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ABSTRACT: An intense broadband and flat 1.3 μ m emission from Bi-doped germanate glass has been measured upon excitation with a commercial laser diode, which makes the glasses more attractive for their use in broadband optical fiber amplifiers. The 1.3 μ m emission exhibits a distinctive fine luminescence shape with four bands centered at 1225, 1320, 1370, and 1390 nm, respectively. It is noted that the addition of CeO <sub>2</sub> (2 mol %) , As <sub>2</sub> O <sub>5</sub> (2 mol %) , or Y <sub>2</sub> O <sub>3</sub> (1 mol %) into Bi-doped glasses could remarkably enhance the luminescence intensity by a factor of 4, 12, and 23, respectively. Whereas, no luminescence has been observed for the glass prepared under a controlled redox condition. The optical properties of the Bi-doped glasses and the possible mechanism involved have been explained.
Journal of Applied Physics 09/2008; · 2.17 Impact Factor
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ABSTRACT: Centralized control using the wide-area information has been suggested to enhance the dynamic performance of large interconnected power systems. According to the inverse system method and LQR optimal control theory, this paper presents a nonlinear hierarchical global controller based on the wide-area information including the on-line measured center of rotor angle and total unbalanced power. Moreover, it has been verified that the optimal control in the sense of linear quadratic state regulator principle for the linearized system is equivalent to an optimal control in the sense of extended quadratic output regulator performance index for the primitive nonlinear system. So, the designed controller is an optimal controller for the nonlinear system digital simulation demonstrates that the multi-machine power system under the nonlinear global control has less settling time, swing times, oscillatory peak value and more critical clearing time and better voltage stability performance than that under PID control and nonlinear decentralized control.
Developments in Power System Protection, 2008. DPSP 2008. IET 9th International Conference on; 04/2008
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ABSTRACT: An efficient near-infrared (NIR) quantum cutting (QC) in Gd Al <sub>3</sub>( B O <sub>3</sub>)<sub>4</sub>: RE <sup>3+</sup>, Yb <sup>3+</sup> ( RE = Pr , Tb, and Tm) phosphors has been demonstrated, which involves the conversion of the visible photon into the NIR emission with an optimal quantum efficiency approaching 200%, by exploring the cooperative downconversion mechanism from RE <sup>3+</sup> ( RE = Pr , Tb, and Tm) excitons to the two activator ions, Yb <sup>3+</sup> . The development of NIR QC phosphors could open up a new approach in achieving high efficiency silicon-based solar cells by means of downconversion in the visible part of the solar spectrum to ∼1000 nm photons with a twofold increase in the photon number.
Applied Physics Letters 08/2007; · 3.84 Impact Factor
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ABSTRACT: We report an intense room-temperature blue upconversion in Tm <sup>3+</sup>/ Yb <sup>+3</sup> -codoped Ga <sub>2</sub> O <sub>3</sub>– GeO <sub>2</sub>– Bi <sub>2</sub> O <sub>3</sub>– PbO ( PbF <sub>2</sub>) glasses upon excitation with a convenient 980 nm laser diode. Effects of PbF <sub>2</sub> doping on the thermal stability, structure, and upconversion properties of Tm <sup>3+</sup>/ Yb <sup>3+</sup> -codoped gallate-germanium-bismuth-lead glasses have been investigated. We find that the presence of PbF <sub>2</sub> provides two potentials: shortening the ultraviolet cutoff band and decreasing the phonon energy of host glasses. The blue-upconversion intensity has a cubelike dependence on incident pump-laser power, indicating a three-photon process. Energy-transfer process and nonradiative phonon-assisted decay could be responsible for the population of the <sup>1</sup>G<sub>4</sub> emitting level of the Tm <sup>3+</sup> . The results indicate the potential possibility towards the development of an oxide-based blue-upconversion glass-fiber laser.
Journal of Applied Physics 03/2006; · 2.17 Impact Factor
