Simultaneous three-photon-excited violet upconversion luminescence of Ce3+: Lu2Si2O7 single crystals by femtosecond laser irradiation

We found that Ce3+:Lu2Si2O7 single crystals could be excited at 800 nm by using a femtosecond Ti:sapphire laser. The emission spectra of Ce3+:Lu2Si2O7 crystals were the same for one-photon excitation at 267 nm as for excitation at 800 nm. The emission intensity of Ce3+: Lu2Si2O7 crystals was found to depend on the cube of the laser power at 800 nm, consistent with simultaneous absorption of three 800 nm photons. The measured value of the three-photon absorption cross section is sigma'(3) = 2.44 x 10(-77) cm(6) s(2). (c) 2006 Optical Society of America.

Solution combustion synthesis, structure and luminescence of Y3Al5O12 : Tb3+ phosphors

The synthesis and optical properties of Y3Al5O12:Tb3+ phosphors are reported in this paper. Y3Al5O12:Tb3+ phosphors were synthesized by a facile solution combustion method. Citric acid traps the constituent cations and also acts as a fuel. Y3Al5O12 (YAG) phase can crystallize through sintering at 900 degrees C for 2 h, and there were no intermediate phases such as YAlO3 (YAP) and Y4Al2O9 (YAM) in the sintering process. The excitation spectra of crystalline Y3Al5O12:Tb3+ are different from that of amorphous one due to the crystal field effect. The emission spectra mainly show D-5(4) -> F-7(6) transition under UV excitation. The higher concentration quenching in Y3Al5O12:Tb3+ nanophosphors may be due to the confinement effect on resonant energy transfer of nanocrystalline. It is also indicated that the solution combustion synthesis method provides a good distribution of Tb3+ activators in Y3Al5O12 host. (c) 2005 Published by Elsevier B.V.

Blue upconversion luminescence generation in Ce3+: Gd2SiO5 crystals by infrared femtosecond laser irradiation

Blue frequency-upconversion fluorescence emission has been observed in Ce3+-doped Gd2SiO5 single crystals, pumped with 120-fs 800 nm IR laser pulses. The observed fluorescence emission peaks at about 440nm is due to 5d -> 4f transition of Ce3+ ions. The intensity dependence of the blue fluorescence emission on the IR excitation laser power obeys the cubic law, demonstrating three-photon absorption process. Analysis suggested that three-photon simultaneous absorption induced population inversion should be the predominant frequency upconversion mechanism. (c) 2006 Optical Society of America.

Cooperative and charge transfer luminescence in Yb3+ -doped yttrium aluminum perovskite (YAlO3)

YAlO3 (YAP) crystals with different Yb3+ concentration have been grown by Czochralski method and cooperative fluorescence of Yb3+ ions in YAP crystal was studied under 940-nm infrared (IR) LD excitation at room temperature. The Yb concentration dependence of absorption intensity of IR and charge transfer bands exhibit different features. The green emission band in the region of 480-520nm was assigned to the cooperative deexcitation of two Yb3+ ions. The remaining upconverted emission bands containing various sharp peaks associated with impurity ions were observed and discussed. Charge transfer luminescence of heavily doped 20at% Yb:YAP is strongly temperature dependent and no concentration quenching of the charge transfer luminescence was found through the investigation of different Yb levels samples. (c) 2006 Elsevier B.V. All rights reserved.

Spectral properties and charge transfer luminescence of Yb3+ : Gd3Ga5O12 (Yb : GGG) crystal

The Yb (10%):GGG and Yb (30%): GGG crystals have been grown by the Czochralski method. The chemical compositions are: Yb1.07Gd1.74Ga5.19O12 and Yb0.33Gd1.47Ga5.2O12. The absorption and emission spectra of Yb:GGG crystal at room temperature have been measured. The spectroscopic parameters of Yb:GGG and Yb:YAG have been compared. Optical absorption spectra of Yb:GGG show 4f-4f transitions related to Gd3+ ion around 300 nm, and also an onset of charge transfer (CT) transitions from oxygen ligands to Gd3+ or Yb3+ cations below 240nm. The CT absorption of Yb3+ is largely overlapped by that of Gd3+ ions. (c) 2005 Elsevier B.V. All rights reserved.

Visible luminescence in Yb3+-doped gadolinium gallium garnets

In this paper, some results on visible luminescence performed on Yb3+-doped gadolinium gallium garnets under 165 and 940 nm excitation were presented. The upconversion luminescence was ascribed to Yb3+ cooperative luminescence and the presence of rare earth impurity ions. The gain cross-sections of Yb:GGG crystal as a function of excited-state population fraction P were studied. Emission spectra under 165 nm at 20 K showed there was no charge transfer luminescence in Yb:GGG. (c) 2006 Elsevier B.V. All rights reserved.

Synthesis and luminescence characterization of cerium doped Lu2O3-Y2O3-La2O3 solid solution transparent ceramics

Ce3+:( Lu0.7Y0.25La0.05)(2)O-3 transparent ceramics were fabricated with nanopowders and sintered in H-2 atmosphere. The spectral properties of Ce3+:( Lu0.7Y0.25La0.05)(2)O-3 transparent ceramics were investigated and the luminescence of Ce3+ in the solid solution of Lu2O3, Y2O3 and La2O3 has been found. The ceramics has high density of 8.10g/cm(3) and short fluorescence lifetimes of 7.15 ns and 26.92 ns. It is expected to be a good fast response high temperature inorganic scintillating materials. (C) 2008 Optical Society of America.

Influence of carbon on the thermoluminescence and optically stimulated luminescence of α -Al2O3:C crystals

alpha-Al2O3:C crystal shows excellent thermoluminescence (TL) and optically stimulated luminescence (OSL) properties but the real role carbon plays in this crystal is still not clearly understood so far. In this work, alpha-Al2O3:C crystal doping with different amounts of carbon were grown by the temperature gradient technique, and TL and OSL properties of as-grown crystals were investigated. Additionally, a mechanism was proposed to explain the role of carbon in forming the TL and OSL properties of alpha-Al2O3:C. TL and OSL intensities of as-grown crystals increase with the increasing amount of carbon doping in the crystal, but no shift is found in the glow peak location at 465 K. As the amount of carbon doping in the crystals decreases, OSL decay rate becomes faster. With the increase in heating rate, the integral TL response of as-grown crystals decreases and glow peak shifts to higher temperatures. TL response decrease rate increases with the increasing amount of carbon doping in the crystals. All the TL and OSL response curves of as-grown crystals show linear-sublinear-saturation characteristic, and OSL dose response exhibits higher sensitivity and wider linear dose range than that of TL. The crystal doping with 5000 ppm carbon shows the best dosimetric properties. Carbon plays the role of a dopant in alpha-Al2O3:C crystal and four-valent carbon anions replace the two-valent anions of oxygen during the crystal growth process, and large amounts of oxygen vacancies were formed, which corresponds to the high absorption coefficient of F and F+ centers in the crystals.

Continuous-wave and Q-switched operation of a resonantly pumped Ho:YAlO3 laser

We demonstrated continuous-wave ( CW) and Q-switched operation of a room-temperature Ho: YAlO3 laser that is resonantly end-pumped by a diode-pumped Tm: YLF laser at 1.91 mu m. The CW Ho: YAlO3 laser generated 5.5 W of linearly polarized (E parallel to c) output at 2118 nm with beam quality factor of M-2 approximate to 1.1 for an incident pump power of 13.8 W, corresponding to optical-to-optical conversion efficiency of 40%. Up to 1-mJ energy per pulse at pulse repetition frequency (PRF) of 5 kHz, and the maximum average power of 5.3-W with FWHM pulse duration of 30.5 ns at 20 kHz were achieved in Q-switched mode. (C) 2008 Optical Society of America.

Growth of alpha-Al2O3:C crystal with highly sensitive optically stimulated luminescence

In this work. an alpha-Al2O3:C crystal was directly grown by the temperature gradient technique (TGT) using Al2O3 and graphite powders as the raw materials. The optical, optically stimulated luminescence (OSL) properties and dosimetric characteristics of as-grown crystal were investigated. As-grown alpha-Al2O3:C crystal shows strong absorption band at 205, 230 and 256 nm. Three-dimensional thermoluminescence (TL) emission spectrum of the crystal shows a single emission peak at similar to 415 nm. The OSL decay curve can be fitted to two exponentials, the faster component and the slower component. The OSL response of the crystal shows a linear-sublinear-saturation characteristic. As-grown alpha-Al2O3:C crystal shows excellent linearity in the dose range from 5 x 10(-6) to 50 Gy. For doses higher than the saturation dose (100 Gy). the OSL sensitivity decreases as the dose increases. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.