Spontaneous Emission Probabilities Research Articles

Ag nanoparticle enhanced radiative behaviour of Eu3+ ions in sol-gel silica matrix

AgNP doped Eu SiO2 glasses were prepared by the sol-gel method with fixed Eu3+ and varying Ag concentrations. The samples have been characterized structurally by XRD, SEM, EDX and TEM. The effects of incorporation of AgNPs on the radiative properties of the Eu3+ in SiO2 matrix are studied with the help of Absorption and Photoluminescence Spectroscopy. Various radiative parameters like oscillator strength, Judd Ofelt intensity parameters, spontaneous emission probabilities, branching ratio, radiative lifetime, emission cross-section etc. are calculated from the observed absorption and photoluminescence spectra using Judd Ofelt theory, whereas the experimental lifetime of 5D0 state of Eu3+ ion and colour chromaticity is estimated from lifetime and CIE 1931 colour chromaticity measurements. The observed enhancement in the absorption and emission intensities of Eu3+ ions are elucidated in the light of enhanced local field in the vicinity of the AgNPs due to the LSPR effect and also the network modifying role of AgNPs.

Influence of Uncertainty of Probabilities of Spontaneous Emission on the Temperature Behavior of the Collisional Self-Broadening Coefficients of Spectral Lines of CO2 Molecules

The influence of deviation of the values of spontaneous emission probability A on the temperature behavior of collisional self-broadening coefficients γ(T) of spectral lines of CO2 molecules has been analyzed for solution of the inverse problem of simultaneous determination of A and γ from an array of absorption coefficients. Investigations have been carried out for two cases: (i) the calculations are performed using A = 0.2022 s–1 (HITRAN2012); (ii) the A values are obtained via minimization of the sum of weighted squared deviations of the absorption coefficients. It is established for the two calculation versions that, when measuring the absorption coefficients with an error of no more than 0.05αmin, the deviation of the functions γ(T) does not exceed 5% in the temperature range of 300–700 K. No causal relationship is observed between parameters γ and A. The least-squares method makes it possible to correctly calculate the temperature dependences of the collisional self-broadening coefficients of CO2 lines at simultaneous determination of parameters γ(T) and A.

Scattering Matrix Method for Calculating the Spontaneous-Emission Probability in Cylindrically Symmetric Structures

A method is developed for analyzing spontaneous-emission modification in cylindrically symmetric structures. A matrix method is developed for cylindrical structures. General expressions for the radiative-recombination rate are derived for an emitter placed at any point on the structure. Quantitative indicators for estimating radiative-recombination enhancement and suppression are determined; they can be considered as modal Purcell factors. An expression for the total Purcell factor is derived for an emission direction perpendicular to the symmetry axes of the medium; as well as an expression for the integral (total) Purcell factor for the emitter at the symmetry axis.

Optimization of rare earth (Er3+) doping level in lead zinc phosphate glass through Judd-Ofelt analysis

We have investigated via Judd-Ofelt (JO) analysis a new system of PbO, ZnO based P2O5 glass in metaphosphate regime spanning a range of Er3+ doping concentration, 0.6–1.0 mol %. The results are compared between as prepared (unannealed) and annealed samples to converge to the optimum doping regime for laser emission. Using the JO parameters, doping dependence of spontaneous emission probability (A), lifetime of excited state (τR) and luminescence branching ratio (β) of Er3+ have been investigated. The largest value of τR = 15.9 ms is achieved for 4I13/2 state in 1% Er doped as prepared sample. Such a value of τR is ~3.5 times larger than those for other Er3+ doped glass systems. A parameter (χ) suitable to compare between 4I11/2 → 4I15/2 and 4I13/2 → 4I15/2 transitions in Er3+ has been proposed. Along with the largest magnitude of τR, the maximum value of χ occurs at the same doping level of 1% in unannealed sample. For 4I13/2 → 4I15/2 emission, 100% of β value occurs. It is shown that all these conditions together with χ > 1 lead to the conclusion that 4I13/2 → 4I15/2 transition (1540 nm) will dominate over 4I11/2 → 4I15/2 emission (987 nm). In the admixed laser emission, 1540 nm component will be the largest at 1 mol % doping for unannealed sample.

Compositional dependence of Stark splitting and spectroscopic properties in Yb3+-doped lead silicate glasses

In this work, we explore the effect of ionic field strength of modifiers (Li+, Na+, K+, Mg2+, Ca2+, Sr2+ and Ba2+) on room-temperature Stark splitting and spectroscopic properties of Yb3+ ions in lead silicate glasses. Our measurements show that the ‘crystal-field’ parameter and asymmetry degree of Yb3+ ion ligands are increased as a function of modifier field strength due to the corresponding higher electronegativity and bonding energy. Higher field strengths produce greater absorption σa and emission σe cross-sections, effective emission linewidth Δλeff and spontaneous emission probability Arad of Yb3+ ions. We report a 57% enhancement on σa, σe and Δλeff by doubling the field strength of the modifier cations, implying Yb3+ ion doped lead silicate glass with high field strength modifiers (Li+, Mg2+ and Ca2+) may be a promising candidate for efficient laser emission operation.

Structural and Judd-Ofelt intensity parameters of a down-converting Ba2GdV3O11:Eu3+ nanophosphors

A white light emitting Barium gadolinium vanadate, Ba2GdV3O11:Eu3+, is developed using time-saving combustion synthesis technique. The Rietveld analysis of the optimum luminescent composition (Ba2Gd0.97V3O11:0.03Eu3+) confirmed that it crystallizes into the monoclinic system with P21/a space group. The calculation of lattice parameters unveiled the unit cell expansion which in turn governed the asymmetry around activator. The photoluminescent analysis showed an efficient energy transfer from vanadate absorption of Ba2GdV3O11 host to Eu3+, resulting in a very intense characteristic emission of the Eu3+. The PL decay investigations of Ba2GdV3O11:0.03Eu3+ nanophosphor gave the radiative lifetime and total spontaneous emission probabilities. Judd-Ofelt parameterization provided the refractive index of the host and stimulated emission cross section for 5D0?7F4 (8.03) transition in Ba2GdV3O11:0.03Eu3+ phosphor. The quantum efficiency of 5D0 state in Ba2Gd0.97Eu0.03V3O11 phosphor was calculated to be 79%, resulting in a pure white emission. All results demonstrate that Ba2Gd0.97V3O11:0.03Eu3+ is a potential candidate for single-phased WLEDs.

Exploration of the new tellurite glass system for efficient 2 μm luminescence

A new TeO2-Ga2O3-BaO (TGB) glass system has been explored to achieve high-efficient luminescence at 2 μm region. The glasses are characterized by wide infrared transmittance range, excellent thermal stability, high density and refractive index, and low maximum phonon energy. Judd-Ofelt analysis reveals high spontaneous emission probabilities of Tm3+ and Ho3+ in this glass host. As a result, intense emissions near 1.8 and 2 μm were realized in the Tm3+-doped and Nd3+/Ho3+ co-doped TGB glasses, respectively. The emission cross-sections of Tm3+ and Ho3+ are 1.024 × 10−20 cm2 and 0.829 × 10−20 cm2 with maximum gain coefficients of 4.51 and 1.55 cm−1, respectively. The combined results indicate that the TGB glass system is a potential host for obtaining high-efficient 2 μm luminescence.

Enhancement of spontaneous emission probability in a disordered media

Was provided statistical analysis of Purcell effect dependence on emission frequency and emitter position in disordered structure. Fact that the presence of disorder in one-dimensional photonic crystals could lead to a modification of spontaneous emission rate in the frequency region corresponding to a photonic band gap (PBG) was demonstrated. Was shown, that amount of disorder regulates the two different regimes of the Purcell effect. In case of weak disorder Purcell enhancement of spontaneous emission occurs at PBG edges, and in case of strong disorder at PBG centre.

Controllable optical properties between Ho3+: 5I7 → 5I8 and Tm3+: 3F4 → 3H6 transitions in germanosilicate glasses

Diode-pumped solid-state 2 μm lasers have seen rapid development for their efficient operation, compact size, and stable performance. In this work, doped germanosilicate (SiO2-GeO2-Ga2O3-Lu2O3) glasses with varying Tm3+/Ho3+ concentrations exhibiting excellent physical and optical characteristics were successfully prepared. Thermal and structural properties were analyzed by the measured DSC and Raman spectra. An evident efficient wide absorption band near 770–830 nm demonstrated the feasible energy transfer between Tm3+: 3F4 → 3H6 and Ho3+: 5I7 → 5I8 transitions. Meanwhile, combining with Judd-Ofelt theory, super predicted spontaneous emission probabilities were obtained, which are beneficial to obtain fine laser action for solid-state lasers. This is a first study to demonstrate that a tunable fluorescence peak (1.8–2.05 μm) can be obtained by modulating the combined effects between two luminous activation centers. Therefore, the results indicate a promising rare-earth doped glass host for solid-state 2 μm lasers.

Quantization of the Electromagnetic Field in Three-Dimensional Photonic Structures on the Basis of the Scattering Matrix Formalism (S Quantization)

A technique for quantization of the electromagnetic field in photonic nanostructures with three-dimensional modulation of the dielectric constant is developed on the basis of the scattering matrix formalism (S quantization in the three-dimensional case). Quantization is based on equating the eigenvalues of the scattering matrix to unity, which is equivalent to equating each other the sets of Fourier expansions for the fields of the waves incident on the structure and propagating away from the structure. The spatial distribution of electromagnetic fields of the modes in a photonic nanostructure is calculated on the basis of the R and T matrices describing the reflection and transmission of the Fourier components by the structure. To calculate the reflection and transmission coefficients of individual real-space and Fourier-space components, the structure is divided into parallel layers within which the dielectric constant varies as a function of two-dimensional coordinates. Using the Fourier transform, Maxwell’s equations are written in the form of a matrix connecting the Fourier components of the electric field at the boundaries of neighboring layers. Based on the calculated reflection and transmission vectors for all polarizations and Fourier components, the scattering matrix for the entire structure is formed and quantization is carried out by equating the eigenvalues of the scattering matrix to unity. The developed method makes it possible to obtain the spatial profiles of eigenmodes without solving a system of nonlinear integro-differential equations and significantly reduces the computational resources required for calculating the probability of spontaneous emission in three-dimensional systems.

Spectroscopic investigation of Er3+ doped BaF2 single crystal

We report on the spectroscopic investigation of Er3+ doped BaF2 single crystals. High-quality crystals have been gown by the Bridgman-Stockbarger pulling technique. The room temperature absorption, excitation, emission and fluorescence decay spectra of the luminescent Er3+ ions inserted in BaF2 fluoride single crystals have been investigated. Using the Judd-Ofelt (JO) theory, the intensity parameters of Er3+ ions have been calculated to be Ω2 = 0.949 × 10−20 cm2, Ω4 = 0.975 × 10−20 cm2 and Ω6 = 1.258 × 10−20 cm2. These parameters were then used to calculate the radiative transition probabilities (AJJ′), branching ratios (βJJ′) and radiative lifetimes (τrad) of the main laser emitting levels of Er3+ ions. The obtained spectroscopic properties are compared to those of Er3+ transitions in other fluoride and oxide hosts. The excitation spectrum in the UV–Visible spectral range is very close to the absorption spectrum indicating that all observed absorption levels can excite the Erbium green emission. The emission spectrum is mainly dominated by the green emission alongside a weak red emission. For the main transitions, there is a good agreement between the emission spectrum and the spontaneous emission probabilities given by the JO analysis. Using the Fuchtbauer–Ladenburg method, the emission cross-section of the three main visible emission were determined in addition to other important laser parameters such radiative quantum efficiency and optical gain.

Thermal Stability and Spectral Properties of Tm3+-Yb3+ CO-Doped Tellurite Glasses

Glasses of the system 75TeO2–20ZnO–5La2O3–0.8Tm2O3–xYb2O3 were prepared by high temperature melt cooling method. Results of differential scanning calorimetry indicate that, all glass samples have excellent thermal stability. Judd–Ofelt strength parameters, spontaneous emission probabilities, fluorescence branching rations, fluorescence radiative lifetime of Tm3+ ions in tellurite glass were calculated. The impact of Yb3+ concentration on the fluorescence properties of Tm3+ ions in the S band under the pumping wavelength of 465 nm was investigated in a suggestion that, 3H4 radiative lifetimes will be prolonged and the performance of optical amplifier gain of Tm3+ in tellurite glass co-doped with 0.5 mol % Yb3+ ions will be improved.

Concentration dependent spectroscopic behavior of Sm3+-doped sodium fluoro-phosphates glasses for orange and reddish-orange light emitting applications

Sodium fluoro-phosphate (NNS) glasses doped with different concentrations of Sm3+ ions have been prepared using conventional melt quenching technique and characterised for their lasing potentialities using spectroscopic techniques such as Raman, optical absorption, emission and emission decay measurements. The structures of glasses were investigated by X-ray diffraction (XRD) and Raman spectroscopy to understand their dependence of structure on composition. Absorption spectrum from near infrared to visible was obtained and the Judd–Ofelt (J-O) intensity parameters (Ω2, Ω4, and Ω6) were determined. Spontaneous emission probabilities of some relevant transitions, branching ratio, and radiative lifetimes of several excited states of Sm3+ have been predicted using intensity J-O parameters. The luminescence intensity decreases with the increase in Sm3+ ion concentration beyond 0.5 mol% and the same was discussed through various energy transfer mechanism which takes place between Sm3+ ions. The lasing parameters like peak stimulated emission cross-section (σep), branching ratios (βR), measured branching ratios (βexp) and radiative lifetime (τrad) for the excited 4G5/2 luminescent level have been calculated, discussed and reported. The measured lifetime (τmeas) of the 4G5/2 excited level is found to be single exponential up to 0.5 mol% and after that it changes into non-exponential for higher concentration and the non-exponential behavior arises due to the energy transfer between the Sm3+ ions through various cross-relaxation channels. The non-exponential decay rates, at higher concentrations, were fitted to Inokuti–Hirayama (IH) model for S = 6 which reveals that the energy transfer process is of dipole–dipole in nature. The R/O intensity ratios have been studied by varying the RE ion concentration and further CIE color chromaticity coordinates have also been calculated to characterize the emission of the prepared glasses. Using the Mc-Cumber method, emission cross-section (σem), Absorption cross-section (σa), and gain cross-section (G(λ)) for the 6F9/2→6H5/2 transition, were calculated.From the emission characteristic parameters of 4G5/2 level, it is concluded that the NNS glasses could be useful for photonic devices like visible lasers, fluorescent display devices and optical amplifiers.

Er3+-doped fluorozirconate glass modified by PbF2 with high stimulated emission cross-section

Er3+-doped fluoride glass modified by PbF2 is developed. Upon 980 nm laser-diode excitation, intense luminescence emission around 2.71 μm from the Er3+4I11/2 → 4I13/2 transition is observed. On the basis of the Judd–Ofelt theory, the intensity parameters and radiative properties are determined from the absorption and emission spectra. Compared with conventional Er3+-doped fluoride glass (Er:ZBLAN), the proposed glass possesses a large spontaneous emission probability (Arad, 29.76 s−1) and a high stimulated emission cross-section (σem) at 2.71 μm (1.25 × 10−20 cm2). In addition, fibers with high strength might be drawn from the glass preform owing to its good chemical stability; therefore, it may be useful for increasing the output power of mid-infrared lasers. The results indicate that the present glass can be a good candidate for mid-infrared fiber lasers.

Luminescence properties of Eu3+ doped CdF2 single crystals

This paper reports the photoluminescence properties of Eu3+ doped CdF2 single crystals. The pulled crystals were prepared by use of the Bridgman technique from a vacuum furnace in fluoride atmosphere. Absorption, excitation and emission spectra of the crystal doped with three Eu3+ concentrations (0.02%, 0.1% and 0.6% mol.) were recorded at room temperature. The emission spectra exhibit a strong yellow and red emissions in the spectral range 550–720 nm which are assigned to 5D0 → 7FJ (J = 1, 2, 4) transitions and a weak infrared emission around 816 nm corresponding to 5D0 → 7F6 transition. The magnetic dipole emission (5D0 → 7F1) is the most intense for each Eu3+ concentration.The Judd-Ofelt intensity parameters Ω2, Ω4, Ω6 for 4f-4f transitions of Eu3+ ions were computed from the emission spectra using the 5D0 → 7FJ (J = 1, 2, 4, 6) transitions. Via these phenomenological intensity parameters, the spontaneous emission probabilities, branching ratios, radiative lifetimes, quantum efficiencies and emission cross-sections for the main Eu3+ emitting levels are evaluated.

Investigation of excited states populations density of Hall thruster plasma in three dimensions by laser-induced fluorescence spectroscopy

The article deals with investigation of the excited states populations distribution of a low-temperature xenon plasma in the thruster with closed electron drift at 300 W operating conditions were investigated by laser-induced fluorescence (LIF) over the 350–1100 nm range. Seven xenon ions (Xe II) transitions were analyzed, while for neutral atoms (Xe I) just three transitions were explored, since the majority of Xe I emission falls into the ultraviolet or infrared part of the spectrum and are difficult to measure. The necessary spontaneous emission probabilities (Einstein coefficients) were calculated. Measurements of the excited state distribution were made for points (volume of about 12 mm3) all over the plane perpendicular to thruster axis in four positions on it (5, 10, 50 and 100 mm). Measured LIF signal intensity have differences for each location of researched point (due to anisotropy of thruster plume), however the structure of states populations distribution persisted at plume and is violated at the thruster exit plane and cathode area. Measured distributions show that for describing plasma of Hall thruster one needs to use a multilevel kinetic model, classic model can be used just for far plume region or for specific electron transitions.

Квантование электромагнитного поля в трехмерных фотонных структурах на основе формализма матрицы рассеяния (S-квантование)

AbstractA technique for quantization of the electromagnetic field in photonic nanostructures with three-dimensional modulation of the dielectric constant is developed on the basis of the scattering matrix formalism ( S quantization in the three-dimensional case). Quantization is based on equating the eigenvalues of the scattering matrix to unity, which is equivalent to equating each other the sets of Fourier expansions for the fields of the waves incident on the structure and propagating away from the structure. The spatial distribution of electromagnetic fields of the modes in a photonic nanostructure is calculated on the basis of the R and T matrices describing the reflection and transmission of the Fourier components by the structure. To calculate the reflection and transmission coefficients of individual real-space and Fourier-space components, the structure is divided into parallel layers within which the dielectric constant varies as a function of two-dimensional coordinates. Using the Fourier transform, Maxwell’s equations are written in the form of a matrix connecting the Fourier components of the electric field at the boundaries of neighboring layers. Based on the calculated reflection and transmission vectors for all polarizations and Fourier components, the scattering matrix for the entire structure is formed and quantization is carried out by equating the eigenvalues of the scattering matrix to unity. The developed method makes it possible to obtain the spatial profiles of eigenmodes without solving a system of nonlinear integro-differential equations and significantly reduces the computational resources required for calculating the probability of spontaneous emission in three-dimensional systems.

Spectroscopic properties and Judd–Ofelt analysis of Eu3+ in Y4Al2O9 crystals

Optical absorption, excitation and emission spectra of Eu3+ ions in Y4Al2O9 were investigated. Judd-Ofelt intensity parameters for f-f transitions were derived from the emission spectra and also from the integrated absorption spectra. These parameters were used to calculate the total spontaneous emission probabilities (AR), lifetimes (τR) and branching ratios (βR) for 5D0 excited state of Eu3+. The calculated values of τR and βR are compared with the measured values for 5D0 level. The stimulated emission cross-sections σ were also evaluated for the 5D0 → 7FJ transitions for the first time in this system.

Purcell effect in complex photonic structures based on optical Fibonacci lattices

The modification of probability of spontaneous emission for a dipole emitter that placed in Fibonacci lattice-based palindrome structures was examined. Localization properties of eigenstates, that appears in photonic band gaps of palindrome structure was investigated. It was shown, that for a dipole placed in centre of palindrome structure an increase in the spontaneous emission rate will be observed and, in addition, calculated value of Purcell factor is significantly greater than for critical localized states of usual Fibonacci lattices, and close to microcavity eigenmode case.

Enhancement of spectroscopic and luminescence properties of Er3+ doped tellurite glasses by adding P2O5 for lasing materials

Er3+-doped phosphor-tellurite glasses has been synthesized by conventional melting method. Results of differential scanning calorimetry (DSC) measurements indicate a good thermal stability of tellurite glasses. The DSC measurements show an improvement of thermal stability of glass hosts after adding P2O5. The structures of glasses were investigated by X-ray diffraction (XRD) and Raman spectroscopy to understand their dependence of structure on composition. Absorption spectrum from near infrared to visible was obtained and the Judd–Ofelt (J-O) intensity parameters (Ω2, Ω4, and Ω6) were determined. Spontaneous emission probabilities of some relevant transitions, branching ratio, and radiative lifetimes of several excited states of Er3+ have been predicted using intensity J-O parameters. Up-conversion luminescence characteristics, under 977 nm excitation wavelength, have been investigated at room and low temperature in these glasses. Intense green and red emissions from Er3+ centered at 534 nm, 548 nm and 660 nm, corresponding to the transitions 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2, respectively, were simultaneously observed. The quadratic dependence of the up-conversion emission on the excitation power indicates that two-photon steps are involved for the three visible emission bands. The PL lifetimes is found to decrease in the temperature range 77–300K. Using the Mc-Cumber method, emission cross-section (σe), Absorption cross-section (σa), and gain cross-section (G(λ)) for the 4I13/2→4I15/2 transition, were calculated. By analyzing obtained data based to all advantages after adding P2O5, the tellurite glasses can be used as potential host material for developing optical amplifiers applied for 1.53 µm band broad and high-gain erbium-doped fiber amplifiers (EDFA).