Pump-probe technique for excited state absorption and stimulated emission measurements in rare earth ion doped solid materials

Rare earth ion doped solid state materials are the most important active media of near-infrared and visible lasers and other photonic devices. In these ions, the occurrence of Excited State Absorptions (ESA), from long lived electronic levels, is commonplace. Since ESA can deeply affect the efficiencies of the rare earth emissions, evaluation of these transitions cross sections is of greatest importance in predicting the potential applications of a given material. In this paper a detailed description of the pump-probe technique for ESA measurements is presented, with a review of several examples of applications in Nd3+, Tm3+ and Er3+ doped materials

Spectroscopic characterization of possible Nd3+ and Tm3+ laser active media

Este trabalho vem a dar uma importante contribuição à pesquisa de novos materiais que possam ser utilizados como meios ativos para lasers de estado sólido na região do infravermelho próximo, bombeados por lasers de diodo, e também na região do visível, bombeados pelo processo de Upconversion. As emissões dos íons Nd3+ e Tm3+ foram estudadas em três sistemas (cristalino, vítreo e policristalino). No primeiro sistema inclui-se fibras monocristalinas com diâmetro de 500 µm e até 3 cm de comprimento dos vanadatos YVO4, Y0,8La0,2VO4 e Gd0,8La0,2VO4, dopadas com Nd3+, e de Gd0,8La0,2VO4 dopadas com Tm3+, que foram crescidas pela versátil técnica LHPG, de baixo custo, e caracterizadas dos pontos de vista estrutural e espectroscópico como candidatas para o desenvolvimento de lasers compactos na região do IV e do VIS. Foi observada emissão laser em 1,064µ, foi observada em uma fibra de YVO4:Nd3+ adaptada a uma cavidade end-pump, com eficiência comparável a de um cristal comercial crescido pelo método de Czochralski. Para os vidros calcogenetos GaLaS dopados com Nd3+ e Tm3+, além das caracterizações espectroscópicas, realizou-se o estudo da transferência de energia entre íons, das interações íon-matriz e da geração de calor nas amostras, para investigar a influência destes mecânicas na eficiência quântica de emissão dos íons. Para o GaLaS:Tm3+, verificou-se ganho óptico positivo em 1,8 µm (emissão de interesse em medicina e odontologia), e medidas de absorção de estado excitado indicam que a transição em 1,4 µm pode ser utilizada em amplificadores de banda larga, desde que seja bombeada apropriadamente. As amostras da cerâmica ferroelétrica PLZT(9/65/35) transparentes e dopadas com ambos os íons foram caracterizadas de maneira similar aos outros sistemas e cálculo das propriedades radiativas aliadas as medidas do espectro de ganho no PLZT:Nd3+ indicam a potencialidade dessas matrizes como meio ativo para lasers.In this work we have made an important contribution to the growing research of new laser materials that can be pumped by low cost diode lasers or by the Upconversion process to operate in the near-infrared and visible spectral regions. Three kinds of hosts, doped with the rare earth ions (Nd3+ and Tm3+) were studied, and they present potential characteristics as laser active media. Single crystal fibers of yttrium and gadolinium orthovanadates grown by LHPG are very attractive for the construction of compact lasers due to the versatility and low cost of the growing process. A neodymium-doped YVO4 fiber adapted to an end-pump laser cavity presented efficient emission at 1.064 µm, similar to that obtained for a Czochralski grown bulk crystal. A study of ion-ion and host-ion interactions was done for GaLaS glass to investigate the influence of these processes on fluorescence quantum efficiencies. For GaLaS:Tm3+, positive gain was estimated at 1,8 µm and it was also observed that the 1,47 µm emission is efficient under appropriate pumping. Finally, transparent PLZT ferroelectric ceramic samples were characterized and the results also point out that PLZT:Nd3+ might become a potential laser host

Spectroscopic characterization of possible Nd3+ and Tm3+ laser active media

Este trabalho vem a dar uma importante contribuição à pesquisa de novos materiais que possam ser utilizados como meios ativos para lasers de estado sólido na região do infravermelho próximo, bombeados por lasers de diodo, e também na região do visível, bombeados pelo processo de Upconversion. As emissões dos íons Nd3+ e Tm3+ foram estudadas em três sistemas (cristalino, vítreo e policristalino). No primeiro sistema inclui-se fibras monocristalinas com diâmetro de 500 µm e até 3 cm de comprimento dos vanadatos YVO4, Y0,8La0,2VO4 e Gd0,8La0,2VO4, dopadas com Nd3+, e de Gd0,8La0,2VO4 dopadas com Tm3+, que foram crescidas pela versátil técnica LHPG, de baixo custo, e caracterizadas dos pontos de vista estrutural e espectroscópico como candidatas para o desenvolvimento de lasers compactos na região do IV e do VIS. Foi observada emissão laser em 1,064µ, foi observada em uma fibra de YVO4:Nd3+ adaptada a uma cavidade end-pump, com eficiência comparável a de um cristal comercial crescido pelo método de Czochralski. Para os vidros calcogenetos GaLaS dopados com Nd3+ e Tm3+, além das caracterizações espectroscópicas, realizou-se o estudo da transferência de energia entre íons, das interações íon-matriz e da geração de calor nas amostras, para investigar a influência destes mecânicas na eficiência quântica de emissão dos íons. Para o GaLaS:Tm3+, verificou-se ganho óptico positivo em 1,8 µm (emissão de interesse em medicina e odontologia), e medidas de absorção de estado excitado indicam que a transição em 1,4 µm pode ser utilizada em amplificadores de banda larga, desde que seja bombeada apropriadamente. As amostras da cerâmica ferroelétrica PLZT(9/65/35) transparentes e dopadas com ambos os íons foram caracterizadas de maneira similar aos outros sistemas e cálculo das propriedades radiativas aliadas as medidas do espectro de ganho no PLZT:Nd3+ indicam a potencialidade dessas matrizes como meio ativo para lasers.In this work we have made an important contribution to the growing research of new laser materials that can be pumped by low cost diode lasers or by the Upconversion process to operate in the near-infrared and visible spectral regions. Three kinds of hosts, doped with the rare earth ions (Nd3+ and Tm3+) were studied, and they present potential characteristics as laser active media. Single crystal fibers of yttrium and gadolinium orthovanadates grown by LHPG are very attractive for the construction of compact lasers due to the versatility and low cost of the growing process. A neodymium-doped YVO4 fiber adapted to an end-pump laser cavity presented efficient emission at 1.064 µm, similar to that obtained for a Czochralski grown bulk crystal. A study of ion-ion and host-ion interactions was done for GaLaS glass to investigate the influence of these processes on fluorescence quantum efficiencies. For GaLaS:Tm3+, positive gain was estimated at 1,8 µm and it was also observed that the 1,47 µm emission is efficient under appropriate pumping. Finally, transparent PLZT ferroelectric ceramic samples were characterized and the results also point out that PLZT:Nd3+ might become a potential laser host

Glass-to-Vitroceramic Transition in the Yttrium Aluminoborate System: Structural Studies by Solid-State NMR

The crystallization of laser glasses in the system (B(2)O(3))(0.6){(Al(2)O(3))(0.4-y)(Y(2)O(3))(y)} (0.1 <= y <= 0.25) doped with different levels of ytterbium oxide has been investigated by X-ray powder diffraction, differential thermal analysis, and various solid-state NMR techniques. The homogeneous glasses undergo major phase segregation processes resulting in crystalline YBO(3), crystalline YAI(3)(BO(3))(4), and residual glassy B(2)O(3) as the major products. This process can be analyzed in a quantitative fashion by solid-state (11)B, (27)Al, and (89)Y NMR spectroscopies as well as (11)B{(27)Al} rotational echo double resonance (REDOR) experiments. The Yb dopants end up in both of the crystalline components, producing increased line widths of the corresponding (11)B, (27)Al, and (89)Y NMR resonances that depend linearly on the Yb/Y substitution ratio. A preliminary analysis of the composition dependence suggests that the Yb(3+) dopant is not perfectly equipartitioned between both crystalline phases, suggesting a moderate preference of Yb to substitute in the crystalline YBO(3) component.Deutsche Forschungsgemeinschaf (DFG)Deutsche Forschungsgemeinschaft (DFG)FAPESP[04/00093-0]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CAPES[455/04-1]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPqAlexander-von-Humboldt FoundationAlexander von Humboldt Foundation (AvH)NRW ForschungsschuleNRW Forschungsschul

Preparation and structural characterization of rare-earth doped lead lanthanum zirconate titanate ceramics

A new preparation route towards rare-earth (RE) doped polycrystalline lead lanthanum zirconate titanate (PLZT) ceramics (RE = Y(3+), Nd(3+), Yb(3+)), based on the use of doped lanthanum oxide or zirconia, is reported. Structural characterization by X-ray powder diffraction reveals that secondary phase formation can be substantially diminished in comparison to conventional preparation methods. The distribution of the rare-earth dopants was investigated as a function of concentration by static (207)Pb spin echo NMR spectra, using Fourier Transformation of Carr-Purcell-Meiboom-Gill spin echo trains. For the Nd- and Yb-doped materials, the interaction of the (207)Pb nuclei with the unpaired electron spin density results in significant broadening and shifting of the NMR signal, whereas these effects are absent in the diamagnetic Y(3+) doped materials. Based on different concentration dependences of the NMR lineshape parameters, we conclude that the structural role of the Nd(3+) dopants differs significantly from that of Yb(3+). While the Nd(3+) ions appear to be statistically distributed in the PLZT lattice, incorporation of Yb(3+) into PLZT appears to be limited by the appearance of doped cubic zirconia as a secondary phase. (C) 2009 Elsevier Masson SAS. All rights reserved.Alexander von Humboldt Foundation (AvH)Alexander von Humboldt-Foundatio

Structural models for yttrium aluminium borate laser glasses: NMR and EPR studies of the system (Y(2)O(3))(0.2)-(Al(2)O(3))(x)-(B(2)O(3))(0.8-x)

The structure of laser glasses in the system (Y(2)O(3))(0.2){(Al(2)O(3))(x))(B(2)O(3))(0.8-x)} (0.15 <= x <= 0.40) has been investigated by means of (11)B, (27)Al, and (89)Y solid state NMR as well as electron spin echo envelope modulation (ESEEM) of Yb-doped samples. The latter technique has been applied for the first time to an aluminoborate glass system. (11)B magic-angle spinning (MAS)-NMR spectra reveal that, while the majority of the boron atoms are three-coordinated over the entire composition region, the fraction of three-coordinated boron atoms increases significantly with increasing x. Charge balance considerations as well as (11)B NMR lineshape analyses suggest that the dominant borate species are predominantly singly charged metaborate (BO(2/2)O(-)), doubly charged pyroborate (BO(1/2)(O(-))(2)), and (at x = 0.40) triply charged orthoborate groups. As x increases along this series, the average anionic charge per trigonal borate group increases from 1.38 to 2.91. (27)Al MAS-NMR spectra show that the alumina species are present in the coordination states four, five and six, and the fraction of four-coordinated Al increases markedly with increasing x. All of the Al coordination states are in intimate contact with both the three-and the four-coordinate boron species and vice versa, as indicated by (11)B/(27)Al rotational echo double resonance (REDOR) data. These results are consistent with the formation of a homogeneous, non-segregated glass structure. (89)Y solid state NMR spectra show a significant chemical shift trend, reflecting that the second coordination sphere becomes increasingly ""aluminate-like'' with increasing x. This conclusion is supported by electron spin echo envelope modulation (ESEEM) data of Yb-doped glasses, which indicate that both borate and aluminate species participate in the medium range structure of the rare-earth ions, consistent with a random spatial distribution of the glass components.NRW Graduate School of ChemistryAlexander von Humboldt Foundation (Germany

Luminescence characteristics of YAP:Ce scintillator powders and composites

Cerium doped yttrium aluminate perovskite YAlO(3) (YAP) powders are pursued as interesting alternatives to bulk crystals for application in scintillating devices. The emissions of these materials in the near-UV and visible spectral regions originate from electric dipole transitions between 4f and 5d energy levels of Ce(3+) and largely depend on the environment occupied by the ion. In search for improved synthesis conditions that can lead to phase pure powders with optimized structural and spectroscopic characteristics, in this work we have employed the polymeric precursor (Pechini) method to prepare crystalline and amorphous YAP:Ce powders doped with 1-10 mol% Ce(3+). Interesting composite materials were also obtained by dispersing some of the YAP:Ce powders in silica xerogels. A comparative structural and spectroscopic study of all the samples was done by XRD, FT-IR, emission, excitation and excited state lifetime measurements. In agreement with previous reports, excitation at 296 nm results in intense emission in the range 315-425 nm with an average decay time of 30 ns. (c) 2010 Elsevier B.V. All rights reserved.FAPESP (Brazil)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPq (Brazil)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)DFG (Germany)Deutsche Forschungsgemeinschaf (DFG)Alexander von Humboldt Foundation (AvH)Alexander von Humboldt Foundatio

Energy transfer processes in Yb(3+)-Tm(3+) co-doped sodium alumino-phosphate glasses with improved 1.8 mu m emission

Sodium alumino-phosphate glasses co-doped with Yb(3+) and Tm(3+) ions have been prepared with notably low OH(-) content, and characterized from the viewpoint of their spectroscopic properties. In these glasses, Yb(3+) acts as an efficient sensitizer of excitation energy at 0.98 mu m - which can be provided by high power and low cost diode lasers, and subsequently undergoes non-resonant energy transfer to Tm(3+) ions ((2)F(5/2), (3)H(6) --> (2)F(7/2), (3)H(5)). Through this process, the emitting level (3)F(4) is rapidly populated, generating improved emission at 1.8 mu m ((3)F(4) --> (3)H(6)). In order to guarantee the efficiency of such favorable energy transfer, energy losses via multiphonon decay, Yb-Yb radiative trapping, and non- radiative transfer to OH(-) groups were evaluated, and minimized when possible. The dipole - dipole energy transfer microscopic parameters corresponding to Yb(3+) --> Tm(3+), Yb(3+) --> Yb(3+) and Tm(3+) --> Tm(3+) transfers, calculated by the Forster-Dexter model, are C(Yb-Tm) = 2.9 x 10(-40) cm(6) s(-1), C(Yb-Yb) = 42 x 10(-40) cm(6) s(-1) and C(Tm-Tm) = 43 x 10(-40) cm(6) s(-1), respectively

Cooperative upconversion, radiation trapping end self-quenching effects in highly Yb3+ - doped oxyfluoride glasses

In this work we report the successful preparation of fluorophosphate glasses in the new compositional line 20Al(PO3)3-10AlF3-25BaF2-25SrF2-(20 - x)YF3-xYbF3 with x varying from 0 to 20 mol%, and their detailed spectroscopic investigation with respect to (non-) radiative decay processes. More precisely, we focus on the study of three important effects in Yb3+ doped systems, namely radiation trapping (RT), self quenching (SQ), and cooperative luminescence (CL). The characteristic improvement in hydrolytic stability and phonon energy of the glasses, as compared to phosphates, for example, result in long 2F5/2 radiative lifetime value (π0 = 1.2 ms) and high critical Yb3+ concentration (Q = 6.8 × '10 POT. 20' ions/cm3). A very strong radiation trapping effect was observed in the investigated samples which can be favorably used to generate highly efficient energy upconversion in the blue, through Yb–Yb cooperative effect. The CL was investigated and quantified yielding, to the best of our knowledge, the highest CL parameter [k = (5.85 ± 0.08) × '10 POT. -18' cm3/s], which is associated to a CL rate of 32 s–1 for a typical pump power of ∼100 mW. These characteristics evidence the potential applications of the present YbM3+-doped oxyfluoride glasses for blue emitting devices, as well as for infrared ones

Spectroscopic features of erbium-doped CaM2O6 (M = Nb, Ta) single crystal fibers grown by the laser-heated pedestal growth technique

Erbium-doped single crystal fibers, with low phonon energy and fairly high absorption and emission cross sections are interesting laser active media, for compact, near-infrared and/or upconversion lasers. In this work, high optical quality Er3+-doped CaNb2O6 and CaTa2O6 single crystal fibers were successfully grown by the versatile laser-heated pedestal growth technique, and characterized from the structural and spectroscopic points of view. The results indicate that these crystal fiber compositions, which had not been explored so far, offer potential applications, not only as laser active media, but also in other optical devices. (c) 2007 Elsevier B.V. All rights reserved