Cooperative up-conversion luminescence of ytterbium doped yttrium lanthanum oxide transparent ceramic

The up-conversion luminescence of Yb3+-doped yttriurn lanthanum oxide transparent ceramic was investigated. It was ascribed to cooperative luminescence originated from the coupled states of the Yb3+ ion pairs. The proper doping of La2O3 can remove the cooperative luminescence of Yb3+ ion. But excessive La2O3 (at least 10 at.%) the cooperative up-conversion of Yb3+:Y2O3 is obtained again, and the intensity of up-conversion luminescence strengthens with the increase of La2O3 content. (c) 2007 Elsevier B.V. All rights reserved.

Edge-defined, film-fed growth (EFG) technique for the preparation of alpha-Al2O3 : C crystal with highly sensitive thermoluminescence response

In this work, alpha-Al2O3:C, a highly sensitive thermoluminescence dosimetry crystal, was grown by the EFG method in which a graphite heating unit and shield acted as the carbon source during the growth process. The optical, luminescent properties and dosimetric characteristics of the crystal were investigated. The as-grown crystal shows a single glow peak at 536 K, which is associated with Cr3+ ions. After annealing in H-2 at 1673 K for 80 h, the crystal shows a single glow peak at 460 K and a blue emission band at 415 nm. The thermoluminescent response of the annealed crystal shows linear-sublinear-saturation characteristics in the dose range from 5 x 10(-6) to 100 Gy.

Fabrication and spectral properties of Nd3+-doped yttrium lanthanum oxide transparent ceramics

Transparent 1 at% Nd3+:Y1.9La0.1O3 ceramics were fabricated with nanopowders prepared by carbonate coprecipitation method. The powder compacts were sintered in H-2 atmosphere at 1550 degrees C for 30 h. The Nd3+:Y1.9La0.1O3 ceramics display uniform grains of about 50 mu m and high transparency. The highest transmittance of the ceramics reaches 67%. The strongest absorption peak is in the wavelength of 820 nm with absorption cross section of 2.48 x 10(-20) cm(2). The absorption is still high at LD wavelength 806 nm with absorption cross section of 1.78 x 10(-20) cm(2) and broad full width at half maximum (FWHM) of about 6.3 nm. The strongest emission peak was centered at 1078 nm with large stimulated emission cross section of 9.63 x 10(-20) cm(2) and broad FWHM of about 7.8 nm. The broad absorption and emission bandwidth of Nd3+:y(1.9)La(0.1)O(3) transparent ceramics are favorable to achieve the miniaturized LD pumping apparatus and ultrashort modelocked pulse laser output, respectively. (c) 2007 Elsevier B.V. All rights reserved.

Growth of highly sensitive thermoluminescent crystal alpha-Al2O3 : C by the temperature gradient technique

In this work, an alpha-Al2O3:C crystal with highly sensitive thermoluminescence was directly grown by the temperature gradient technique (TGT) using Al2O3 and graphite powders as raw materials. The optical and luminescent properties and the dosimetric characteristics of the crystal were investigated. An as-grown alpha-Al2O3:C crystal shows a single glow peak at 462 K and a blue emission peak at 415 nm. The thermoluminescence (TL) response of the crystal shows a linear-sublinear-saturation characteristic. In the dose range from 5 x 10(-6) to 10Gy, the alpha-Al2O3:C crystal shows excellent linearity, and saturation was observed at about 30Gy. The sensitivity of the crystal decreases as the heating rate increases. (c) 2008 Elsevier B.V. All rights reserved.

Influence of carbon on the thermoluminescence and optically stimulated luminescence of α -Alnf>2nf>Onf>3nf>: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.

Luminescence characteristics of Yb3+, La3+ codoped yttrium oxide nanopowders

Luminescence characteristics of Yb3+, La3+ codoped yttrium oxide nanopowders were investigated. The grain size and the crystallinity of (Yb0.05Y0.90La0.05)(2)O-3 nanopowders increase with the increase of calcination temperature. The average grain size of the nanopowders calcined at 1100 degrees C is 66 nm and its cooperative up-conversion luminescence centered at 498 nm was detected due to nanometer size effect and perfect crystallinity. However, the cooperative up-conversion luminescence of (Yb0.05Y0.90La0.05)(2)O-3 transparent ceramics was not detected. (c) 2008 Elsevier B.V. All rights reserved.