Modified Judd-Ofelt Theory Research Articles

Polarized spectroscopy of Sm3+ ions in monoclinic KGd(WO4)2 crystals for lasers emitting in the red

Single-crystals of potassium gadolinium double tungstate KGd(WO4)2 doped with Sm3+ ions up to 20 at.% were grown from the flux using K2W2O7 as a solvent and a detailed polarization-resolved spectroscopic study of Sm3+ ions was performed with the goal of developing novel materials emitting in the visible spectral range. Polarized absorption spectra were measured and 4f-4f transition intensities of Sm3+ ions were calculated using a modified Judd-Ofelt theory yielding the intensity parameters of Ω2 = 8.027, Ω4 = 7.210 and Ω6 = 2.322 [10−20 cm2] and α = −0.017 [10−4 cm]. Polarized stimulated-emission properties of Sm3+ ions were studied. For the 4G5/2 → 6H9/2 transition in the red, the maximum σSE is 0.55 × 10−20 cm2 at 649.0 nm for light polarization E || Np (luminescence branching ratio: 40.2 %). The radiative lifetime of the 4G5/2 state is 734 μs. The luminescence dynamics from this manifold was analyzed using the Inokuti-Hirayama model. The possible role of 4f – 4f excited-state absorption from the 4G5/2 level in preventing laser operation in the orange and deep red is analyzed. A 0.8 at.% Sm:KGd(WO4)2 laser generated an output power of 37.8 mW at 649 nm, with a laser threshold of 87 mW and a slope efficiency of 17.6 %.

Engineering atomic size mismatch in Pr3+, La3+ codoped Lu3Al5O12 garnet single crystals for tailored structure and functional properties

This study provided the first in-depth investigation of the effects of large dopant incompatibility (Pr3+ and La3+ ions) on the small host lattice element (Lu3+) in Lu3Al5O12 (LuAG) single crystal. The growth of such complex crystals from the melt presented many challenges. By engineering the ionic radius ratio of RE- and M-site cations, a single-crystal phase stabilized by configurational entropy was achieved. This investigation elucidated the crystallization behavior of configurationally disordered rare-earth aluminum garnet oxide (Lu1−x−yPrxLay)3Al5O12 from the melt and characterized its functional properties, including microstructural, optical, photoluminescence, and scintillation properties, between 5 and 300 K. Relaxation of the imposed strain energy led to local perturbations and destabilization of the garnet structure. Multielemental EDS mapping, micro-Raman spectroscopy, and thermoluminescence revealed the mechanism by which atomic size mismatch drove a smooth transition from the garnet to the perovskite phase in high entropy garnets. The optical, photoluminescence, and scintillation measurements provided fundamental insights into property changes driven by incompatibility doping. Standard and modified Judd-Ofelt theory analysis of absorption spectra determined the phenomenological Judd-Ofelt parameters Ωλ and radiative lifetimes. Atomic size mismatch engineering offers a promising approach to overcoming the limitations of conventional eutectic synthesis methods.

On the temperature dependence of transition intensities of rare-earth ions: A modified Judd-Ofelt theory

We report on a modification of the Judd-Ofelt theory accounting for thermal populations of Stark sub-levels of the multiplets involved in transitions in absorption and emission. The calculations require the data on the crystal-field splitting, the irreducible representations of Stark sub-levels and the selection rules for electric-dipole transitions. Simple formulas for absorption oscillator strengths and probabilities of radiative spontaneous transitions are obtained. The application of the proposed model allowed us to remove the contradiction between the transition intensities in absorption and emission (3H6 ↔ 3F4) for Tm3+-doped crystals. It was also used to explain the experimental temperature dependences of luminescence lifetimes of the 3F4 Tm3+ manifold in two widely used laser crystals, LiYF4 and Y3Al5O12. The case of Yb3+ ions featuring a small number of crystal-field sub-levels is also considered.

Stimulated-emission cross-sections of trivalent erbium ions in the cubic sesquioxides Y2O3, Lu2O3, and Sc2O3

We report on a detailed revision of the spectroscopic properties of Er3+ ions in the cubic sesquioxide host crystals R2O3 (R = Y, Lu and Sc). The 4f-4f transition probabilities are calculated by applying a modified Judd-Ofelt theory accounting for configuration interaction based on the measured absorption spectra. The stimulated-emission cross-sections for the 4I11/2 → 4I13/2 (at ∼2.8 µm) and 4I13/2 → 4I15/2 (at ∼1.6 µm) transitions of Er3+ ions are determined and the luminescence dynamics from the 4I11/2 and 4I13/2 manifolds are studied at different temperatures. It is found that the luminescence lifetime of the 4I11/2 state strongly depends on the host-forming R3+ cation even at low temperatures due to a non-negligible non-radiative multiphonon decay channel. Er:Y2O3 exhibits the lowest phonon energies and consequently the longest 4I11/2 luminescence lifetimes. A disagreement between the absorption and emission probabilities for the 4I15/2 ↔ 4I11/2 transition of Er3+ ions is observed at room temperature and explained considering the distribution of Er3+ ions over two non-equivalent crystallographic sites, C2 and C3i.

Polarized spectroscopy of Sm3+ ions in monoclinic KGd(WO4)2 crystals

We report on a polarization-resolved spectroscopic study of Sm3+-doped monoclinic KGd(WO4)2 crystals. The transition probabilities for Sm3+ ions were calculated using a modified Judd-Ofelt theory. For the 4G5/2 → 6H9/2 transition in the red spectral range, the stimulated-emission cross-section is 5.59×10-21 cm² at 649.0 nm (for light polarization E || Np) and the luminescence lifetime of the 4G5/2 state is 719 μs (0.4 at.% Sm3+-doping). Sm:KGd(WO4)2 is promising for orange and red lasers.

Spectral analysis and emission properties of 3P0 and 1D2 levels in Pr:ZBLAN fiber

In order to investigate the optical properties of Pr:ZBLAN fibers, the standard and modified Judd-Ofelt theory are introduced to calculate the spectral parameters. The experimental and measured dipole line strength is obtained to derive the intensity parameters. Also, the emission properties are comprehensively estimated. For the 3P0 energy level, the generated transitions are represented in detail, and the quantum efficiency is obtained by measuring the fluorescence lifetime. The emission cross-section spectrum is presented as well. Moreover, we have further explored the emission properties of 1D2 level and analyzed the main transitions in the emission cross-section spectrum, which provides a solid theoretical foundation for the development of new mechanisms lasing in the Pr:ZBLAN fiber.

Tm,Ho:Ca(Gd,Lu)AlO4 crystals: Crystal growth, structure refinement and Judd-Ofelt analysis

“Mixed” calcium rare-earth aluminate laser host crystals Ca(Gd,Lu)AlO4 (CALGLO) with up to 10.8 at.% Lu codoped with Tm3+ and Ho3+ ions are grown by the Czochralski method along the [001] direction. The segregation of rare-earth ions is studied. The crystal structure is refined by the Rietveld method. Tm,Ho:Ca(Gd,Lu)AlO4 crystallizes in the tetragonal system (sp. gr. I4/mmm) exhibiting a K2NiF4 type structure. The lattice constants are a = 3.6585(6) Å and c = 11.9660(9) Å for a crystal with a composition of CaGd0.8947Lu0.0551Tm0.0448Ho0.0054AlO4. The stability of Ca(Gd,Lu)AlO4 solid-solutions is discussed. The polarized Raman spectra are measured, revealing a most intense mode at 311 cm−1 and a maximum phonon frequency of ∼650 cm−1. The polarized absorption spectra are measured. The transition intensities for the Ho3+ ion are analyzed using the modified Judd-Ofelt theory accounting for configuration interaction.

Tm3+-doped calcium lithium tantalum gallium garnet (Tm:CLTGG): novel laser crystal

We report on the development of a novel laser crystal with broadband emission properties at ∼2 µm – a Tm3+,Li+-codoped calcium tantalum gallium garnet (Tm:CLTGG). The crystal is grown by the Czochralski method. Its structure (cubic, sp. gr. I a 3 ¯ d , a = 12.5158(0) Å) is refined by the Rietveld method. Tm:CLTGG exhibits a relatively high thermal conductivity of 4.33 Wm-1K-1. Raman spectroscopy confirms a weak concentration of vacancies due to the charge compensation provided by Li+ codoping. The transition probabilities of Tm3+ ions are determined using the modified Judd-Ofelt theory yielding the intensity parameters Ω2 = 5.185, Ω4 = 0.650, Ω6 = 1.068 [10−20 cm2] and α = 0.171 [10−4 cm]. The crystal-field splitting of the Tm3+ multiplets is revealed at 10 K. The first diode-pumped Tm:CLTGG laser generates 1.08 W at ∼2 µm with a slope efficiency of 23.8%. The Tm3+ ions in CLTGG exhibit significant inhomogeneous spectral broadening due to the structure disorder (a random distribution of Ta5+ and Ga3+ cations over octahedral and tetrahedral lattice sites) leading to smooth and broad gain profiles (bandwidth: 130 nm) extending well above 2 µm and rendering Tm:CLTGG suitable for femtosecond pulse generation.

Growth, spectroscopy and laser operation of monoclinic Nd:CsGd(MoO4)2 crystal with a layered structure

We report on the growth, structure, polarized spectroscopy and first laser operation of a double molybdate compound featuring a layered structure – the monoclinic Nd:CsGd(MoO4)2. Single-crystals of 3 at.% Nd:CsGd(MoO4)2 are grown from the flux using cesium trimolybdate (Cs2Mo3O10) as a solvent. They crystallize in the monoclinic system (sp. gr. P2/c) with lattice constants a = 9.5239(4) Å, b = 5.0752(5) Å, c = 8.0580(7) Å and β = 91.157(9)°. Nd:CsGd(MoO4)2 exhibits a perfect cleavage along the (100) plane. Polarized absorption and luminescence spectra of the Nd3+ dopant ion are measured. The maximum stimulated-emission cross-section is 29.0 × 10−20 cm2 at 1065.9 nm for light polarization E ||b. The luminescence lifetime is 145 μs. The transition probabilities are determined using the modified Judd-Ofelt theory yielding the intensity parameters Ω2 = 26.736, Ω4 = 12.736 and Ω6 = 17.771 [10−20 cm2] and α = 0.122 [10−4 cm]. Continuous-wave laser operation is achieved in cleaved single-crystal plates of Nd:CsGd(MoO4)2 yielding a maximum output power of 0.54 W at 1066 nm with a laser threshold of 70 mW, a slope efficiency η of 60.4% and a linearly polarized laser output (E ||b).

Spectroscopy and diode-pumped laser operation of transparent Tm:Lu3Al5O12 ceramics produced by solid-state sintering.

A transparent Tm:Lu3Al5O12 ceramic is fabricated by solid-state reactive sintering at 1830 °C for 30 h using commercial α-Al2O3 and Lu2O3/Tm2O3 powders and sintering aids - MgO and TEOS. The ceramic belongs to the cubic system and exhibits a close-packed structure (mean grain size: 21 µm). The in-line transmission at ∼1 µm is 82.6%, close to the theoretical limit. The spectroscopic properties of the ceramic are studied in detail. The maximum stimulated-emission cross-section is 2.37×10-21 cm2 at 1749nm and the radiative lifetime of the 3F4 state is about 10 ms. The modified Judd-Ofelt theory accounting for configuration interaction is applied to determine the transition probabilities of Tm3+, yielding the intensity parameters Ω2 = 2.507, Ω4 = 1.236, Ω6 = 1.340 [10-20 cm2] and α = 0.196×10-4 cm. The effect of excited configurations on lower-lying interconnected states with the same J quantum number is discussed. First laser operation is achieved under diode-pumping at 792 nm. A 4 at.% Tm:Lu3Al5O12 ceramic laser generated 3.12 W at 2022-2035nm with a slope efficiency of 60.2%. The ceramic is promising for multi-watt lasers at >2 µm.

Rich reddish-orange emitting PBTNAPr glasses for laser applications

Lead borate oxyfluoride glasses containing different amounts of PrF3 with composition PbO–B2O3–TeO2–NaF–AlF3-PrF3 were prepared and characterized for visible and fiber lasers. The amorphous phase and compositional analysis were carried out through powder X-ray diffraction and Fourier transform infrared spectra, respectively. Using the room temperature optical absorption spectra, the spectroscopic properties were determined applying the modified Judd-Ofelt theory. The photoluminescence excitation spectral studies obtained by controlling the emission through Pr3+: 1D2 → 3H4 (604 nm) transition shows prominent excitation band positioned at ~448 nm (3H4 → 3P2). Upon 448 nm excitation, the studied glasses exhibit an intense emission through 1D2 → 3H4 (604 nm) transition along with feeble emissions from 3P1 and 3P0 metastable levels to the inner energy levels. The emission spectra show a shift towards longer wavelengths (called the red-shift) with increase of PrF3 content. The luminescence decay time of 1D2 emission level was found decreased with increase of PrF3 content. The quenching of decay time was assigned to the transfer of energy among the excited Pr3+ ions at relatively higher PrF3 contents. The experimental results show that the studied glasses with 0.1 mol% of PrF3 could be the suitable candidate to design rich reddish-orange emitting lasers.

Growth, spectroscopy and first laser operation of monoclinic Ho3+:MgWO4 crystal

A monoclinic 0.86 at.% Ho3+:MgWO4 crystal is grown by the Top-Seeded-Solution Growth method. Its spectroscopic properties are studied with polarized light for E || a, b, c. The Ho3+ ion transition probabilities are determined within the modified Judd-Ofelt theory (mJ-O) accounting for the configuration interaction. The intensity parameters are Ω2 = 21.09, Ω4 = 4.42, Ω6 = 2.28 [10–20 cm2] and α = 0.053 [10-4 cm]. The calculated radiative lifetime of the 5I7 state is 6.18 ms. The Stark splitting of the 5I7 and 5I8 multiplets is determined with low-temperature spectroscopy. The absorption, stimulated-emission (SE) and gain cross-sections for the 5I8 ↔ 5I7 transition are derived. Ho3+:MgWO4 features a large Stark splitting of the ground-state (380 cm-1), high maximum σSE of 1.82 × 10–20 cm2 at 2.083 μm, broad gain spectra and high luminescence quantum yield making it suitable for efficient continuous-wave and mode-locked lasers at ∼2.1 μm. First laser operation of Ho3+:MgWO4 crystal is demonstrated at 2.104 μm reaching a slope efficiency of 72%.

Environmentally friendly growth of fluoride crystal LiYF4: Pr3+ with broadband near-infrared emission from 1D2 manifolds

In this paper, an environmentally friendly Bridgman-Stockbarger technique was used to growth a fluoride single crystal LiYF4: Pr3+ (YLF: Pr3+). Polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves were measured at room temperature. A broad emission extending from 0.75 to 1.09 μm was recorded in YLF: Pr3+ by 594 nm excitation. Detailed polarized spectral analyses related to the 1D2 multiplet were carried out based on the modified Judd-Ofelt theory. The relationship between the calculated spectral parameters and the fluorescence spectra for the 1D2 multiplet of Pr3+ ions was discussed. The results imply that the YLF: Pr3+ crystal may be a potential tunable infrared laser gain medium with the 1D2 as an upper level.

Crystal growth, spectral properties and Judd-Ofelt analysis of Pr3+:LaMgAl11O19

Pr3+-doped LaMgAl11O19 (LMA) crystals have been successfully grown by the Czochralski method with different concentrations ranging from 0.5 to 10.0 mol%. Crystalline quality and the phonon energy were determined by X-ray diffraction and Raman measurements. Spectroscopic parameters based on absorption spectra were systematically calculated using the modified Judd-Ofelt theory. The fluorescence results indicate a large dependence on the factor of doping concentration. The 3P0→3F2 transition red laser channel has the largest emission cross section at 10.7 × 10−20 cm2 for 5.0 mol% Pr:LMA. The fluorescence lifetime of the 3P0 energy level is determined to be 32.6 μs at room temperature with a quantum efficiency of 82.9% for a 5.0 mol% Pr3+-doped sample. The overall spectral properties confirm that Pr:LMA is a promising candidate for visible laser operation.

Effect of Configuration Interaction of Rare-Earth Ion States on the Intensity of Intermultiplet Transitions

We present the analysis of wave functions and the effect of configuration interaction on the intensity of absorption bands for Pr3+, Tm3+, and Er3+ ions. It is shown that due to the strong spin–orbit interaction the wave functions of rare-earth ions are multicomponent superpositions of ″pure″ 2S+1LJ multiplets with different values of S and L and the same values of the angular momentum J. For this reason, the effect of configurational interaction depends not only on the energy gap up to excited configurations, but also on the presence of high-energy 2S+1LJ components. The presence of such components yields a strong influence on the configuration interaction even at the deep layers. Another consequence of the multicomponent composition of the wave functions is the formation of groups of strongly interrelated states. When the configuration interaction is not fully taken into account, the error in describing the oscillator strengths is distributed among all the states of the group, and the low overall accuracy of the description is not perceived as a contradiction to the theory. To confirm the proposed assumptions, the oscillator strengths of the absorption transitions of laser materials activated by Pr3+, Tm3+, and Er3+ ions are described using the modified Judd–Ofelt theory.

Influence of Bi3+ ions on the amplification of 1.3 μm emission of Pr3+ ions in lead silicate glasses for the applications in second telecom window communications

The primary objective of this study is to characterize 1G4 → 3H5 (1.3μm, which is highly important in telecommunications) and also 3P0 → 3F2 (red emission) spectral lines of Pr3+ ions in lead silicate glasses sensitized with bismuth ions. The intensity of these spectral lines exhibited large amplification (nearly four times) due to co-doping with Bi3+ ions with fixed concentration of Pr3+ ions. Several radiative parameters, e.g., transition probabilities (Aij), branching ratios (β), radiative life times (τ) and quantum efficiencies (η) of these spectral lines were evaluated using modified Judd-Ofelt theory. These parameters exhibited the maximal values when the glasses were codoped with the optimal concentration of Bi2O3 (5.0mol%). The increasing population of 3P0 and 1G4 levels of Pr3+ ions (with the gradual increase of Bi2O3 concentration up to 5.0mol%) that caused the amplification of above mentioned emissions occurred: (i) due to the energy transfer from 3P1→1S0 emission transition of Bi3+ ions and (ii) due to the increasing presence of Bi3+ ions in octahedral positions that are predicted to induce structural defects in the glass network. The quantitative analysis of these results together with the kinetic rate equations suggested that the Pr3+ ions doped lead silicate glasses mixed with (about 5.0mol%) Bi2O3 are highly efficient in producing intense 1.3μm (1G4 → 3H5) narrow emission. Hence, it is concluded that the optical fibers drawn from the glasses of such compositions are highly useful for the applications in the second telecom window.

Judd–Ofelt analysis of Pr3+ ions in Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 host matrices

The spectroscopic properties of Pr3+ doped Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 host matrices have been investigated using optical absorption and emission spectra. The oscillator strengths of observed bands of Pr3+ ions and Judd–Ofelt intensity parameters were calculated by including and excluding the hypersensitive 3H4→3P2 transition using standard and modified Judd–Ofelt (JO) theory. In both the host matrices the JO parameters follow the same trend as Ω6>Ω2>Ω4. The JO intensity parameters obtained by using the Modified JO theory was used to compute the radiative properties such as radiative transition probability (AR), branching ratio (βR) and radiative lifetime (τR) for the observed fluorescence bands. The photoluminescence spectrum of Pr3+ doped Sr1.5Ca0.5SiO4 upon 444nm excitation shows three emission peaks at 489, 608 and 733nm corresponding to the transitions 3P0→3H4, 3H6 and 3F4 respectively. But in the case of Sr0.5Ca0.5TiO3 host matrix we observed an emission peak at 611nm corresponding to the 1D2→3H4 transition at λex=336nm. The experimental branching ratio (βexp) obtained from the fluorescence spectra was compared with the calculated values. The non radiative relaxation rate was calculated from the experimental (τexp) and predicted (τR) lifetimes. Stimulated emission cross section (σe), gain bandwidth (σe×Δλeff) and optical gain (σe×τR) for 0.5wt% Pr3+ doped Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 phosphor samples were also calculated and their high value suggests its candidature as a good optical material.

Spectroscopy and Calculations for f-f Transitions of Tb3+ Ions in KY3F10 Nanocrystal.

A modified Judd-Ofelt theory is used in this paper to treat the electric dipole transitions within the 4f8 configuration of Tb3+ by considering the main perturbing components. Through the energy-level calculation and the strandard tensorial analysis, the explicit distances between the 4f7 5d configuration and the 5D4 state and other lower 4f8 energy levels are determined. The rare-earth ion Tb3+ substituted at Y3+ sites in KY3F10 has the site symmetry of C4v. The standard Judd-Ofelt parameters A2(10), A2(30), A4(30), A4(50), A6(50), A4(54) and A6(54) are included in the calculation together with odd-λ parameters A1(10), A3(30), A5(50) and A5(54). The fluorescence branching ratios originating from 5D4 are calculated. Compared with the experimental measurements, the modified model yields better results than the standard Judd-Ofelt theory.

Cooperative up-conversion in Eu3 +,Yb3 +-doped SiO2–PbO–PbF2–CdF2 oxyfluoride glass

Novel oxyfluoride glass doped with YbF3 and Eu2O3 is synthesized in the SiO2–PbO–PbF2–CdF2 system by melt-quenching technique. Its physical properties, as well as the optical absorption of Eu3+ and Yb3+ ions are studied. Spectroscopic properties of Eu3+ ions are modeled within modified Judd–Ofelt theory, yielding absorption oscillator strength, luminescence branching ratios and radiative lifetime of 5D0 state. Intrinsic emission of Eu3+ ions under direct excitation in the UV, as well as up-conversion luminescence under near-IR excitation via cooperative energy transfer, 2Yb3+→Eu3+, are studied. In the latter case, the glass provides intense reddish-orange emission with CIE coordinates x=0.636, y=0.363. The asymmetry parameter R for Eu3+ emission in the studied glass is about 8. The efficiency of this transfer mechanism is estimated from shortening of 2F5/2(Yb3+) lifetime to be 10±1%.

Application of modified Judd–Ofelt theory and the evaluation of radiative properties of Pr3 +-doped lead telluroborate glasses for laser applications

Praseodymium doped lead telluroborate (PTBPr) glasses were prepared by conventional melt quenching method. The absorption spectra have been analyzed to evaluate the intensity parameters applying the standard and the modified Judd–Ofelt theories. The emission spectra under 3P2 level excitation (λex=447nm) were investigated to estimate the laser characteristic parameters. These emission measurements together with Judd–Ofelt intensity parameters (Ωλ=2,4,6) have been used to calculate the radiative transition probabilities, fluorescence branching ratios and radiative lifetimes of the transitions from 3P0 and 1D2 levels to their lower lying levels. The quenching of fluorescence intensity and experimental lifetime with the increase of Pr3+ concentration and the shift of 1D2→3H4 emission peak towards longer wavelengths was discussed. The non-radiative losses due to multiphonon and energy transfer relaxations were also explained. The Commission Internationale de I'Eclairage (CIE) coordinates, color purity and optical band gap energy values were evaluated. Some of the basic laser characteristics such as stimulated emission cross-section, optical and bandwidth gain parameters and fluorescence quantum efficiency were also reported.