A new theory explaining the intensity of
f
-
f
transitions and the crystal field using an approximation of a strong configuration interaction is proposed. The theory enables the anomalous influence ...of excited configurations with charge transfer on some multiplets of the
f
shell to be taken into account. With the help of this theory, a satisfactory description of the absorption transitions and luminescence branching ratios from
1
D
2
and
3
P
0
multiplets for the Pr
3+
ion in double molybdates has been achieved for the first time. For further validation the theory, was used to provide a description of Stark splitting of Pr
3+
— multiplets in elpasolites and determine the covalence parameters; these parameters were found to be in good agreement with values obtained by the other methods.
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.
•Judd-Ofelt theory accounting for thermal populations of Stark sub-levels.•Simple formulas for absorption strengths and radiative transition probabilities.•The contradiction between Tm3+ absorption and emission transition intensities is resolved.•Temperature dependence of luminescence lifetimes of the 3F4 Tm3+ manifold.•The case of Yb3+ ions featuring a small number of crystal-field sub-levels is considered.
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 %.
•Top-seeded solution growth of monoclinic KGd(WO4)2 crystals doped with Sm3+ ions.•Polarization-resolved study of absorption and stimulated-emission properties.•Transition intensities of Sm3+ ions calculated using a modified Judd-Ofelt theory.•Analysis of 4f - 4f excited-state absorption from the 4G5/2 level in the visible.•Red Sm:KGd(WO4)2 laser generated 37.8 mW at 649 nm with a laser threshold of 87 mW.
The purpose of this work is to determine the most adequate model for describing the experimental values of the intensities of the absorption bands of laser materials activated by trivalent erbium and ...thulium ions. Such materials are used as active media for lasers generating radiation in the infrared range of 1.5–2.8 μm. Calculation formulas are given for the oscillator strengths of absorption transitions in the Judd – Ofelt (J-O) model, the modified Judd – Ofelt (mJ-O) model, and in the approximation of an intermediate configurational interaction (ICI). To compare the adequacy of different models, the results of describing the experimental oscillator strengths of absorption transitions in six crystals activated by erbium ions and five crystals activated by thulium ions are considered. The most accurate description of ten of the eleven samples under consideration was obtained in the ICI model. In the calculations, we used the procedure for minimizing the error functional composed of the sum of the squared deviations of the calculated oscillator strengths from the corresponding experimental values. The criterion for choosing the best parameterization scheme is the minimum value of the root mean square deviations. A particularly noticeable improvement in the description is observed when using the ICI model for crystals activated by thulium ions. This is explained by the fact that multiplets with the same value of the total moment J combine into groups under the action of strong spin-orbit interaction. The action of excited configurations on any one multiplet is transmitted to all multiplets of the group. Thulium has a number of multiplets and consequently groups is much less than that of erbium. Therefore, the effect of excited configurations on thulium multiplets is more differentiated and easier to detect in the description. В качестве объекта исследования выбраны оксидные кристаллы, активированные трехвалентными ионами эрбия и тулия. Вероятностные характеристики поглощения и излучения таких кристаллов хорошо изучены экспериментально. Цель работы – установить наиболее адекватную модель для описания экспериментальных значений сил осцилляторов абсорбционных переходов. Основные расчетные формулы получены методами квантовой теории углового момента. Электрические дипольные f-f переходы, наблюдаемые в спектрах редкоземельных ионов, частично разрешены при учете влияния возбужденных конфигурация противоположной четности и конфигураций с переносом заряда. Для определения параметров интенсивности в различных схемах расчета используется процедура минимизации функционала ошибки, составленного из суммы квадратов отклонений вычисленных сил линий от соответствующих экспериментальных значений В ходе исследований выполнен сравнительный анализ адекватности модели Джадда – Офельта, модифицированной модели Джадда – Офельта и приближения промежуточного конфигурационного взаимодействия спектроскопических свойств активных лазерных сред, применяемых для генерации в инфракрасном диапазоне 1.5–2.8 мкм. Рассмотрены результаты описания 11 образцов по вышеперечисленным моделям. Критерием выбора наилучшей схемы параметризации служит минимальное значение среднеквадратичного отклонения. Установлено, что модифицированная модель Джадда – Офельта и приближения промежуточного конфигурационного взаимодействия обеспечивают непротиворечивое описание интенсивностных характеристик как поглощения, так и излучения лазерных материалов, активированных трехвалентными ионами эрбия и тулия.
A transparent “mixed” 7 at.% Er:(Lu,Sc)2O3 sesquioxide ceramic was fabricated by hot isostatic pressing of commercial sesquioxide powders at 1750 °C/200 MPa in argon atmosphere. It exhibited a cubic ...bixbyite-type structure (a = 10.198 Å), a mean grain size of 5.7 μm and high low-signal transmission of 79.1 % in the near-IR. The spectroscopic properties of Er3+ ions were studied. For the 4I11/2 → 4I13/2 transition, the stimulated-emission cross-section σSE is 1.30 × 10−20 cm2 at 2719 nm, the corresponding luminescence branching ratio B(JJ’) is 19.9 % and the radiative lifetime of the 4I11/2 state is 4.80 ms, as determined using a Judd-Ofelt theory accounting for intermediate configuration interaction. The crystal-field splitting of Er3+ multiplets was studied at 12 K. The ceramic exhibits a significant inhomogeneous broadening of spectral bands. An Er:(Lu,Sc)2O3 ceramic laser generated 342 mW at 2.71 and 2.85 μm with a high slope efficiency of 41.7 % (exceeding the Stokes limit) and a laser threshold of 125 mW.
•Transparent “mixed” 7 at.% Er:(Lu,Sc)2O3 sesquioxide ceramic.•Fabrication by hot isostatic pressing at 1750 °C / 200 MPa in argon atmosphere.•The stimulated-emission cross-section for Er3+ ions is 1.30 × 10-20 cm2 at 2719 nm.•The ceramic exhibits a significant inhomogeneous broadening of the spectral bands.•The ceramic laser generated 342 mW at 2.71&2.85 μm with a slope efficiency of 41.7 %.
We report on a comparative study of the spectroscopic properties and mid-infrared laser performance of five 5 at.% Er 3+ -doped fluorite-type crystals MF 2 , including parent compounds CaF 2 , SrF 2 ..., BaF 2 , and solid-solution (“mixed”) ones (Ca,Sr)F 2 and (Sr,Ba)F 2 . In the M = Ca → Sr → Ba series, the host matrix phonon energy decreases, the absorption and mid-infrared emission spectra of Er 3+ become narrower and more structured, and the luminescence lifetimes of the 4 I 11/2 and 4 I 13/2 Er 3+ manifolds increase. The Er 3+ transition probabilities were calculated using the Judd-Ofelt theory. In the “mixed” compounds, the Er 3+ ions tend to reside in the larger / heavier cation environment. The low-temperature (12 K) spectroscopy evidences the presence of a single type of clusters at this doping level; the crystal-field splitting for Er 3+ ions in clusters was determined. Continuous-wave low-threshold laser operation at ∼2.8 µm (the 4 I 11/2 → 4 I 13/2 transition) was achieved with all five Er 3+ :MF 2 crystals. The maximum achieved laser slope efficiency was 37.9% (Er 3+ :CaF 2 ), 23.5% (Er 3+ :SrF 2 ) and 17.2% (Er 3+ :BaF 2 ).
We report on the crystal growth, structure determination and the vibronic and spectroscopic properties of a novel red-emitting anisotropic crystal featured by a layered structure, the Eu3+-doped ...orthorhombic potassium yttrium double molybdate crystal, KY(MoO4)2. The transition probabilities of Eu3+ ions are determined within the Judd-Ofelt theory. The stimulated-emission cross-sections are calculated for the 5D0 → 7FJ transitions of Eu3+ with polarized light. The maximum σSE reaches 11.4 × 10−20 cm2 at 613.9 nm for E || c. The strong anisotropy of the spectroscopic properties of Eu3+ is attributed to the layered structure of KY(MoO4)2. The lifetime of the 5D0 state is 0.65 ms. Under UV excitation, Eu:KY(MoO4)2 provides red emission (CIE 1931 coordinates, x = 0.665 and y = 0.335) with almost unity color purity. Eu3+ ions are studied as structural probes, revealing a single type of site (C2 symmetry). The polarization-anisotropy of the purely magnetic-dipole 5D0 → 7F1 transition is discussed. Eu:KY(MoO4)2 is promising for red phosphors and deep-red lasers.
•Eu3+-doped orthorhombic potassium yttrium double molybdate, Eu:KY(MoO4)2.•Layered structure of Eu:KY(MoO4)2 determines anisotropy of its properties.•Rietveld refinement of the crystal structure and polarized Raman spectroscopy.•Judd-Ofelt modelling and calculation of stimulated-emission cross-sections.•The polarization-anisotropy of the purely magnetic-dipole Eu3+5D0 → 7F1 transition.
We report on the crystal growth, structure determination and the vibronic and spectroscopic properties of a novel red-emitting anisotropic crystal featured by a layered structure, the Eu3+-doped ...orthorhombic potassium yttrium double molybdate crystal, KY(MoO4)2. The transition probabilities of Eu3+ ions are determined within the Judd-Ofelt theory. The stimulated-emission cross-sections are calculated for the 5D0 → 7FJ transitions of Eu3+ with polarized light. The maximum σSE reaches 11.4 × 10−20 cm2 at 613.9 nm for E || c. The strong anisotropy of the spectroscopic properties of Eu3+ is attributed to the layered structure of KY(MoO4)2. The lifetime of the 5D0 state is 0.65 ms. Under UV excitation, Eu:KY(MoO4)2 provides red emission (CIE 1931 coordinates, x = 0.665 and y = 0.335) with almost unity color purity. Eu3+ ions are studied as structural probes, revealing a single type of site (C2 symmetry). The polarization-anisotropy of the purely magnetic-dipole 5D0 → 7F1 transition is discussed. Eu:KY(MoO4)2 is promising for red phosphors and deep-red lasers.
We report on a detailed revision of the spectroscopic properties of Er 3+ ions in the cubic sesquioxide host crystals R 2 O 3 (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 4 I 11/2 → 4 I 13/2 (at ∼2.8 µm) and 4 I 13/2 → 4 I 15/2 (at ∼1.6 µm) transitions of Er 3+ ions are determined and the luminescence dynamics from the 4 I 11/2 and 4 I 13/2 manifolds are studied at different temperatures. It is found that the luminescence lifetime of the 4 I 11/2 state strongly depends on the host-forming R 3+ cation even at low temperatures due to a non-negligible non-radiative multiphonon decay channel. Er:Y 2 O 3 exhibits the lowest phonon energies and consequently the longest 4 I 11/2 luminescence lifetimes. A disagreement between the absorption and emission probabilities for the 4 I 15/2 ↔ 4 I 11/2 transition of Er 3+ ions is observed at room temperature and explained considering the distribution of Er 3+ ions over two non-equivalent crystallographic sites, C 2 and C 3i .
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