the Eu3+-doped Y2O3 core and core-shell nanoparticles increased significantly when annealing temperature is varied from 450 to 550 °C. No considerable variation was noticed in the case of Y2O3:Tb3+ and Y2O3:Dy3+ core and core-shell nanophosphors.

Engineering of TeO2-ZnO-BaO-Based Glasses for Mid-Infrared Transmitting Optics.

In this paper, the glass systems, TeO2-ZnO-BaO (TZB), TeO2-ZnO-BaO-Nb2O5 (TZB-Nb) and TeO2-ZnO-BaO-MoO3 (TZB-Mo), were fabricated by the traditional melt-quench protocol for use as mid-infrared (mid-IR) transmitting optical material. The effect of Nb2O5 and MoO3 on the key glass material properties was studied through various techniques. From the Raman analysis, it was found that the structural modification was clear with the addition of both Nb2O5 and MoO3 in the TZB system. The transmittance of studied glasses was measured and found that the optical window covered a region from 0.4 to 6 µm. The larger linear refractive index was obtained for the Nb2O5-doped TZB glass system than that of other studied systems. High glass transition temperature, low thermo-mechanical coefficient and high Knoop hardness were noticed in the Nb2O5-doped TZB glass system due to the increase in cross-linking density and rigidity in the tellurite network. The results suggest that the Nb2O5-doped TZB optical glasses could be a promising material for mid-infrared transmitting optics.

Temperature and Vibration Dependence of the Faraday Effect of Gd2O3 NPs-Doped Alumino-Silicate Glass Optical Fiber.

All-optical fiber magnetic field sensor based on the Gd2O3 nano-particles (NPs)-doped alumino-silicate glass optical fiber was developed, and its temperature and vibration dependence on the Faraday Effect were investigated. Uniformly embedded Gd2O3 NPs were identified to form in the core of the fiber, and the measured absorption peaks of the fiber appearing at 377 nm, 443 nm, and 551 nm were attributed to the Gd2O3 NPs incorporated in the fiber core. The Faraday rotation angle (FRA) of the linearly polarized light was measured at 650 nm with the induced magnetic field by the solenoid. The Faraday rotation angle was found to increase linearly with the magnetic field, and it was about 18.16° ± 0.048° at 0.142 Tesla (T) at temperatures of 25 °C-120 °C, by which the estimated Verdet constant was 3.19 rad/(T∙m) ± 0.01 rad/(T∙m). The variation of the FRA with time at 0.142 T and 120 °C was negligibly small (-9.78 × 10-4 °/min). The variation of the FRA under the mechanical vibration with the acceleration below 10 g and the frequency above 50 Hz was within 0.5°.

UV Photoluminescence of Alumino-Germano-Silicate Glass Optical Fiber Incorporated with Gd2O3 Nano-Particles Upon Illumination of Xenon-Lamp.

Alumino-germano-silicate glass optical fiber incorporated with Gd2O3 nano-particles (NPs) was developed by using the modified chemical vapor deposition and the drawing process. The formation of spherical Gd2O3 NPs in the fiber core with average diameter of 10.8 nm was confirmed by the TEM. The distinct absorption peaks in the fiber preform appearing in the UV region at 205, 247, 253, 274, and 312 nm were due to the incorporated Gd2O3 NPs via reorganization of the seven 4f electrons into various multiplets of Gd ions. In the case of the optical fiber obtained by drawing of the preform at high temperature about 2150 °C, absorption peaks due to Gd2O3 NPs were found to appear at 383 and 455 nm, which were red-shifted from 274 and 312 nm of the preform, respectively, and it may be due to increase in the size of Gd2O3 NPs after the drawing process. To investigate the photoluminescence (PL) property for UV sensor applications, the PL of the fiber was obtained by illumination of the Xenon-lamp. A PL band appeared in the wavelength band from 370 nm to 450 nm, centering at about 400 nm, which can be attributed to the presence of Gd2O3 NPs embedded in the fiber core. It was also found that the PL intensity at 400 nm showed linear dependence with the excitation power from 0 to 400 W.

Infrared-to-Visible Light Conversion in Er(3+) -Yb(3+) :Lu3 Ga5 O12 Nanogarnets.

Er(3+) -Yb(3+) co-doped Lu3 Ga5 O12 nanogarnets were prepared and characterized; their structural and luminescence properties were determined as a function of the Yb(3+) concentration. The morphology of the nanogarnets was studied by HRTEM. Under 488 nm excitation, the nanogarnets emit green, red, and near-infrared light. The decay curves for the ((4) S3/2 , (2) H11/2 ) and (4) F9/2 levels of the Er(3+) ions exhibit a non-exponential nature under resonant laser excitation and their effective lifetimes are found to decrease with an increase in the Yb(3+) concentration from 1.0 to 10.0 mol %. The non-exponential decay curves are well fitted to the Inokuti-Hirayama model for S=8, indicating that the mechanism of interaction for energy transfer between the optically active ions is of dipole-quadrupole type. Upon 976 nm laser excitation, an intense green upconverted emission is clearly observed by the naked eyes. A significant enhancement of the red-to-green intensity ratio of Er(3+) ions was observed with an increase in Yb(3+) concentration. The power dependence and the dynamics of the upconverted emission confirm the existence of two-photon upconversion processes for the green and red emissions.