Visible to infrared energy conversion in Pr3+-Yb3+ co-doped fluoroindate glasses

Processes involving visible to infrared energy conversion are presented for Pr3+-Yb3+ co-doped fluoroindate glasses. The emission in the visible and infrared regions, the luminescence decay time of the Pr 3+:3P0 → 3H4 (482 nm), Pr3+:1D2 → 3H6 (800 nm), Yb3+:2F5/2 → 2F 7/2 (1044 nm) transitions and the photoluminescence excitation spectra were measured in Pr3+ samples and in Pr3+-Yb 3+ samples as a function of the Yb3+ concentration. In addition, energy transfer efficiencies were estimated from Pr3+: 3P0 and Pr3+:1D2 levels to Yb3+:2F7/2 level. Down-Conversion (DC) emission is observed due to a combination of two different processes: 1-a one-step cross relaxation (Pr3+:3P0 → 1G4; Yb3+:2F7/2 → 2F5/2) resulting in one photon emitted by Pr3+ (1G4 → 3H5) and one photon emitted by Yb3+ (2F7/2 → 2F5/2); 2-a resonant two-step first order energy transfer, where the first part of energy is transferred to Yb3+ neighbor through cross relaxation (Pr3+:3P0 → 1G4; Yb3+:2F7/2 → 2F5/2) followed by a second energy transfer step (Pr 3+:1G4 → 3H4; Yb3+:2F7/2 → 2F5/2). A third process leading to one IR photon emission to each visible photon absorbed involves cross relaxation energy transfer (Pr3+: 1D2 → 3F4; Yb 3+:2F7/2 → 2F5/2). © 2013 Elsevier B.V. All rights reserved.

Feed digestibility and productive performance of bullfrogs raised in cages and fed in different periods and high frequency

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Polyculture of frogs and tilapia in cages with high feeding frequency

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Frequency tunable continuous THz wave generation in a periodically poled fiber

An all-fiber approach to terahertz generation using a periodically poled optical fiber is proposed and experimentally demonstrated. In the proposed approach, a continuous-wave THz wave is generated at a periodically poled fiber by beating two optical wavelengths from two laser sources with the wavelength spacing corresponding to the frequency of the THz wave. The key component in the system is the periodically poled fiber, which is made by a twin-hole fiber with the fiber core residing between two holes. The twin-hole fiber is then thermally poled at a temperature of similar to 260 degrees C with a voltage of 3.3 kV applied to the silver electrodes inside the two holes to introduce second-order nonlinearity. The quasi phase matching (QPM) condition is achieved by periodically erasing the thermal poling induced second-order nonlinearity with an ultraviolet laser, which enhances the energy conversion efficiency. The proposed approach is validated by an experiment. The emission of a THz wave centered at 3.8 THz with an output power of 0.5 mu W is observed. The frequency tunability between 2.2 and 3.8 THz is also experimentally demonstrated.

Frequency upconversion involving triads and quartets of ions in a Pr3+/Nd3+ codoped fluoroindate glass

Frequency upconversion (UC) processes involving energy transfer (ET) among Nd 3+ and Pr 3+ ions in a fluoroindate glass are reported. In a first experiment, the excitation of Pr 3+ [transition 3H 4→ 1D 2] and of Nd 3+ [transition 4I 9/2→( 2G 7/2+ 4G 5/2)] was achieved with a dye laser operating in the 575-590 nm range. In a second experiment, the Nd 3+ ions were excited with the second harmonic of a Nd: YAG laser at 532 nm. The ET processes leading to UC in both experiments were studied by monitoring the blue fluorescence decay at 480 nm due to the transition 3P 0→ 3H 4 in Pr 3+. In the more relevant UC process, quartets of ions (Nd-Nd-Pr-Pr) are excited due to absorption of three laser photons by two Nd 3+ ions which transfer their energy to two Pr 3+ ions. Each Pr 3+ ion promoted to the 3P 0 level decays to the ground state emitting one photon in the blue region. This conclusion was achieved investigating the dependence of the UC fluorescence intensity as a function of laser intensity, samples concentrations, and temporal behavior of the UC signal. Other UC processes involving nonisoionic groups of three ions are also reported. © 2002 American Institute of Physics.