Semiconductor optoelectronics

Optical absorption, fluorescence and lifetime characteristics of Sm 3+ -doped fluoride containing phosphate glasses (PKFBASm) with molar composition of (56Àx/2) P 2 O 5 + 14 K 2 O + 6KF + (15Àx/2) BaO + 9Al 2 O 3 + x Sm 2 O 3 , (x = 0.01, 0.05, 0.1, 1.0, 2.0, 4.0 and 6.0 mol%) were studied. From the measured energies of absorption bands, different free-ion energy level parameters along with calculated energies were determined using the free-ion Hamiltonian (H FI ) model. Judd-Ofelt (J-O) theory was applied to the experimental oscillator strengths to evaluate three phenomenological J-O intensity parameters X k (k = 2, 4 and 6). Using these J-O parameters as well as from the emission and decay measurements, various radiative parameters such as transition probabilities (A R ), radiative lifetimes (s R ), measured lifetimes (s mes ), calculated branching ratios (b R ), measured branching ratios (b mes ), effective bandwidths (Dk eff ) and stimulated emission cross-sections (r kp ) have been calculated for the excited 4 G 5/2 luminescent level. The nature of decay curves of 4 G 5/2 level for different Sm 3+ ion concentrations in all PKFBASm glasses has been analyzed using Inokuti-Hirayama (I-H) model and the lifetimes are noticed to decrease with increase of concentration. The cross-relaxation mechanism responsible for the quenching of measured lifetimes with concentration is also discussed.

Spectroscopy, 2010

Two-dimensional electronic spectroscopy is a sensitive probe of solvation dynamics. Using a pump–probe geometry with a pulse shaper [Optics Express15(2007), 16681-16689;Optics Express16(2008), 17420-17428], we present temperature dependent 2D spectra of laser dyes dissolved in glass-forming solvents. At low waiting times, the system has not yet relaxed, resulting in a spectrum that is elongated along the diagonal. At longer times, the system loses its memory of the initial excitation frequency, and the 2D spectrum rounds out. As the temperature is lowered, the time scale of this relaxation grows, and the elongation persists for longer waiting times. This can be measured in the ratio of the diagonal width to the anti-diagonal width; the behavior of this ratio is representative of the frequency–frequency correlation function [Optics Letters31(2006), 3354–3356]. Near the glass transition temperature, the relaxation behavior changes. Understanding this change is important for interpreti...

The present paper describes the optical absorption, photoluminescence and lifetime measurements of trivalent samarium doped calcium fluoroborate (CFB) glasses. From the observed energy levels, the free-ion energy level parameters for the 4f 5 electronic configuration of Sm 3þ ion have been evaluated using H FI model. The experimental oscillator strengths of absorption bands have been analyzed to determine the JuddeOfelt (JeO) parameters. From the evaluated JeO parameters and luminescence data, the radiative parameters such as A R , s R and s e values were obtained from the excited 4 G 5/2 level to different lower energy levels. The decay curves of 4 G 5/2 / 6 H 7/2 transition were analyzed by the InokutieHirayama model assuming dipoleedipole interaction between the dopant ions. The decrease of fluorescence intensities as well as measured lifetimes at higher concentrations has been explained based on energy transfer process through cross-relaxation between Sm 3þ ions.

Optical and Quantum Electronics, 2007

The paper deals with optical and electronic properties of the aluminophosphate glasses containing Fe-Mn and Fe-Cr ion pairs in different concentration. The influence of the mixed alkali ions over the electronic properties has been investigated. The optical behavior (optical transmission) of the glass samples has been studied by UV-VIS spectroscopy and the refractive index dependency on wavelength has been discussed. The transmission spectra show features specific for the doping transition ions (TM), revealing different oxidation states of iron (Fe 2+ /Fe 3+ ), manganese (Mn 2+ /Mn 3+ ) and chromium (Cr 3+ /Cr 6+ ) in the vitreous network. Mössbauer spectroscopy offers information regarding the TM oxidation states, redox processes and the iron coordination symmetry in the vitreous network. In the case of Fe-Mn doped glasses, the percentage of Fe 2+ is about 40% and a doubled iron content leads to an increasing of Fe 2+ percentage up to 53%. The replacing of lithium ions by natrium ions (mixed alkali effect) provides an increasing of the Fe 2+ percentage up to 123 524 M. Elisa et al.

Doklady Physics, 2008

Physics of the Solid State, 2001

The absorption spectra of Pr 3+ and Dy 3+ ions in three glass matrices (SiO 2-P 2 O 5-GeO 2 , Al 2 O 3-B 2 O 3-SiO 2 , and LiB 3 O 5) are thoroughly studied in the near-IR spectral range (4600-14 300 cm-1). The temperature dependences of the intensity, the width, and the location of the absorption bands observed are investigated for the first time. It is shown that the f − f transitions in the studied glasses are allowed by static odd distortions in the environment of the rare-earth ions and these distortions decrease with an increase in temperature. A comparative analysis of the absorption band parameters and their temperature behavior in different materials makes it possible to determine the differences in magnitudes, symmetries, and dispersions of the distortions in the nearest environment of rare-earth ions in different glasses.

A detailed structural investigation of a series of fluoride phosphate glasses with nominal compositions 25BaF 2-25SrF 2 −(30−x)Al(PO 3) 3 −xAlF 3 − (20−z)ScF 3 :zREF 3 with x = 25, 20, and 15, RE = Yb and Eu, and 0 ≤ z ≤ 1.0, and of a Sc-free set of glasses with compositions w[80(Ba/Sr)F 2 −20AlF 3 ]− (1−w)[80Ba(PO 3) 2 −20Al(PO 3) 3 ] (w = 25, 50, 75), doped with 0.2 mol % Yb 3+ or Eu 3+ , has been conducted. As indicated by Raman scattering and solid state NMR, the network structure is dominated by aluminum−oxygen-phosphorus linkages, which can be quantified by means of 27 Al/ 31 P NMR double resonance techniques. The ligand environment of the rare-earth ions is studied by (1) 45 Sc NMR of the diamagnetic mimic Sc 3+ , (2) pulsed X-band EPR spectroscopy of Yb 3+ spin probes, and (3) excitation and emission spectroscopy of Eu 3+ dopants. The rare-earth ions are found in a mixed environment of fluoride and phosphate ions, which changes systematically as a function of glass composition. In the Sc-containing glasses the quantitative makeup of this ligand environment has been determined by 45 Sc{ 19 F} and 45 Sc{ 31 P} rotational echo double resonance (REDOR). Comparison of the P-to F-ligand ratio with the batch composition indicates that the Sc 3+ ions show a clear preference for phosphate over fluoride ion ligation. These REDOR results were correlated with Yb 3+ EPR data, the intensity ratio of Eu 3+ transitions 5 D 0 → 7 F 2 to 5 D 0 → 7 F 1 , and the lifetime values of the Eu 3+ emitting level 5 D 0. As a result, it was possible to obtain a global interpretation in terms of the associated quantitative ligand distribution (fluoride versus phosphate) in the first coordination sphere of the rare earth ions. The calibration of EPR and luminescence spectra on the basis of such solid state NMR data defines a new spectroscopic strategy for characterizing the rare-earth local environments in promising laser glasses. ■ INTRODUCTION Rare-earth (RE) ion-doped transparent glasses and glass-ceramics are well established materials for the design of new-generation lasers and other photonic devices. 1−13 Efficient dispersal of the luminescent species can be accomplished in a variety of glass matrices 14−16 each one of which presents characteristic advantages and disadvantages from the application standpoint. 17 Fluoride phosphate glasses play an important role in this effort. Numerous promising RE-doped compositions have been developed, characterized with regard to their photophysical properties, and functionally tested. 18−25 The goal is to design a framework structure dominated by bridging oxygen links between the network formers, resulting in high mechanical stability, while, at the same time, creating a fluoride-dominated low-phonon energy local environment for the luminescent ions, which favors high fluorescence quantum efficiencies and long excited-state lifetime values. To examine the validity and feasibility of this design concept, detailed information is required on the local environments of the luminescent ions. Owing to its element-selectivity and inherently quantitative character, and because the lack of long-range order does not interfere with the spectroscopic information obtained, solid state NMR has developed into an extremely powerful structural characterization method for glasses. 26 While the method has given invaluable information on short and medium range order of the glassy framework, the experimental characterization of the local environment of fluorescent RE ions in these glasses is complicated by the 4f n-paramagnetism of these ions, which broadens their NMR signals beyond detectability. To overcome these problems, we have developed a three-pronged strategy, involving (1) NMR studies on diamagnetic trivalent ions functioning as mimics for the luminescent species, (2) pulsed EPR studies of the paramagnetic RE ions themselves, probing direct ligation and/or spatial proximity to nuclear spins in their vicinity, and (3) the measurement of optical/photophysical characteristics. Previously , we applied this strategy to a set of new fluoroalumino-phosphate glasses, with composition 25BaF 2 −25SrF 2 − (30−x)Al(PO 3) 3 −xAlF 3 −(20−z)YF 3 −zREF 3 , For each composition x two RE doped glasses were synthesized, with RE 3+ = Eu 3+ or Yb 3+ and z = 0.2 or 5.0 mol %. 27 We studied the framework by a

Journal of Non-Crystalline Solids, 1992

In this paper, we report the preparation and optical characterization of Mn 2 activated Pr 3 doped phosphate glasses in four dierent chemical compositions. The optical absorption spectra of Pr 3 ions in phosphate glasses have been recorded in the UV±VIS±NIR region. From the data available in the optical absorption spectra, various spectroscopic parameters such as Slater±Condon (F 2 , F 4 , F 6 ), Racah (E 1 , E 2 , E 3 ), spin-orbit interaction (n 4f ) and Judd±Ofelt (J±O) (X 2 , X 4 , X 6 ) parameters are derived. The calculated values of the J±O parameters are utilized in evaluating the various radiative parameters such as electric dipole line strengths (S ed ), magnetic dipole line strengths (S md ), radiative transition probabilities (A RAD ), radiative lifetimes (s RAD ),¯uorescence branching ratios (b R ) and the integrated absorption crosssections (r a ) for stimulated emission from various excited states of Pr 3 ion. The principal¯uorescence transitions of interest are identi®ed by recording the¯uorescence spectrum and measuring their stimulated emission cross-section and optical gain. Quantum eciencies of the prominent lasing transitions are estimated by measuring their radiative and uorescence lifetimes. The dependence of eective radiative lifetime on Pr 3 ion concentration is discussed in the light of non-radiative processes such as multiphonon relaxation and energy transfer between like and unlike ions. Ó

Journal of Non-Crystalline Solids, 2006

Fluoride)phosphate and borosilicate glasses of high intrinsic transparency in the deep ultraviolet (UV), were doped with 50-5000 ppm of the 4d-and 5d-ions Zr, Nb, Ta, Mo, or W. All of these ions absorb strongly in the UV. Samples plates were irradiated by UV lasers and the as a consequence generated various extrinsic and intrinsic defects were characterized by optical and EPR spectroscopy. The laser induced transmission changes depend not only on the glass matrix, but also on the valence of the dopants. Only fully oxidized d 0 -ions are observed in fluoroaluminate glasses. Laser irradiation photoreduces the d 0 -ions to extrinsic electron-centers (EC). Laser induced transmission changes extend from the UV up to 600 nm in the visible. The dopants are easily reduced to lower valences in metaphosphate glasses. Extrinsic hole centers (HC) replace intrinsic HC in samples containing the reduced transition metal ions. The strong transmission changes seen below 300 nm arise from intrinsic EC and extrinsic HC. The few remaining intrinsic HC (300-600 nm) recombine rapidly with EC or transform into more stable extrinsic HC. Borosilicate glasses show the formation of intrinsic boron oxygen hole center in the EPR spectra and of intrinsic HC and EC in the optical spectra. The d 1 -ion Mo 5+ is the only identified reduced dopant species in the borosilicate glasses. The band intensity of intrinsic EC in relation to intrinsic HC is correspondingly highest for the Mo-doped samples, in which extrinsic HC are generated.

Nd 3þ doped H 3 BO 3 -PbO-TeO 2 -RF (R ¼ Li, Na and K) glasses were prepared through melt quenching technique. Optical absorption and near infrared (NIR) fluorescence spectra were recorded at room temperature. The spectral intensities were analyzed in terms of the Judd-Ofelt (J-O) parameters (U l ¼ 2, 4, 6). The covalency effect of Nd-O bond on the J-O parameters was estimated from the relative absorbance ratio (R) between 4 I 9/2 / 4 F 7/2 and 4 I 9/2 / 4 S 3/2 transitions. The effect of Nd-O covalency on the U 4 and U 6 intensity parameters as well as on the spontaneous emission probabilities (A R ) was discussed. Lomheim and Shazer hybrid method was applied to determine the fluorescence branching ratios (b R ) of each emission transition from the 4 F 3/2 metastable level to its lower lying levels. The evaluated total radiative transition probabilities (A T ), stimulated emission cross-sections (s e ) and gain bandwidth parameters (s e  Dl P ) were compared with the earlier reports.