Absorption of Dy3+ and Nd3+ ions in BaR 2F8 single crystals

The Dy³⁺ absorption and excitation spectra of BaY₂F₈ and BaYb₂F₈ single crystals are investigated in the ultraviolet, vacuum ultraviolet, and visible ranges at a temperature of 300 K. These crystals exhibit intense broad absorption bands due to the spin-allowed 4f-5d transitions in the range (56–78) × 10^?3 cm^?1 and less intense absorption bands that correspond to the spin-forbidden transitions in the range (50–56) × 10^?3 cm^?1. The Nd³⁺ absorption spectra of BaY₂F₈ single crystals are studied in the range (34–82) × 10^?3 cm^?1 at 300 K for different crystal orientations.     

Optical spectra and excited state relaxation dynamics of Sm<Superscript>3+</Superscript> in Gd<Subscript>2</Subscript>SiO<Subscript>5</Subscript> single crystal

Single crystals of gadolinium orthosilicate Gd₂SiO₅ containing 0.5 at% and 5 at% of Sm³⁺ were grown by the Czochralski method. Optical absorption spectra, luminescence spectra and luminescence decay curves were recorded for these systems at 10 K and at room temperature. Comparison of optical spectra recorded in polarized light revealed that the anisotropy of this optically biaxial host affects the intensity distribution within absorption and emission bands related to transitions between multiplets rather than the overall band intensity. It has been found that among four bands of luminescence related to the ⁴G_5/2→⁶H_J (J=5/2–11/2) transitions of Sm³⁺ in the visible and near infrared region the ⁴G_5/2 →⁶H_7/2 one has the highest intensity with a peak emission cross section of 3.54×10⁻²¹ cm² at 601 nm for light polarized parallel to the crystallographic axis c of the crystal. The luminescence decay curve recorded for Gd₂SiO₅:0.5 at% Sm³⁺ follows a single exponential time dependence with a lifetime 1.74 ms, in good agreement with the ⁴G_5/2 radiative lifetime τ _rad=1.78 ms calculated in the framework of Judd-Ofelt theory. Considerably faster and non-exponential luminescence decay recorded for Gd₂SiO₅:5 at% Sm³⁺ sample was fitted to that predicted by the Inokuti-Hirayama theory yielding the microparameter of Sm³⁺–Sm³⁺ energy transfer C _da=1.264×10⁻⁵² cm⁶×s⁻¹.     

Luminescence and defect studies of YAlO3:Dy3+, Sm3+ single crystals exposed to 100 MeV Si7+ ion beam

Ionoluminescence (IL) and photoluminescence (PL) spectra for different rare earth ions (Sm³⁺ and Dy³⁺) activated YAlO₃ single crystals have been induced with 100 MeV Si⁷⁺ ions with fluence of 7.81×10¹² ions cm^?2. Prominent IL and PL emission peaks in the range 550–725 nm in Sm³⁺ and 482–574 nm in Dy³⁺ were recorded. Variation of IL intensity in Dy³⁺ doped YAlO₃ single crystals was studied in the fluence range 7.81×10¹²–11.71×10¹² ions cm^?2. IL intensity is found to be high in lower ion fluences and it decreases with increase in ion fluence due to thermal quenching as a result of an increase in the sample temperature caused by ion beam irradiation. Thermoluminescence (TL) spectra were recorded for fluence of 5.2×10¹² ions cm^?2 on pure and doped crystals at a warming rate of 5 °C s^?1 at room temperature. Pure crystals show two glow peaks at 232 (Tg₁) and 328 °C (Tg₂). However, in Sm³⁺ doped crystals three glow peaks at 278 (Tg₁), 332 (Tg₂) and 384 °C (Tg₃) and two glow peaks at 278 (Tg₁) and 331 °C (Tg₂) in Dy³⁺ was recorded. The kinetic parameters (E, b s) were estimated using glow peak shape method. The decay of IL intensity was explained by excitation spike model.     

Optical spectroscopy and laser parameters of Zn2+/Er3+/Yb3+-tridoped LiNbO3 crystal

The Zn/Er/Yb:LiNbO₃ and Er/Yb:LiNbO₃ crystals were grown by the Czochralski technique. The laser characteristics of 1.54 μm emission were predicted based on the Judd–Ofelt theory, and the intensity parameters Ω_t (Ω₂=7.23×10^?20 cm², Ω₄=3.15×10^?20 cm² and Ω₆=1.43×10^?20 cm²) were obtained. The stimulated emission cross sections (σ_em) at 1.54 μm emission in Zn/Er/Yb:LiNbO₃ were calculated based on the McCumber theory and the Füchtbauer–Ladenburg theory. The gain cross section spectrum of Zn/Er/Yb:LiNbO₃ crystal was also investigated. Under 980 nm excitation, a lenghthening lifetime of 1.54 μm emission and an enhancement of green upconversion emission were observed for Zn/Er/Yb:LiNbO₃ crystal. The studies on the power pump dependence and the upconversion mechanism suggested that both green and red upconversion emissions were populated via the three-photon process, and Zn²⁺ ion tridoping increases the probability of cross relaxation process between the two neighboring Er³⁺ ions.     

Optical properties of Sm3+ and Dy3+ ions in Gd2MoB2O9 host lattice

Gd₂MoB₂O₉ doped with Sm³⁺ and Dy³⁺ were used for this study. The photoluminescence behaviors of Sm³⁺ and Dy³⁺ in this phosphor material were investigated by the excitation and emission spectra. The Sm³⁺-doped Gd₂MoB₂O₉ phosphor powders show a red luminescence, whereas the Dy³⁺-doped Gd₂MoB₂O₉ phosphor powders show a yellow luminescence. In addition, the optimum doping concentration and the time-resolved luminescence spectroscopy were also investigated.     

Intensities of f-f transitions in Pr3+ and Dy3+ in glasses in the near-IR spectral range

The absorption spectra of Pr³⁺ and Dy³⁺ ions in three glass matrices (SiO₂-P₂O₅-GeO₂, Al₂O₃-B₂O₃-SiO₂, and LiB₃O₅) are thoroughly studied in the near-IR spectral range (4600–14 300 cm^?1). The temperature dependences of the intensity, the width, and the location of the absorption bands observed are investigated for the first time. It is shown that the f-f transitions in the studied glasses are allowed by static odd distortions in the environment of the rare-earth ions and these distortions decrease with an increase in temperature. A comparative analysis of the absorption band parameters and their temperature behavior in different materials makes it possible to determine the differences in magnitudes, symmetries, and dispersions of the distortions in the nearest environment of rare-earth ions in different glasses.     

Optical amplification properties of Dy3+-doped Gd2SiO4, Lu2SiO5 and YAl3(BO3)4 single crystals

Comparative investigation of the optical amplification properties of dysprosium doped Gd₂SiO₅, Lu₂SiO₅ and YAl₃(BO₃)₄ single crystals was performed in a pump-and-probe experiment. High power laser pulses at 475 nm were used as the pump source in order to strongly populate the ⁴F_9/2 level of the Dy³⁺ ions due to ground state absorption. Low signal beam cw radiation at 574 nm was used as the probe beam to stimulate the emission associated with the ⁴F_9/2→⁶H_13/2 electronic transition of the Dy³⁺ ions. The process was modelled as a three levels system, and their populations were analysed and simulated in order to study the gain dynamics. Positive optical gain was observed and compared in these crystals. These results confirmed that among the systems studied the Dy³⁺-doped YAl₃(BO₃)₄ single crystal can be considered as a good candidate to develop an optical amplifier employing the ⁴F_9/2→⁶H_13/2 transition at around 574 nm which is the first step to consider as laser active media.     

Photon down-shifting by energy transfer from Sm3+ to Eu3+ ions in sol-gel SiO2-LaF3 nano-glass-ceramics for photovoltaics

95SiO₂?C5LaF₃ sol-gel derived nano-glass-ceramics single doped with Eu³⁺ or Sm³⁺ and codoped with both of them were successfully obtained. XRD measurements confirm the precipitation of LaF₃ nanocrystals after the ceramming process, with mean size ranging from 10 to 20?nm which increases with the thermal treatment temperature. The incorporation of rare-earth ions into precipitated LaF₃ nanocrystals was confirmed from luminescence spectra. Intense yellow-red emissions were detected under UV and blue light excitation in single and codoped samples. The effect of codoping with Eu³⁺ and Sm³⁺ ions and the energy transfer mechanism between them have been analyzed in order to increase the yellow-red emissions.     

Synthesis and photoluminescence properties of Dy3+, Sm3+ activated Sr5SiO4Cl6 phosphor

Dy³⁺ and Sm³⁺ doped Sr₅SiO₄Cl₆ phosphors were prepared by the modified solid state method and their luminescent properties were studied. From a powder X-ray diffraction (XRD) analysis the formation of Sr₅SiO₄Cl₆ was confirmed. In the photoluminescence emission spectra, the Sr₅SiO₄Cl₆:Dy³⁺ phosphors show efficient blue and yellow band emissions, which originates from the ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺ ion, respectively. Photoluminescence properties of Sm³⁺ doped Sr₅SiO₄Cl₆ phosphor exhibited characteristic orange-red emission coming from the intra-4f-shell ⁴G_5/2 →⁶H_J electron transitions.     

Electron paramagnetic resonance of Dy3+ in cubic ZnSe and Tm3+ in hexagonal CdS single crystals

Electron paramagnetic resonance has been observed for Dy³⁺ in ZnSe and Tm³⁺ in CdS. For Dy³⁺ doped ZnSe, an isotropic spectrum was observed having well resolved hyperfine lines due to ¹⁶¹Dy and ¹⁶³Dy. The g value obtained was 6.577 ± 0.002 and ¹⁶¹A was 191 ± 1 × 10⁴ cm^?1 and ¹⁶³A was 265 ± 3 × 10^?4 cm^?1. The agreement of the observed g value to g(τ₆) = 6.667 and the point-charge calculations suggest that Dy³⁺ occupies an interstitial (II) site with no local charge compensation. For Tm³⁺ doped in hexagonal CdS, an axial spectrum consistent with g_⊥ = 0, g_∥ = 10.722 ± 0.007, D = 2.57 GHz (crystal field splitting) and ¹⁶⁹A = 1207 ± 5 × 10^?4cm^?1. The large g_∥ value indicates that the Tm ion exits in the trivalent state. This is in reasonable agreement with previous reports of the non-Kramer's state of Tm³⁺.     

Dominant Cr3+ centers in LiNbO3 under hydrostatic pressure

Low-temperature luminescence spectra of stoichiometric Cr: LiNbO₃ and of congruent Cr, Mg: LiNbO₃ were studied. Cr³⁺ impurity ions preferentially occupy Li⁺ sites (Cr_Li) in the LiNbO₃ crystal lattice, while Cr³⁺ ions substituting for Nb⁵⁺ ions (Cr_Nb) occur in addition to Cr_Li centers in codoped Cr, Mg: LiNbO₃ crystals. Application of a high hydrostatic pressure leads to a transformation of (dominant in concentration) Cr³⁺ centers from low-to high-crystal-field centers. Due to a strong pressure-induced blue shift of the ⁴ T ₂ state resulting in crossing with the ² E state, the replacement of the broad band ⁴ T ₂ → ⁴ A ₂ emission by a narrow R-line emission ² E → ⁴ A ₂ occurs in the luminescence spectra of the samples. This effect of level crossing was observed for the dominant Cr _Li ³⁺ and Cr _Nb ³⁺ centers at pressures which correlated well with estimations based on the ⁴ T ₂-² E energy gap (230 and 1160 cm^?1) and on the rate of their pressure-induced change (14.35 and 11.4 cm^?1/kbar, respectively).     

Growth,spectral and laser properties of Nd3+:Na2La4(WO4)7 crystal

A Nd³⁺:Na₂La₄(WO₄)₇ crystal with dimensions of ? 17 × 30 mm³ was grown by the Czochralski method. The thermal expansion coefficients of Nd³⁺:Na₂La₄(WO₄)₇ crystal are 1.32 × 10^?5 K^?1 along c-axis and 1.23 × 10^?5 K^?1 along a-axis, respectively. The spectroscopic characteristics of Nd³⁺:Na₂La₄(WO₄)₇ crystal were investigated. The Judd–Ofelt theory was applied to calculate the spectral parameters. The absorption cross sections at 805 nm are 2.17 × 10^?20 cm² with a full width at half maximum (FWHM) of 15 nm for π-polarization, and 2.29 × 10^?20 cm² with a FWHM of 14 nm for σ-polarization. The emission cross sections are 3.19 × 10^?20 cm² for σ-polarization and 2.67 × 10^?20 cm² for π-polarization at 1,064 nm. The fluorescence quantum efficiency is 67 %. The quasi-cw laser of Nd³⁺:Na₂La₄(WO₄)₇ crystal was performed. The maximum output power is 80 mW. The slope efficiency is 7.12 %. The results suggest Nd³⁺:Na₂La₄(WO₄)₇ crystal as a promising laser crystal fit for laser diode pumping.     

Dipolar studies in CaF2 with Ce3+

Dielectric relaxation in CaF₂ doped with various amounts of Ce³⁺ (0·01 to 1·0 mol%) was measured. The value of the activation energy for orientation of the dipoles {Ce³⁺-F^? interstitial} was determined to be H = (0·46 ± 0·01) eV. The frequency factor was found to have the value τ_o = (5 ± 1) × 10^?15 sec, giving for the vibrational frequency of the interstitial the value ν_o = (5 ± 1) × 10¹³ sec^?1.The number of dipoles contributing to the dielectric loss peak was determined to be between 10¹⁷ and 8 × 10¹⁷ cm^?3 for the different doping amounts of Ce³⁺. Optical absorption measurements showed the existence of large aggregate bands. We could verify that there exists a second-order reaction of aggregation, which is responsible for the non-linearity found between optical absorption at 305 nm and the nominal concentration of Ce³⁺ in the samples. On the other hand, if we assume that the centers which contribute to optical absorption at 305 nm are those also responsible for the relaxation peak, we find that the number contributing to each process is not the same. We can define an interaction radius R as the minimum separation between two dipoles allowing them to contribute to the relaxation peak. From our experimental data R ? 3·8 × 10^?7 cm.     

Ca2SiO4:Dy3+材料的制备及其发光特性

采用高温固相法制备了Ca₂SiO₄:Dy³⁺发光材料.在365nm紫外光激发下,测得Ca₂SiO₄:Dy³⁺材料的发射光谱为一多峰宽谱,主峰分别位于486nm,575nm和665nm处;监测575nm发射峰,测得材料的激发光谱为一多峰宽谱,主峰分别位于331nm,361nm,371nm,397nm,435nm,461nm和478nm处.研究了Dy³⁺掺杂浓度对Ca₂SiO₄:Dy³⁺材料发射光谱及发光强度的影响,结果显示,随Dy³⁺浓度的增大,黄、蓝发射峰强度比(Y/B)逐渐增大,利用Judd-Ofelt理论解释了其原因;随Dy³⁺浓度的增大,Ca₂SiO₄:Dy³⁺材料发光强度先增大,在Dy³⁺浓度为4 mol%时到达峰值,而后减小,根据Dexter理论其浓度猝灭机理为电偶极-电偶极相互作用.研究了电荷补偿剂Li⁺,Na⁺和K⁺对Ca₂SiO₄:Dy³⁺材料发射光谱的影响,结果显示,不同电荷补偿剂下,随电荷补偿剂掺杂浓度的增大,Ca₂SiO₄:Dy³⁺材料发射光谱强度的演化趋势相同,即Ca₂SiO₄:Dy³⁺材料发射峰强度先增大后减小,但不同电荷补偿剂下,材料发射峰强度最大处对应的补偿剂浓度不同,对应Li⁺,Na⁺和K⁺时,浓度分别为4mol%,4mol%和3mol%. 关键词： 白光LED 2SiO₄:Dy³⁺')" href="#">Ca₂SiO₄:Dy³⁺ 发光特性 电荷补偿     

Optical Spectroscopy of Sm3+ and Dy3+ Doped ZnO Nanocrystals

Sm³⁺ and Dy³⁺ ions doped hexagonal wurtzite ZnO nanocrystals were fabricated by a sol-gel method. The obtained ZnO nanocrystals were characterized using the X-ray diffraction, transmission electron microscopy, ultraviolet-visible reflectance spectra, and low-temperature luminescence spectroscopy. Intense and well resolved emission lines for Sm³⁺ and Dy³⁺ ions can be achieved via an energy transfer process from ZnO host to the dopants. It was found that the host sensitized emissions were more efficient than that of direct excitation for Sm³⁺ and Dy³⁺ ions. Moreover, multiple sites of Sm³⁺ and Dy³⁺ ions in ZnO nanocrystals were identified based on the low-temperature photoluminescence spectra.     

Growth and spectroscopic studies of NaLa(MoO4)2:Tm3+ crystals: A new promising laser material

Single crystals of scheelite-like disordered double molybdate NaLa(MoO₄)₂ doped with thulium ions with dopant concentrations of 3.0 × 10¹⁹ and 1.2 × 10²⁰ cm^?3 are grown by the Czochralski method. Spectral and luminescent studies of crystals grown are performed in wavelength ranges of 800 nm (the transitions ³ H ₆?³ H ₄) and 2 μm (the transitions ³ H ₆?³ F ₄), including the measurements of the polarized absorption and luminescence spectra of these crystals and the decay kinetics of their excited states. A model that satisfactorily describes the decay kinetics of the luminescence from the ³ H ₄ level taking into account cross-relaxation interactions is proposed. The prospects for the use of these crystals as active media in two-micrometer solid-state lasers are discussed.     

Electron paramagnetic resonance of Dy3+ ions in lead thiogallate single crystals

The results of electron paramagnetic resonance (EPR) studies of Dy³⁺ ions in lead thiogallate PbGa₂S₄ single crystals have been presented. It has been shown that the ground state of these ions corresponds to the lowest Stark sublevel Γ₆ of the term ⁶ H _15/2. The spectra are well described by the axially symmetric spin Hamiltonian with the effective spin S = 1/2 with the factors g _‖ = 15.06 and g _⊥ = 2.47. The Dy³⁺ ions substitute Pb²⁺ ions in the crystal lattice of PbGa₂S₄. The observed hyperfine structure has allowed to unambiguously interpret the EPR spectra. The hyperfine interaction constants of two odd isotopes of dysprosium in lead thiogallate single crystals have been found to be A _‖ = 675 × 10^?4 cm^?1 and A _⊥ = 111 × 10^?4 cm^?1 for ¹⁶³Dy and A _‖ = 472 × 10^?4 cm^?1 and A _⊥ = 77 × 10^?4 cm^?1 for ¹⁶¹Dy.     

The effect of charge compensation by means of Na+ ions on the luminescence behavior of Sm3+-doped CaAl4O7 phosphor

Results of structural and spectroscopic measurements of Sm³⁺ doped calcium aluminates: Ca_1?xSm_xAl₄O₇ and Ca_1?2xSm_xNa_xAl₄O₇ (x=0.0005, 0.002, 0.01, 0.02, 0.03, 0.05) obtained by the modified Pechini method are presented. All samples yield intense orange–red emission under violet excitation (404.5 nm). Narrow bands corresponding to characteristic f–f intraconfigurational transition of Sm³⁺ in excitation and emission spectra were observed. The influences of the concentration of Sm³⁺ as well as charge compensation by co-doping with Na⁺ ions on the luminescent properties of the phosphor were investigated. Detailed analysis of the emission spectra of Sm³⁺ doped and Sm³⁺,Na⁺ co-doped CaAl₄O₇ powders proved that activator ions substitute Ca²⁺ in the host. Co-doping with Na⁺ ions enhanced greatly the intensity of the luminescence. Concentration dependencies of the intensity of luminescence and its decay kinetics proved the emission quenching at higher dopant contents due to cross-relaxation processes between Sm³⁺ ions. Fitting of the ⁴G_5/2 state fluorescence decay to the Inokuti–Hirayama model indicated dipole–dipole interaction as the dominant mechanism of the cross-relaxation processes.     

Optical absorption and fluorescence studies of Dy3+-doped lead telluroborate glasses

Lead telluroborate (PTBDy) glasses doped with different Dy³⁺ ion concentrations were prepared by melt quenching technique and investigated through optical absorption, fluorescence and decay measurements. The Judd–Ofelt intensity parameters (Ω_λ) are obtained by a least square fit analysis. The small root mean square deviation of ±0.34×10^?6 shows a good fit between the experimental and calculated oscillator strengths. The radiative properties of the ⁴F_9/2→⁶H_13/2 emission transition of PTBDy10 glass are determined and compared to the other reported glasses. The variation of decay time of the ⁴F_9/2 emission state is attributed to the interaction among the excited Dy³⁺ ions at higher concentration. The PTBDy10 glass is found to be a suitable candidate for solid state laser materials to produce intense yellow (576 nm) luminescence through the ⁴F_9/2→⁶H_13/2 transition.     

Concentration quenched luminescence and energy transfer analysis of Nd3+ ion doped Ba-Al-metaphosphate laser glasses

This paper reports the dopant ion (Nd³⁺) concentration effects on its luminescence properties in a new glass system based on barium-alumino-metaphosphates. Amongst the studied concentrations range of 0.276–13.31×10²⁰ ions/cm³, the glass with 2.879×10²⁰ ions/cm³ (1 mol%) Nd³⁺ concentration shows intense NIR emission from ⁴F_3/2 excited state, followed by a decrease in emission intensity for further increase in Nd³⁺ ion concentration. The observed luminescence quenching is ascribed to Nd³⁺ self-quenching through the donor-donor migration assisted cross-relaxation mechanism. The microscopic energy transfer parameters for donor-acceptor energy transfer, C _DA, and donor-donor energy migration, C _DD, have been obtained from the theoretical fittings to experimental decay curves and the spectral overlap model respectively. The C _DD parameters (×10^?39 cm⁶/sec) are found to be about three orders greater than that of C _DA (×10^?42 cm⁶/sec) for Nd³⁺ self-quenching in this host, demonstrating that the excitation energy migration among donors is due to the hopping mechanism. The energy transfer micoparameters obtained in the present study are comparable to the values reported for commercially available laser glasses LHG-8 and Q-98.