Optical absorption and photoluminescence properties of Er3+ doped mixed alkali borate glasses

An investigations of the optical absorption and fluorescence spectra of 0.2 mol% Er2O3 in mixed alkali borate glasses of the type 67.8B2O3 x xLi2O(32-x)Na2O, 67.8B2O3 x xLi2O(32-x)K2O and 67.8B2O3 x xNa2O(32-x)K2O (where x = 8, 12, 16, 20 and 24) are presented. The glasses were obtained by quenching melts consisting of H3BO3, Li2CO3, Na2CO3, K2CO3 and Er2O3 (950-1100 degrees C, 1.5-2 h) between two brass plates. Spectroscopic parameters like Racah (E1, E2 and E3), spin-orbit (xi(4f)) and configuration interaction (alpha) parameters are deduced as function of x. Using Judd-Ofelt theory, Judd-Ofelt intensity parameters (omega2, omega4 and omega6) are obtained. Radiative and non-radiative transition rates (A(T) and W(MPR)), radiative lifetimes (tauR), branching ratios (beta) and integrated absorption cross-sections (sigma) have been computed for certain excited states of Er3+ in these mixed alkali borate glasses. Emission spectra have been studied for all the three Er3+ doped mixed alkali borate glasses. The present paper throws light on the trends observed in the intensity parameters, radiative lifetimes, branching ratios and emission cross-sections as a function of x in these borate glasses, keeping in view the effect of mixed alkalies in borate glasses.     

Temperature dependent luminescence characteristics of Sm3+-doped silicate glass

We report here on the optical characterisation of Sm3+ (5 wt%): SiO2 + Al2O3 + Li2O + Na2O + MgO glass from the measurements of optical absorption spectra (at 300 K), total luminescence spectra (10-300 K) and fluorescence lifetimes (10-300 K) of the prominent emission transitions of the Sm3+ ions. Besides its spectral properties, physical and nonlinearity characterising property parameters have also been computed to understand the optical dispersive power of this glass. By the application of Judd-Ofelt parameters (omega(lambda)) of the measured absorption spectrum, the radiative transition probability factors (A) and stimulated emission cross-section (sigma(p)E) of the observed fluorescent levels have been analysed. Both emission intensity and measured lifetimes of the prominent luminescent transition (4G(5/2) --> 6H(7/2)) concerning Sm3+-glass has been showing a descending trend with the rise in temperature with N2-laser (337.1 nm) as the source of excitation.     

Spectroscopic characteristics of Sm3+-doped alkali fluorophosphate glasses

Optical absorption, luminescence and lifetime measurements of Sm(3+)-doped alkali fluorophosphate glasses with molar compositions of 50(NaPO(3))(6)+10TeO(2)+20AlF(3)+19RF+1Sm(2)O(3) (R=Li, Na and K) are described. The variation of optical properties with glass composition plays a dominant role in the determination of efficient laser materials. From the experimental oscillator strengths of f-f electric dipole transitions, the phenomenological Judd-Ofelt parameters have been evaluated and are used to evaluate radiative parameters such as radiative transition probabilities (A(R)), branching ratios (beta(R)), lifetimes (tau(R)) and integrated absorption cross-section (sigma(a)) for various excited levels. The predicted values of tau(R) and beta(R) from the (4)G(5/2) excited level to its lower levels are compared with the experimentally measured values. Stimulated emission cross-sections (sigma(e)) were also determined for (4)G(5/2)-->(6)H(J) (J=5/2, 7/2, 9/2 and 11/2) emission transitions. From the emission transitions of Sm(3+) in these alkali tellurofluorophosphate glasses certain potential laser transitions have been identified.     

Characterization of emission properties of Er3+ ions in TeO2-CdF2-WO3 glasses

TeO(2)-CdF(2)-WO(3) glasses with various compositions and Er(3+) concentrations were prepared by conventional melting method. Their optical properties were studied by measuring the absorption, luminescence spectra and the decay patterns at room temperature. From the optical absorption spectra the Judd-Ofelt parameters (Ω(t)), transition probabilities, branching ratios of various transitions, and radiative lifetimes were calculated. The absorption and emission cross-section spectra of the (4)I(15/2) to (4)I(13/2) transition of erbium were determined. Emission quantum efficiencies and the average critical distance R(0) which provides a measure for the strength of cross relaxation were determined.     

Thermal stability, Judd-Ofelt theory analysis and spectroscopic properties of a new Er3+/Yb3+-codoped germano-tellurite glass

The Er3+/Yb3+-codoped 70TeO2-5Li2O-10B2O3-15GeO2 glass was prepared. The thermal stability, absorption spectra, emission spectra and up-conversion spectra were measured and investigated. The Judd-Ofelt analysis based on absorption spectra was performed in order to determine the Judd-Ofelt intensity parameters Omega(t) (t = 2, 4, 6), spontaneous emission probability, radiative lifetime and branching ratios of several Er3+ transitions. It was found that this studied glass has good thermal stability, broad fluorescence full width at half maximum (FWHM), large stimulated emission cross-section and strong up-conversion emissions at about 532, 546 and 659 nm, corresponding to the 2H(11/2)-->4I(15/2), 4S(3/2)-->4I(15/2) and 4F(9/2)-->4I(15/2) transitions of Er3+, respectively under the excitation at 970 nm. The results suggest that this Er3+/Yb3+-codoped germano-tellurite glass may be a potentially useful material for developing potential amplifiers and up-conversion optical devices.     

Spectroscopic investigations of Nd(3+)-doped alkali chloroborophosphate glasses

Optical absorption spectra were studied in wavelength region 400-900 nm for the Nd(3+)-doped alkali (R = Li, Na and K) chloroborophosphate glasses at room temperature. The energy level scheme of the 4f(3) electron configuration was deduced from the observed energy level data using a parametrized Hamiltonian (H(F1)) model which includes 20 free-ion interaction parameters. Reasonable correlation was obtained between the experimental and calculated energy levels. The Judd-Ofelt model for the intensity analysis of induced electric dipole transitions has been applied to the measured oscillator strengths of the absorption bands to determine the three phenomenological intensity parameters Omega(2), Omega(4) and Omega(6) for each glass. Using these parameters, the total radiative transition rates (A(T)), non-radiative relaxation rates (W(NR)), branching ratios (beta(R)), integrated cross-sections for the stimulated emission (Sigma), excited state emission intensities (f(ESE)) and excited state absorption intensities (f(ESA)) have been theoretically calculated for certain excited Nd(3+) fluorescent levels. From the results obtained, the conclusion is made about the possibility of using these glasses as laser media.     

ZBLAN玻璃中三价铒离子 2H11/2,4S3/2辐射跃迁的量子效率

为了探讨铒离子掺杂材料的激光制冷可能性, 依据测量样品的吸收光谱, 计算了Er3 掺杂的ZBLAN玻璃材料的Judd-Ofelt参数, 得到Ω2=3.01×10-20 cm2, Ω4=1.59×10-20 cm2, Ω6=1.03×10-20 cm2, 进而获得了2H11/2, 4S3/2及其以下各能级间跃迁的跃迁几率、分支比、寿命等数据. 测量了77 K到315 K温度范围内Er3 较强的两个绿色发射2H11/2, 4S3/2→4I15/2的发射谱及荧光寿命. 讨论了2H11/2, 4S3/2这样处于热平衡中的两个能级的量子效率的计算方法, 进而计算了它们的量子效率, 并与其它材料进行了比较.     

Spectroscopic properties of Dy(3+) ions in NaF-B(2)O(3)-Al(2)O(3) glasses

This paper reports the optical properties of Dy(3+) in sodium fluoroborate glasses of the type XNaF.(89-X)B(2)O(3).10 Al(2)O(3).1Dy(2)O(3) (where X=8, 12, 16, 20 and 24). Judd-Ofelt intensity parameters (Omega(2), Omega(4), Omega(6)) are derived from the absorption spectra. The Judd-Ofelt theory has been applied to interpret the local environment of Dy(3+) ions and bond covalency of RE-O bond. These parameters have been used to calculate radiative transition probabilities (A(rad)), lifetimes (tau(R)) and branching ratios (beta(R)) for the excited level (4)F(9/2). The predicted values of tau(R) are compared with the measured values for (4)F(9/2) level for five glass compositions (Glass (A-E)). The stimulated emission cross-section sigma(lambda(P)) are also evaluated for the (4)F(9/2)-->(6)H(J) (J=11/2, 13/2, and 15/2) transitions.     

The visible absorption spectrum of OBrO, investigated by Fourier transform spectroscopy

By the utilization of a new laboratory method to synthesize OBrO employing an electric discharge, the visible absorption spectrum of gaseous OBrO has been investigated. Absorption spectra of OBrO have been recorded at 298 K, using a continuous-scan Fourier transform spectrometer at a spectral resolution of 0.8 cm(-1). A detailed vibrational and rotational analysis of the observed transitions has been carried out. The FTS measurements provide experimental evidence that the visible absorption spectrum of OBrO results from the electronic transition C(2A2)-X(2B1). Vibrational constants have been determined for the C(2A2) state (omega(1) = 648.3 +/- 1.9 cm(-1) and omega 2 = 212.8 +/- 1.2 cm(-1)) and for the X(2B1) state (omega 1 = 804.1 +/- 0.8 cm(-1) and omega 2 = 312.2 +/- 0.5 cm(-1)). The vibrational bands (1,0,0), (2,0,0), and (1,1,0) show rotational structure, whereas the other observed bands are unstructured because of strong predissociation. Rotational constants have been determined experimentally for the upper electronic state C(2A2). By modeling the band contours, predissociation lifetimes have been estimated. Further, an estimate for the absorption cross-section of OBrO has been made by assessing the bromine budget within the gas mixture, and atmospheric lifetimes of OBrO have been calculated using a photochemical model.     

Absorption and emission characteristics of Er3+ ions in alkali chloroborophosphate glasses

Alkali chloroborophosphate glasses containing 1 mol% of Er3+ ions were studied experimentally using the absorption and emission spectroscopy. The energy level scheme for the 4f11 (Er3+) electronic configuration was deduced from the observed band energies of the absorption spectra in terms of a parametrized Hamiltonian using the various free-ion spectroscopic parameters. Oscillator strengths (f) measured from the absorption spectra have been analyzed using the Judd-Ofelt theory to evaluate the three intensity parameters omegalambda (lambda = 2, 4 and 6). Reasonable agreement between the measured and calculated f values has been found. Electric and magnetic dipole transition probabilities, fluorescence branching ratios, integrated emission cross sections and radiative lifetimes were calculated for all the excited states of Er3+ ions. The non-radiative (WNR) relaxation rates from the excited levels to the next lower levels have been calculated and the relationship between the energy gap and non-radiative relaxation rate has been established. These results were used to predict the possible potential laser transitions in Er-doped alkali chloroborophosphate glasses.     

Structure-dependent optical properties of single-walled silicon nanotubes

The electron excitations of Single-Walled Silicon Nanotubes (SWSiNTs), with sp(2) and sp(3) hybridization, were studied using the localized-density-matrix (LDM) method with INDO/S parameters. Strong anisotropic characteristics of the dynamic polarizabilities were found for all the nanotubes. The transitional intensity along the tubular axis is much larger than that perpendicular to the axis for all the nanotubes. The optical gaps of sp(3)-hybridized infinitely-long pentagonal SWSiNTs are near 3.0 eV and 4.7 eV owing to σ-σ* transitions along the direction of the tubular axis. The optical gaps of sp(2)-hybridized infinitely-long armchair SWSiNTs along the tube axis direction are about 0.7 eV and 2.4 eV for Si(3,3) SWSiNTs and 0.7 eV and 2.7 eV for Si(4,4) SWSiNTs. The former peak at 0.7 eV originated from π-π* electron transitions and the latter peak at 2.4 eV or 2.7 eV originated from σ-σ* electron transitions. Meanwhile, the intensities of π-π* electron transitions are stronger than those of σ-σ* electron transitions in SWSiNTs. The low sp(2) transition energy derived from the weak overlap of unpaired p(z) orbitals of silicon atoms. Moreover, the electronic excitations of zigzag SWSiNTs are similar to those of armchair structures. This indicates that sp(2)-hybridized silicon nanotubes possess much greater potential for application in optical fields.     

Characterization of spectroscopic of Pr(DBM)3(TPPO)2 containing poly(methyl methacrylate)

The absorption and fluorescence spectra of Pr(DBM)3(TPPO)2 (DBM: dibenzoylmethane, TPPO: triphenylphosphine oxide) containing poly(methyl methacrylate) (PMMA) were measured. The energy levels are assigned and analyzed in terms of the free-ion Hamiltonian model. From the data available in the absorption spectrum, various spectroscopic parameters such as the spherically symmetric part of the free-ion Hamiltonian (E(AVG)), Slater-Condon (F2, F4, F6), spin-orbit interaction (zeta), Judd-Ofelt (omega2, omega4, omega6) parameters and the reduced matrix elements are derived. The radiative properties of Pr(DBM)3(TPPO)2 containing PMMA were also predicted according to the Judd-Ofelt theory. The values of the fluorescence branching ratio and the emission cross section of 3P0 --> 3F2 fluorescence transition revealed that Pr(DBM)3(TPPO)2 containing PMMA is an efficient luminescent material.     

Optical properties of emeraldine salt polymers from ab initio calculations: comparison with recent experimental data

We present the absorption coefficient alpha(omega), the transverse dielectric function epsilon(omega), the optical conductivity sigma(omega), and the reflectance R(omega) calculated for an emeraldine salt conducting polymer in its crystalline 3D polaronic structure. We utilize Kohn-Sham density functional theory (DFT) electronic wavefunctions and energies implemented in the expression of the macroscopic transverse dielectric function in the framework of the band theory without the electron-hole interaction. Contributions of intra-band transitions are taken into account by adding a Drude-like term to the dielectric function calculated ab initio. Comparison with optical properties, recently measured on high-quality emeraldine salts (Lee, K.; Cho, S.; Park, S. H.; Heeger, A. J.; Lee, C.-W.; Lee, S. H. Nature 2006, 441, 65), and with optical absorption spectra, recorded on other emeraldine salts, is very satisfactory. The calculated spectra are discussed in terms of energy-band structure, density of states, inter- and intra-band transitions, and transverse dielectric function.     

Novel Eu-doped lead telluroborate glasses for red laser source applications

We report the absorption, luminescence and decay analysis of Eu³⁺-doped lead telluroborate (PTBEu) glasses for different Eu³⁺ concentrations ranging from 0.1 to 2.0 mol%. Judd-Ofelt intensity parameters obtained from ⁵D₀→⁷F_J=0-6 emission transitions of Eu³⁺ were used to calculate the radiative transition probabilities, luminescence branching ratios and radiative decay times. The luminescence spectra and decay times were measured at 464 nm excitation. The optical band gap energies are also determined. The luminescence intensity ratio, color purity and emission cross-section values support that the PTBEu20 glass is a suitable candidate for red laser source applications.     

Heavy-metal aromatic rings: cyclopentadienyl anion analogues Sn5(6-) and Pb5(6-) in the Zintl Phases Na8BaPb6, Na8BaSn6, and Na8EuSn6

The title compounds were prepared by direct reactions of the corresponding elements at high temperature. They are isostructural with each other (monoclinic, P2(1)/m, Z = 2; Na(8)BaPb(6), a = 13.116(4), b = 5.351(1), and c = 16.166(5) A, beta = 108.07(2) degrees; Na(8)BaSn(6), a = 12.897(4), b = 5.362(1), and c = 16.826(5) A, beta = 108.19(2) degrees; Na(8)EuSn(6), a = 12.912(2), b = 5.220(1), and c = 15.721(2) A, beta = 108.09(1) degrees ) and contain isolated, flat, and aromatic pentagonal rings of Sn(5)(6)(-) and Pb(5)(6)(-) as well as isolated anions of Sn(4)(-) and Pb(4)(-). According to four-probe conductivity measurements, the tin compounds, Na(8)BaSn(6) and Na(8)EuSn(6), are semiconducting with band gaps of 0.11 and 0.09 eV, respectively, and are therefore electronically balanced. Magnetic measurements show that Na(8)BaSn(6) is diamagnetic while Na(8)EuSn(6) is paramagnetic and undergoes two transitions at low temperatures.     

Accurate solid-state band gaps via screened hybrid electronic structure calculations

The band energy differences of solids calculated with screened hybrid density functionals, such as the functional of Heyd-Scuseria-Ernzerhof (HSE), reproduce experimental band gaps with a high degree of accuracy. This unexpected result is here rationalized by observing that band energy differences obtained from generalized Kohn-Sham calculations with screened (short-range) Hartree-Fock-type exchange approach the excitation energies obtained via time-dependent density functional calculations with the corresponding unscreened functional. The latter are expected to be the accurate predictions of the experimental optical absorption spectra. While the optimum screening parameter (omega) is system dependent, the HSE standard value of omega=0.11 bohr(-1) represents a reasonable compromise across diverse systems.     

K-dependent predissociation dynamics of CS2 in the 210-216 nm region

The dependence of CS2 predissociation upon rotational quantum number K at vibrational levels below the barrier to linearity of the 1B2(1Sigmau+) state has been investigated in detail with laser spectroscopy, by using a heated supersonic source to increase the intensities of hot band transitions. Predissociation lifetimes were determined from rotational contour simulations of 13 vibronic bands in the CS photofragment excitation (PHOFEX) spectrum, each terminating at the same upper vibrational level but via transitions with different K number (K = 0, 1, 2, respectively). The rovibrational populations of CS fragment at these excitation bands were derived from the laser-induced fluorescence (LIF) spectrum, and were used further to obtain the dissociation branching ratios S(1D)/S(3P) as well as the excess energy partitionings after dissociation. The lifetimes and the branching ratios were found to be sensitively dependent on quantum number K; the lifetime decreases with the increase of K, and the branching ratio increases with K. Analysis shows that quantum number K influences the S(1D) channel more effectively than the S(3P) channel. About 28 and 15% of the total available energy is taken up by the CS vibrational and rotational degrees of freedom, respectively. Systematic analysis indicates that the two electronic states interacting with 1B2(1Sigmau+) state should be bent, and the state correlating with S(1D) channel should be more bent.     

Study of the Electronic Structure of Ni(eta(5)-C(5)H(5))(NO) by Variable-Photon-Energy Photoelectron Spectroscopy and Density Functional Calculations

Photoelectron spectra, with photon energies varying from 18 to 120 eV, have been measured for Ni(eta(5)-C(5)H(5))(NO). Relative partial photoelectron cross sections and branching ratios have been evaluated for the first three valence ionization bands. He I and He II photoelectron spectra have been remeasured for Ni(eta(5)-C(5)H(5))(NO) and Ni(eta(5)-C(5)H(4)CH(3))(NO). In the latter case, the fine structure on the first band differs from that in the previously published spectrum. Density functional calculations have been carried out to determine the ionization potentials of the lowest lying states of Ni(eta(5)-C(5)H(5))(NO) as well as the corresponding photoionization cross sections and the resulting branching ratios using the LCGTO-DF and LDKL-DF methods, respectively. Both experimental and theoretical investigations lead to an ion state ordering (2)E(1) < (2)E(2) approximately (2)A(1)< (2)E(1) and an assignment of (2)E(1) states to the first and third bands with the (2)A(1) and (2)E(2) states comprising the second band. This differs from the original assignment in the literature, where the (2)A(1) ionization was assigned to a high-energy shoulder on the first band. The separation of this shoulder from the main band maximum of 0.23 eV (1850 +/- 81 cm(-)(1)) suggests that it may be caused by excitation of the NO stretching vibration in the ion. The neutral molecule has a NO stretch of 1832 cm(-)(1); the calculated energies for the neutral molecule and the cation are 1845 and 1911 cm(-)(1), respectively. Agreement between calculated and experimental ionization energies and good matching of the theoretical and measured branching ratios support the new assignment of the photoelectron spectrum.     

Optical absorption and EPR studies on some natural carbonate minerals

Limestone and dolomite minerals have been investigated by EPR and optical absorption studies. The optical absorption results indicate the presence of ferrous and ferric ion in both the minerals. The bands observed at 24,750, 22,780, 19,415 and 14,450cm(-1) are assigned to 6A1-->4T2 (4D), 6A1-->4E, 4A1 (4G), 6A1-->4T2 (4G) and 6A1-->4T1 (4G) d-d transitions of Fe3+ ions, respectively. A low energy band at 10,638cm(-1) is identified as being due to Fe2+ ion and can be attributed to 5T2g-->5E(g) transition. The weak band in the region 30,000-40,000cm(-1) corresponds to Fe-O charge transfer. Crystal field and Racah parameters evaluated for the Fe2+ ion are Dq=990cm(-1), B=885cm(-1) and C=3860cm(-1) and that for Fe3+ ions are Dq=1040cm(-1), B=703cm(-1) and C=3150cm(-1). The room temperature 9 and 35GHz EPR spectra of the minerals exhibit a sextet hyperfine pattern characteristic of Mn2+. The EPR parameters obtained for Mn2+ in limestone are g=2.00399, A= -9.411mT, D= -8.19mT and these values confirm that the Mn2+ ion are located in the calcite impurity. For Mn2+ in dolomite are g=2.0004, A= -9.45mT for Mn2+ substituted in the Ca lattice site and g=2.00984, A= -9.37mT, D= -9.94mT for substitution at the Mg site. The EPR spectra of heat-treated limestone and dolomite samples at 950 degrees C show a signal corresponding to CO2(-) ion.     

Structural investigations on sodium-lead borophosphate glasses doped with vanadyl ions

Electron paramagnetic resonance (EPR), optical absorption, and FT-IR spectra of vanadyl ions in the sodium-lead borophosphate (Na(2)O-PbO-B(2)O(3)-P(2)O(5)) (SLBP) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO(2+) ions. The spin Hamiltonian parameters g and A are found to be independent of the V(2)O(5) content and temperature. The values of the spin Hamiltonian parameters indicate that the VO(2+) ions in SLBP glasses are present in octahedral sites with tetragonal compression. The population difference between Zeeman levels (N) is calculated as a function of temperature for an SLBP glass sample containing 1.0 mol % VO(2+) ions. From the EPR data, the paramagnetic susceptibility (χ) is calculated at different temperatures, and the Curie constant (C) is calculated from the 1/χ versus T graph. The optical absorption spectra of the glass samples show two absorption bands, and they are attributed to V(3+) and V(4+) ions. The optical band gap energy (E(opt)) and Urbach energy (ΔE) are calculated from their ultraviolet absorption edges. It is observed that, as the vanadium ion concentration increases, E(opt) decreases and ΔE increases. The study of the IR absorption spectrum depicts the presence of BO(3), BO(4), PO(3), PO(4), and VO(5) structural units.