Effects of gamma-irradiation and air annealing on Yb-doped Y<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> single crystal

The effects of gamma-irradiation on the air-annealed 10 at.% Yb:Y3Al5O12 (YAG) and air annealing on the gamma-irradiated 10at.% Yb:YAG have been studied by the difference absorption spectra before and after treatment. The gamma-irradiation and air annealing led to opposite changes of the absorption properties of the Yb:YAG crystal. After air annealing, the gamma-irradiation induced centers were totally removed and the concentration of Fe3+ and Yb3+ were lightly increased. For the first time, the gamma-irradiation induced valence changes between Yb3+ and Yb2+ ions in Yb:YAG crystals have been observed. (C) 2007 Elsevier B.V. All rights reserved.

Growth and spectral properties of Er:Gd<inf>2</inf>SiO<inf>5</inf> crystal

Er3+ -doped Gd2SiO5 (Er:GSO) single crystal with dimensions of circle divide 35 x 40 mm(3) has been grown by the Czochralski method. The absorption and fluorescence spectra of the Er:GSO crystal were measured at room temperature. The spectral parameters were calculated based on Judd-Ofelt theory, and the intensity parameters Omega(2), Omega(4) and Omega 6 are obtained to be 6.168 x 10(-20), 1.878 x 10(-20), and 1.255 x 10(-20) cm(2), respectively. The emission cross-section has been calculated by Fuechtbauer-Ladenbury formula. (c) 2007 Elsevier B.V. All rights reserved.

Growth and spectral properties of Yb,Tm:YAG crystal

The YAG crystal codoped with Yb3+ and Tm3+ has been grown by Czochralski (Cz) method. The crystal structure of the crystal has been determined by X-ray diffraction analysis. The absorption and emission spectra of Yb,Tm:YAG crystal at room temperature have also been studied. The emission cross-sections have been calculated by Fuechtbauer-Ladenburg formula and reciprocity method. (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 &alpha; -Al<inf>2</inf>O<inf>3</inf>: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.

Bulk crystal growth and efficient diode-pumped laser performance of Yb ³⁺:Sc<inf>2</inf>SiO<inf>5</inf>

A bulk crystal of Yb:Sc2SiO5 (Yb:SSO) with favorable thermal properties was successfully obtained by the Czochralski method. The energy level diagrams for Yb:SSO crystal were determined by optical spectroscopic analysis and semi-empirical crystal-field calculations using the simple overlap model. The full width at half maximum of the absorption band centering at 976 nm was calculated to be 24 nm with a peak absorption cross-section of 9.2x10(-21) cm(2). The largest ground-state splitting of Yb3+ ions is up to 1027 cm(-1) in a SSO crystal host. Efficient diode-pumped laser performance of Yb:SSO was primarily demonstrated with a slope efficiency of 45% and output power of 3.55 W.

Yb:Y2O2S������������������������������

���������������������������������������5%Yb���������������������(Y2O2S)������������������������������������������������������������������������Yb3+���������Y2O2S���������������������������������������������������Yb3+���������2F7/2���������Y2O2S������������������709cm-1������������Yb3+������������������������������������������5���Yb���Y2O2S���������������������������������������������������������������������������������5���Yb���YAG������������������������

Continuous-wave and passively mode-locked Yb : GYSO lasers pumped by diode lasers

We report both continuous-wave and passively mode-locked laser actions in a Yb3+-doped gadolinium yttrium oxyorthosilicate Yb:GdySiO(5) (Yb:GYSO) crystal. Continuous-wave (CW) laser operations were compared under different pump conditions with high-power diodes of different wavelengths and fiber cores. CW mode-locking was obtained with a semiconductor saturable absorber mirror.

Generation of 210 fs laser pulses at 1093 nm by a self-starting mode-locked Yb:GYSO laser

We report the first demonstration, to our knowledge, of the femtosecond laser operation by using a new alloyed Yb:GYSO crystal as the gain medium. With a 5 at. % Yb3+-doped sample and chirped mirrors for dispersion compensation, we obtained pulses as short as 210 fs at the center wavelength of 1093 nm. The average mode-locking power is 300 mW, and the pulse repetition frequency is 80 MHz. (C) 2008 Optical Society of America

Luminescence behavior of Yb(3+)heavy-doped yttrium lanthanum oxide transparent ceramics

Yb3+ heavy-doped yttrium lanthanum oxide transparent ceramics were fabricated and their spectroscopic properties were investigated. The absorption bands of (YbxY0.9-xLa0.1)(2)O-3 (x = 0.05-0.15) ceramics are broad at wavelength of 900-1000 nm. The absorption cross-sections centered at 974 nm and the emission cross-sections at 1031 nm of Yb3+ ion are 0.89-1.12 x 10(-20) cm(2) and 1.05 x 10(-20) cm(2) respectively. The up-conversion luminescence intensity of Yb3+-doped yttrium lanthanum oxide ceramics increased firstly, then decreased with the increase of Yb3+ ion content. (C) 2008 Elsevier B.V. All rights reserved.

Study of thin-film SO2 gas sensors by photometric and ellipsometric methods

Pt-, Pd-, and Zr-doped SnO2 thin films and dopant-free VOx films were fabricated by planar magnetron sputtering. Tests for sensitivity to SO2 for all samples were conducted at 180 degreesC, and the sensitivities were investigated ex situ with photometric and ellipsometric methods at room temperature. It was found that the optical sensitivities as well as the sensitive wavelength region for SnO2 films could be tuned by doping. The Pd-doped SnO2 films had good sensitivity in the visible range, and the Zr-doped in the near IR. The dominant sensitive wavelength region for VOx films fell into the visible range, and the ratio of the sensitivity in the visible to that in the near IR increased with O-2/Ar in the depositing atmosphere. (C) 2001 society of Photo-Optical instrumentation Engineers .

Propriedades ��pticas do Mn2+ em sistemas Mg-Si-O

O objetivo deste trabalho foi investigar amostras do tipo MgSiO dopadas com 1,0% e 5,0% de Mn2+, obtidas em temperatura ambiente que luminesceram na faixa do vermelho. As amostras foram produzidas por rea����o de estado s��lido sob alta temperatura e caracterizadas e pelo m��todo de difra����o de raios X. Para an��lise das caracter��sticas f��sicas presentes na amostra ap��s a dopagem, usamos a espectroscopia de fotoluminesc��ncia. Atrav��s da teoria do campo cristalino, dos espectros de luminesc��ncia e excita����o e com a ajuda do diagrama e das matrizes de Tanabe-Sugano, foi poss��vel identificar as luminesc��ncias, os n��veis de energia excitados, os par��metros de energia do campo cristalino, os par��metros de Racah e a simetria do s��tio ocupado por Mn2+.

Identifica����o da forma����o de titanato de b��rio a partir de mistura reacional calcinada em diferentes temperaturas via difra����o de raios X, espectroscopia fotoac��stica e an��lise t��rmica

Os materiais ferroel��tricos t��m sido utilizados em muitas ��reas da tecnologia e da ci��ncia, pois possuem um grande n��mero de aplica����es, como: sensores; transdutores; capacitores; dispositivos ��pticos; dentre outras. A busca por novos materiais cer��micos ferroel��tricos tem sido grande. Um dos materiais cer��micos ferroel��tricos mais estudados �� o titanato de b��rio (BT). S��o v��rios os m��todos de produ����o e caracteriza����o do titanato de b��rio. Neste trabalho, p��s cer��micos de titanato de b��rio foram obtidos por rea����o do estado s��lido a partir de misturas reacionais calcinadas em diferentes temperaturas entre 400C e 900C. Foram tr��s as misturas reacionais: n��o dopadas; dopadas com 1%; e dopadas com 5% de di��xido de c��rio (CeO2). A identifica����o da forma����o do BT, nos p��s cer��micos produzidos, foi feita a partir de tr��s t��cnicas de caracteriza����o: difra����o de raios X (DRX); espectroscopia fotoac��stica (PAS); e t��cnicas de an��lise t��rmica. Com a t��cnica DRX, difratogramas mostraram que a plena forma����o do titanato de b��rio ocorreu a partir da temperatura de calcina����o de 700C. Para a amostra n��o dopada com c��rio e calcinada a 800C, houve deslocamento de todos os picos de difra����o. Nas amostras dopadas com di��xido de c��rio houve deslocamento de todos os picos de difra����o, em rela����o as amostras n��o dopadas. Observou-se tamb��m que nas amostras dopadas com 5% de CeO2, e calcinadas a 700C e 800C, res��duos de di��xido de c��rio foram observados nos difratogramas. Com a t��cnica PAS, espectros de absor����o foram obtidos. Foi poss��vel observar uma grande diferen��a de absor����o da amostra calcinada a 600 e 630C, indicando a forma����o do titanato de b��rio a partir da temperatura de 630&#61616;C, nas amostras sem a dopagem di��xido de c��rio. Houve um alargamento nas bandas de absor����o a partir da temperatura de 600C, quando o di��xido de c��rio entrou na matriz. Foi tamb��m poss��vel determinar as energias de band-gap das amostras utilizando o m��todo de Tauc. Com as t��cnicas de an��lise t��rmica, em especial atrav��s da t��cnica termogravim��trica (TG/DTG), foi comprovado que at�� 400C n��o havia forma����o de titanato de b��rio. Visto que nesta temperatura de calcina����o houve a maior perda de massa durante a rampa de aquecimento. O in��cio da forma����o do titanato de b��rio foi observado a partir da temperatura de calcina����o de 500C, assim como nas t��cnicas DRX e PAS. Portanto, com os resultados apresentados, foi demonstrada a identifica����o da forma����o do titanato de b��rio nas misturas reacionais calcinadas, com aux��lio das potencialidades das tr��s t��cnicas utilizadas.

S��nteses e caracteriza����es de TiO2 puro, dopado e co-dopado pelo m��todo sol-gel e suas atividades fotocatal��ticas

Nanopart��culas de di��xido de tit��nio v��m sendo extensamente empregadas como fotocatalisa-dores, j�� que s��o eficientes na degrada����o de diversos poluentes. Visando a obten����o de tit��-nias com diferentes propriedades, realizaram-se s��nteses atrav��s do m��todo sol-gel, a partir da hidr��lise do tetraisoprop��xido de tit��nio (IV) TIPP e seguindo-se os princ��pios da Qu��mica Verde, dispensando-se temperaturas e press��es elevadas. Foi estudada a influ��ncia de dife-rentes par��metros, como: pH, solvente, raz��o molar ��lcool/TIPP e ordem de adi����o dos rea-gentes. Foram obtidas tit��nias na forma cristalina anat��sio, nanom��tricas, com elevadas ��reas superficiais espec��ficas e predominantemente mesoporosas. Visando-se obter tit��nias com melhores propriedades ��ticas, isto ��, capazes de sofrer a fotoativa����o pela luz vis��vel, foram sintetizadas tit��nias dopadas e co-dopadas com os metais ferro e rut��nio (Fe3+ e Ru3+) e o a-metal N (N3). A s��ntese desses materiais tamb��m foi realizada atrav��s do m��todo sol-gel, sendo a dopagem realizada durante o processo de hidr��lise. As amostras foram caracterizadas na forma de p�� por difra����o de raios-X, adsor����o-dessor����o de nitrog��nio, microscopia ele-tr��nica de varredura e espectroscopia de reflet��ncia difusa no UV-Vis��vel. A tit��nia pura a-presentou como ��nica fase cristalina o anat��sio, quando calcinada at�� 400 C, com a presen��a de tra��os de brookita. A partir de 600 C, observou-se o aparecimento da fase rutilo, que em 900C foi a ��nica fase encontrada na tit��nia. A dopagem com Ru3+dificultou a transforma����o de fase anat��sio para rutilo, ao contr��rio da dopagem com Fe3+. O processo de co-dopagem acelerou a forma����o de rutilo, que se apresentou como ��nica fase nas amostras calcinadas a 600 C. As tit��nias dopadas apresentaram uma leve diminui����o na energia de bandgap, sendo os dopantes capazes de deslocar a absor����o para o vermelho. Foram realizados testes fotoca-tal��ticos visando �� degrada����o do azocorante Reactive Yellow 145 com l��mpada de vapor de merc��rio de 125 W a fim de se comparar as atividades fotocatal��ticas das tit��nias puras, dopa-das e co-dopadas, calcinadas a 300C. De todas as tit��nias sintetizadas, a tit��nia pura foi a que melhor degradou o corante, tendo um desempenho semelhante ao do TiO2 P25, da Evo-nik