Peak Stimulated Emission Cross-section Research Articles

Liquid phase epitaxy growth and visible emission of Tb3+,Gd3+:LiYF4 layers

Single-crystalline layers of 12 at.% Tb3+, 5 at.% Gd3+:LiYF4 were grown by the liquid phase epitaxy method on (001) oriented bulk undoped LiYF4 substrates using LiF as a solvent. The growth temperature was 737–740 °C, the growth duration was 15 - 25 min, and the layer thickness was 40–90 µm. The structural, morphological, vibronic and spectroscopic properties of the layers were studied. Tb3+ ions were uniformly distributed in the layers with no diffusion into the substrate. Polarized Raman spectroscopy confirmed the orientation of the layers (growth along the [001] direction). Under excitation in the blue, the layers exhibited intense green emission. For the 5D4 → 7F5 Tb3+ transition, the peak stimulated-emission cross-section is 1.28 × 10−21 cm2 at 542.0 nm for π-polarization. The luminescence lifetime of the 5D4 Tb3+ state is 5.05 ms at room temperature. The crystal-field splitting of Tb3+ multiplets was determined at low temperature. The developed epitaxies are promising for green and yellow waveguide lasers.

Stimulated emission cross sections and temperature‐dependent spectral shifts of neutral nitrogen‐vacancy centers in diamonds

AbstractThe neutral nitrogen‐vacancy (NV0) defects in diamond are photostable color centers, suitable for a wide range of applications in science and engineering. However, the photophysical properties of the centers have not yet been fully characterized. This work measured the stimulated emission cross sections of NV0 in a single‐crystal diamond by two‐photon excitation of its matrix at 344 nm. From the measured photoluminescence spectrum and the fluorescence lifetime of 20 ± 1 ns, we determined a peak stimulated emission cross section of 1.43 ± 0.07 × 10−17 cm2 at 650 nm for the NV0 centers. In addition, we have also examined the thermal shifts of the zero‐phonon line of NV0 centers in nanoscale diamonds (~100 nm in diameter) over the temperature range of 30–120°C. A temperature measurement sensitivity of 0.2 K·Hz−1/2 was achieved, which is about two‐fold better than that of NV−, despite that the fluorescence intensity of NV0 is about six‐fold lower than that of NV− in the same nanoparticles. The result is attributed to the smaller electron–phonon coupling strength of the neutral center, compared with its negatively charged counterpart.

Spectroscopic study of Er-doped Ga2Ge5S13 glass for mid-IR laser applications

We present mid-IR spectroscopic characterization of the low-phonon chalcogenide glass, Ga2Ge5S13 (GGS) doped with Er3+ ions. Under the excitation at ∼800 nm, Er3+:GGS exhibited broad mid-IR emission bands centered at ∼2.7, ∼3.5, and ∼4.5 µm at room temperature. The emission lifetime of the 4I9/2 level of Er3+ ions in GGS glass was found to be millisecond-long at room temperature. The measured fluorescence lifetimes were nearly independent of temperature, indicating negligibly small nonradiative decay rate for the 4I9/2 state, as can be expected for a low-maximum-phonon energy host. The transition line-strengths, radiative lifetimes, fluorescence branching ratios were calculated by using the Judd-Ofelt method. The peak stimulated emission cross-section of the 4I9/2 → 4I11/2 transition of Er3+ ion was determined to be ∼0.10×10−20 cm2 at room temperature.

Spectroscopic investigation of dysprosium doped BaF2 single crystals pertaining to the 3 µm mid-IR laser potential

We present the results of a comprehensive spectroscopic investigation pertaining to laser potential evaluation of the 3-micron Dy3+ mid-IR transition in the low-maximum phonon energy host barium fluoride (BaF2). This investigation involved absorption, fluorescence, and decay time measurements, recorded for a range of temperatures. Laser-relevant parameters such as absorption and stimulated-emission cross sections, quantum-efficiencies, and radiative lifetimes were determined for room temperature (300 K) and liquid nitrogen temperature. The peak stimulated emission cross section was found to be 0.45×10−20 cm2 at room temperature and 1.58×10−20 cm2 at 77 K. The gain cross sections, predictive of laser potential, were also derived. Finally, an examination of the nature of the non-radiative decay rates as a function of temperature was performed, showing the degree to which multi-phonon relaxation and other non-radiative pathways affect the overall fluorescence behavior.

Polarized spectroscopic properties of disordered Er3+:Gd2SrAl2O7 crystal

A multi-position disordered Er3+:Gd2SrAl2O7 single crystal was grown by the Czochralski method. Room temperature polarized spectral properties of the crystal were investigated in detail. The Judd–Ofelt theory was applied to analyze the polarized absorption spectra. The peak stimulated emission cross-sections of the 4I13/2→4I15/2 transition reach 0.79 ×10−20 and 1.25×10−20 cm2 for σ and π polarizations, respectively. The gain curves are flat with full widths at half the maximum larger than 60 nm. Fluorescence lifetimes of the 4I13/2 multiplet for Er3+ ions were fitted to be 4.93 ms and 3.48 ms from measured fluorescence decay curves for bulk and powder samples, respectively. The results show that the Er3+:Gd2SrAl2O7 crystal may be a potential gain medium for a 1.55 µm laser with low pumping threshold.

Thermal Correction of Eu3+doped Na2O-Al2O3-P2O5 Glasses System

Abstract Optical absorption, excitation, emission spectra and lasing potential of sodium aluminium phosphate (Na2O-Al2O3-P2O5) glasses doped with Eu3+ ions were studied and discussed. These glasses were synthesized by melt-quenching technique at 1200 °C. It was found that the emission spectra of glass samples exhibited an intense red (612 nm) emission band upon excitation with 394 nm. Judd-Ofelt (JO) intensity parameters (Ωλ=2,4,6), radiative transition probabilities (AR), peak stimulated emission cross-sections (σ(λp)) and branching ratio (β) were calculated and compared between without and with thermal corrections. The evaluated JO values indicated that, this glass perform high potential for using as red laser medium application

Peak stimulated emission cross sections and quantum efficiencies of Sm3+ and Sm3+-Eu3+ co-doped bismuth boro-tellurite glasses

The effect of host glass composition and co-doping with Eu3+ on the optical properties of Sm3+ has been investigated in bismuth boro-tellurite glasses. The intensity parameters Ωt (t = 2,4,6), radiative transition probability (Arad) and radiative lifetimes (τrad) are obtained from optical absorption studies. Excitation spectra show that there exists energy transfer from Sm3+ to Eu3+ and vice versa. From fluorescence studies, fluorescence decay time (τexp), radiative quantum efficiencies (η), branching ratios (β) and peak stimulated emission cross section (σp) are obtained. The highest η of Sm3+ doped bismuth boro-tellurite glasses is found to be 60% and for Sm3+-Eu3+ co-doped glasses, it is 74%. Changing the host glass composition and co-doping with Eu3+ ions, the η of the glasses can be improved. The σp of Sm3+-Eu3+ doped glasses is found to be larger than that of singly doped Sm3+ glasses. Our results indicate that modifying the host glass composition and co-doping with Eu3+ can improve the emission characteristics of Sm3+ ions. Bismuth boro-tellurite glasses with enhanced values for η and σp are suitable for photonic devices and photovoltaic applications.

Ba5Zn4Gd8O21:Tb3+—structural characterization and the Judd-Ofelt parameterization from emission spectra

Ba5Zn4Gd8O21:Tb3+ nanorods; synthesized via solution combustion route; were found to crystallize in the tetragonal (I4/m, 87) crystal system. The UV excitation at 290 nm of all Ba5Zn4Gd8O21:Tb3+ samples yielded the characteristics emission corresponding to 5D4 → 7F6,5,4,3 transitions in Tb3+ activator (used for Judd-Ofelt analysis). A detailed investigation of photoluminescence decay curves and emission spectra of Ba5Zn4Gd8O21:Tb3+ nanorods provided the radiative lifetime (1.0889 ms) and total radiative transition rates from 5D4 state in Tb3+ ion. The electric-dipole radiative transition probabilities (extracted from total radiative rates i.e. electric-dipole + magnetic-dipole) were used to calculate the Judd–Ofelt intensity parameters (Ω2 = 4.76 × 10−20, Ω4 = 2.11 × 10−20 and Ω6 = 2.00 × 10−20 cm2). The very high quantum efficiency of 5D4 state (81%) suggests their potential use in lighting and display devices. Finally, a large magnitude of peak stimulated emission cross section of 5D4 → 7F5 (16.5838 × 10−20 cm2) transition also claims their promising candidature as a good laser material.

Spectroscopic properties and continuous-wave laser performance of Yb:Gd2SrAl2O7 crystal

In this paper, the crystal growth, spectral properties, and laser performance of 5 at.% Yb doped Gd2SrAl2O7 (Yb:GSAO) crystal were reported. The peak absorption cross-section is 5.22 × 10−20 cm2 at 979 nm and the peak stimulated emission cross section calculated by Füchtbauer-Ladenburg (FL) method is 1.22 × 10−20 cm2 at 1062 nm for the π polarization. Efficient continuous-wave (cw) laser action was demonstrated in the range of 1060.2–1069.5 nm with a c-cut crystal sample end pumped by a 980 nm laser diode, generating a maximum output power of 7.345 W with an optical-to-optical efficiency of 47.5% and a slope efficiency of 53.7%. The results indicate that Yb:GSAO is a good Yb laser material.

Raman and photoluminescence studies of europium doped zinc-fluorophosphate glasses for photonic applications

Europium (Eu3+)-doped zinc-fluorophosphate (PKAZfEu) glasses have been synthesized by usual melt-quenching technique. Optical absorption, photoluminescence excitation, photoluminescence and decay curves of these glasses were measured at room temperature and investigated. The Judd-Ofelt (JO) parameters (Ωλ, λ = 2 and 4) were determined from the measured emission spectra and used for quantifying the radiative parameters that include radiative transition probability (AR), radiative lifetime (τR), branching ratios (βR), effective bandwidths (∆λeff) and peak stimulated emission cross-section (σ(λP)) for the 5D0 luminescent state of Eu3+. The electron-phonon coupling strength and phonon energy of the glasses were obtained from the phonon sideband spectrum. The chromaticity coordinates for different concentration of PKAZfEu glasses were evaluated by analyzing the emission spectra with Commission International de l'Eclairage (CIE) color diagram. Decay curves of Eu3+ ions for the 5D0 → 7F2 transition have been obtained under 393 nm excitation. The decay curves exhibit a single exponential behavior for all the investigated glasses. Luminescence properties of Eu3+ ion for the 5DO → 7F2 transition indicate that the PKAZfEu glasses could be a suitable gain medium for visible red lasers and display devices.

Spectral properties of Nd3+ ions in the new fluoride glasses with small additives of the phosphates

A series of the new fluoride glasses with small additives of the phosphates doped with different of Nd3+ content is developed. The dopant concentration dependence of optical absorption and emission properties is reported here for the concentration range of 2.5×1020 to 1.0×1021 (ions/cm3). Using the Judd-Ofelt theory the phenomenological intensity parameters Ωt (t = 2; 4; 6) were obtained for all glasses studied. Fluorescence lifetime, quantum efficiency and nonlinear refractive index n2. were obtained. The peak stimulated emission cross sections of the transitions at 899 nm, 1053 nm and 1320 nm were calculated according to J-O theory. The stimulated emission cross-sections of 4F3/2→4I9/2,4F3/2→4I11/2 and 4F3/2→4I13/2 transitions were determined by the Fuchtbauer-Landenburg equation (FL) and the modified reciprocity method (MR) for all Nd3+concentrations. The analysis of the luminescence quenching depending on the concentration of the activator was carried out. It was concluded that present fluoride glass with small additives of phosphates is a promising material for laser applications.

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.

Optical spectroscopy and luminescence properties of Ho3+ doped zinc fluorophosphate (ZFP) glasses for green luminescent device applications

Ho3+ doped zinc fluorophosphate (ZFP) glasses with molar chemical compositions, (60-x) NH4H2PO4+20ZnO+10BaF2+10NaF+xHo2O3 (where x = 0.1, 0.3, 0.5, 1.0 and 1.5 mol%) were prepared by melt quenching technique. These glasses were characterized through physical, structural, optical, excitation, luminescence and decay curve analysis. From the absorption spectra, spectral intensities (fexp and fcal), Judd-Ofelt intensity parameters (Ω2, Ω4 and Ω6), radiative transition probabilities (AT), radiative lifetimes (τR) and branching ratios (βR) were evaluated for all Ho3+ doped ZFP glass matrices. From the photoluminescence spectra, peak stimulated emission cross-sections (σP) were calculated for all Ho3+ doped ZFP glasses. The Ho3+ doped ZFP glasses show strong green emission at 545 nm and red emission at 656 nm under excitation, 450 nm. The measured lifetimes (τmeas) of (5S2)5F4 level of Ho3+ doped ZFP glasses were obtained from decay profiles. The CIE color coordinates of Ho3+ doped ZFP glasses were calculated from emission spectra and 1.0 mol% of Ho3+ doped ZFP glass matrix gives green emission. Hence, these results confirm that the Ho3+ doped ZFP glasses could be considered as a promising candidate for visible green laser applications.

Laser spectroscopy of NV- and NV0 colour centres in synthetic diamond

In this paper, we analyse the prospects for using nitrogen-vacancy centre (NV) containing diamond as a laser gain material by measuring its key laser related parameters. Synthetic chemical vapour deposition grown diamond samples with an NV concentration of ~1 ppm have been selected because of their relatively high NV concentration and low background absorption in comparison to other samples available to us. For the samples measured, the luminescence lifetimes of the NV- and NV0 centres were measured to be 8 ± 1 ns and 20 ± 1 ns, respectively. The respective peak stimulated emission cross-sections were (3.6 ± 0.1) × 10−17 cm2 and (1.7 ± 0.1) × 10−17 cm2. These measurements were combined with absorption measurements to calculate the gain spectra for NV- and NV0 for differing inversion levels. Such calculations indicate that gains approaching those required for laser operation may be possible with one of the samples tested and for the NV- centre.

Crystal growth, polarized spectra, and laser performance of Yb:CaGdAlO4 crystal

In this paper, the crystal growth, polarized spectra, and laser performance of Yb:CaGdAlO4 crystal were reported. The segregation coefficient of Yb3+ ions was calculated to be 0.47. The cell parameters were determined to be a = b = 0.3658 nm, c = 1.1985 nm. The peak absorption cross-section was calculated to be 2.65 × 10−20 cm2 at 979 nm and the peak stimulated emission cross-section was 2.23 × 10−20 cm2 at 980 nm for the π polarization. The continuous-wave (CW) laser operations of uncoated Yb:CaGdAlO4 crystals with 5 × 5 × 3 mm3 in size were demonstrated. A maximum output power of 1.6 W at 1048 nm was obtained with a slope efficiency of 28%. The results show that Yb:CaGdAlO4 crystal is a promising laser medium.

2–3 μm emission and fluorescent decaying behavior in Ho3+-doped tellurium germanate glass

In this work, we report the 2.05μm emission and ∼3μm broadband spectra of Ho2O3-doped 33GeO2–30TeO2–27PbO–10CaO (in mol%) glass under 640nm laser excitation. Clear emission spectra due to the 5I7–5I8 transition and the 5I6–5I7 transition in Ho3+ are observed. The 2.05μm emission intensity and the full width at half maximum (FWHM) of the ∼3μm broadband depend on the Ho concentration. The peak stimulated emission cross-section of Ho3+ is 6.57×10−21cm2 at 2.05μm, as calculated by the McCumber theory. The emission spectra are recorded and the maximum emission intensity at 2.05μm is obtained at a doping level of 0.5mol% Ho2O3 in the glass. A broad and flat emission band from 2700nm to 3050nm is observed in 2mol% Ho2O3-doped tellurium germanate glass. The lifetime of the 5I7 state decreases with the increase in Ho3+ concentration due to non-radiative relaxation processes. An energy transfer coefficient of 271.88mol−1s−1 is obtained.

Dy3+-doped tellurite based tungsten-zirconium glasses: Spectroscopic study

Tellurite based tungsten zirconium glasses-doped with trivalent dysprosium (Dy3+) ions (TWZDy) have been prepared by conventional melt-quenching technique and characterized through thermal, structural and spectroscopic measurements. XRD pattern of the glass confirms its amorphous nature. The functional groups of the TeO3 and TeO4 units along with WO− and ZrO vibrations have been identified from Fourier transform infrared spectrum. The energy level analysis has been carried out by using the parametric free-ion Hamiltonian model. Judd–Ofelt theory has been used to explore the spectral intensities of Dy3+ ions in the present glass system. From the emission spectra, the emission intensities increases from 0.05 to 1.0mol% of Dy3+ ion and then decreases for higher concentrations due to energy transfer between Dy3+ ions. The higher value of peak stimulated emission cross-section (40.46×10−22cm2), noticed for 4F9/2→6H13/2 transition, is comparable with other reported Dy3+ systems. The TWZDy glasses emit intense yellowish-white color (x=0.32; y=0.44) which is nearer to standard white light zone. The decay curves exhibit single exponential nature at lower concentrations (⩽0.1mol%) and turns into non-exponential (⩾0.5mol%) due to energy transfer processes. In order to unravel the energy transfer process the non-exponential decay curves have been fitted to Inokuti–Hirayama (IH) model with S=6. The analyses of the results indicate that the present TWZDy glasses are suitable for luminescent display device applications as well as for white light generation.

Judd Ofelt Analysis and Optical Properties of Eu\(^{3 + }\) Doped Tellurite Glasses

In this work, the structural characteristic and photoluminescence properties of Eu\(^{3 + }\) doped B\(_{2}\)O\(_{3}\)-TeO\(_{2}\) -ZnO-Na\(_{2}\)O glasses were investigated. These glasses were prepared by a melting method in air, combined with thermal annealing at 350\(^{\circ}\)C, 450\(^{\circ}\)C and 550\(^{\circ}\)C for different duration times. The structural analysis results of these glasses revealed the formation of micro-crystals in the annealed host glass. The photoluminescence spectra of Eu\(^{3 + }\) doped in these samples were observed. The local vibration mode around Eu\(^{3 + }\) ions was investigated by the phonon side-band (PSB) associated with \(^{7}\!F_{0}-^{5}D_{2}\) transition of Eu\(^{3+}\). Judd-Ofelt parameters were then evaluated based on photoluminescence spectra and the luminescence intensity ratios of \(^{5}D_{0} \to ^{7}\!F_{J}\) (\(J=2, 4\) and 6) to \(^{5}D_{0} \to ^{7}\!F_{1}\) transition were predicted. The obtained results were then used to calculate \(\Omega _{2},\;\Omega _{4},\; \Omega _{6} \) parameters based on Judd-Ofelt theory. These \(\Omega _{2}\), \(\Omega _{4}\), \(\Omega _{6}\) parameters allow to derive radiative properties of Eu\(^{3 + }\) ions in glass material such as transition probabilities, radiative lifetimes and peak stimulated emission cross-section for the \(^{5}D_{0} \to ^{7}\!F_{J}\) transitions.

Optical characterization, infrared emission and visible up-conversion in Er3 + doped tellurite glasses

In this work, Er3+ doped tellurite glasses have been prepared with the composition (82.5-x) TeO2+4.5Bi2O3+11.5ZnO+1.5Nb2O5+x Er2O3 (x=0.1, 0.3, 0.5, 0.7, 1.0mol%) by melt-quenching method and their physical, spectroscopic properties were investigated. The experimental oscillator strengths (fexp) of individual absorption peaks are used to estimate the Judd–Ofelt intensity parameters (Ωλ, λ=2, 4, 6). Judd–Ofelt intensity parameters are used to calculate the spontaneous transition probabilities, radiative lifetimes and branching ratios for certain excited states of Er3+ ions. NIR emission and visible up-conversion luminescence were observed at room temperature for all glasses by exciting with 980nm laser radiation. The emission characteristics such as peak stimulated emission cross section, FWHM, figure of merit, optical gain cross sections and measured lifetimes have been obtained for the observed Er3+: 4I13/2→4I15/2 transition in the above glass composition for all the concentrations and are compared with that of the reported. Finally, NIR to visible energy conversion has been analyzed for all glasses excited at 980nm and suitable mechanism was proposed.

Judd Ofelt Analysis and Optical Properties of Rare Earth Doped Tellurite Glasses

In this work, the structural characteristic and photoluminescence properties were investigated in Eu\(^{3 + }\) ions-doped B\(_{2}\)O\(_{3}\)-TeO\(_{2}\) --ZnO-Na\(_{2}\)O glasses. These glasses were prepared by the melting method in air, after that thermal annealed 350\rc{}C, 450\rc{}C and 550\rc{}C for different times. The analysis results of structure on these glasses showed the formation of micro-crystals in host glass after thermal annealed process. The photoluminescence spectra of Eu\(^{3 + }\) ions in these samples were observed. The local vibration mode around Eu\(^{3 + }\) ions was investigated by the phonon side band associated with \(^{7}\)F\(_{0}\)- \(^{5}\)D\(_{2}\) transition of Eu\(^{3 + }\). Judd-Ofelt parameters have been evaluated from photoluminescence spectra and were to predict the luminescence intensity ratios of \(^{5}\)D\(_{0} \to ^{7}\)F\(_{J}\) (J=2, 4 and 6) to \(^{5}\)D\(_{0} \to ^{7}\)F\(_{1}\) transition. The obtained results have been used for calculating \(\Omega_{2}\), \(\Omega _{4}\), \(\Omega _{6}\) parameters by using Judd-Ofelt theory. These \(\Omega _{2}\), \(\Omega _{4}\), \(\Omega _{6}\) parameters allow to derive radiative properties of Eu\(^{3 + }\) ions in glass material such as transition probabilities, radiative lifetimes and peak stimulated emission cross-section for the \(^{5}\)D\(_{0} \to ^{7}\)F\(_{J}\) transitions.