Temperature-dependent segregation of Pr3+ impurity ions in Y2SiO5:Pr3+ and YPO4:Pr3+ nanocrystals

Stationary and time-resolved spectroscopic methods are used to show that the impurity ions in Y₂SiO₅:Pr³⁺ and YPO₄:Pr³⁺ nanocrystals are distributed nonuniformly. This nonuniform distribution is found to be caused by the temperature-dependent segregation of Pr³⁺ ions near the surface of a nanocrystal. The motion of the activator ions from the bulk of a nanocrystal to the near-surface layer is traced when the activator concentration and the heat-treatment parameters are varied over wide ranges, and the main parameters of this effect (impurity redistribution intensity and time, diffusion coefficient) are estimated.     

Luminescence of Ca(NbO3)2:Pr3+: Pr3+ and self-trapped exciton emission

Photoluminescence and time resolved photoluminescence spectra of Ca(NbO₃)₂ doped with Pr³⁺, excited under 37,000 cm^?1 (270 nm), obtained at high hydrostatic pressure up to 20 kbar applied in a sapphire anvil cells, are presented. At ambient conditions, the emission spectrum obtained in the time interval 0–1 μs is dominated by spin allowed transitions from the ³P₀ state. The luminescence related to transitions from ¹D₂, characterized by a decay time equal to 33 μs, is observed when one excites directly the Pr³⁺ ion with 30,770 cm^?1 (325 nm) wavelength. The introduction of Pr³⁺ impurities in Ca(NbO₃)₂ does not quench the self-trapped exciton (STE) luminescence. This luminescence, peaking at 20,000 cm^?1 (500 nm), having a decay time of 61 ± 1 μs, still occurs when the crystal is excited with a wavelength of 37,000 cm^?1 (270 nm) or shorter. Under such excitation a fraction of the STE luminescence is reabsorbed by Pr³⁺ ions; in this case the emission lifetime of the ¹D₂ → ³H₄ transition of Pr³⁺ is 64 ± 3 μs. This effect is stable also at high pressure.     

Laser excitation of Pr3+ sites in ThCl4:Pr3+

Use of site selection spectroscopic techniques combined with low temperature absorption spectral studies has enabled the identification and characterization of ten optically important charge-compensated crystallographic sites for Pr³⁺ in the β-ThCl₄:Pr³⁺ system. Fluorescence decay time measurements, variation of site distribution with dopant concentration and fluorescence spectra were used to characterize the sites. Distant charge compensation is found to be one of the dominant modes of charge compensation of Pr³⁺ in ThCl₄, and its predominance over other sites increases as Pr³⁺ concentration decreases. The sinusoidal distortion of the crystal field symmetry around Pr³⁺ in the incommensurate phase of β-ThCl₄ is believed to be mainly responsible for the splitting and continuous shift in fluorescence spectral lines which occur when ³P₀→³F₂ fluorescence scans are made with excitation at different points on the ³P₀←³H₄ absorption line belonging to different sites.     

GdBO3：Pr3+，Yb3+中Pr3+到Yb3+的能量传递及发光性质

采用高温固相法制备了一系列单掺或双掺Pr3+和Yb3+的GdBO3材料,分别测试分析了材料的物相结构和发光性质。在446 nm蓝光( Pr3+：3 H4→3 P2)激发下,检测到Yb3+的近红外特征发射,表明样品中存在Pr3+到Yb3+的能量传递。 Pr3+的掺杂浓度一定时,样品的发光会随着Yb3+掺杂浓度的改变而发生变化。通过对比不同掺杂情况下Pr3+：3 P0能级的衰减曲线,发现随着Yb3+的掺杂浓度的增加,该能级的荧光寿命不断缩短;同时利用不同条件下的衰减特性计算得出不同 Yb3+掺杂浓度样品的能量传递效率。用 Inokuti-Hirayama模型分析表明Pr3+-Yb3+能量传递类型为偶极子-偶极子相互作用。     

偏硅酸钙中Pr3+的4f5d态的光谱特性及Pr3+→Gd3+的能量传递

合成了高效发射UV光的CaSiO3:Pr^3 新型荧光体，研究了室温下Pr^3 的4f5d态的发射和激发光谱，Pr^3 的4f5d态的最低子能级向4f^2组态的^3H4，^3H6和^1G4能级跃迁产生UV发射，并不伴随有4f-4f能级跃迁的可见光发射。Pr^3 的浓度猝灭是由于辐射和无辐射能量传递造成的，同时，在CaSiO3中，存在Pr^3 →Cd^3 的能量传递，探讨了其能量传递特性。     

Luminescence Spectroscopy and Decay Kinetics of Pr3+ Ions in K3LuSi2O7:Pr3+

Physics of the Solid State - The luminescent characteristics of K3LuSi2O7:Pr3+ (1%), which is a promising optical material for the use as a scintillator, have been studied using a set of...     

Compact Two-Color Pr3+-Doped ZBLAN Fiber Lasers

Two-color laser simultaneous oscillation in compact trivalent praseodymium ion (Pr³⁺)-doped ZrF₄-BaF₂-LaF₃-AlF₃-NaF (ZBLAN) fiber lasers is investigated. Fiber pigtails by coating high-reflective visible dielectric films are utilized as fiber mirrors (FMs) to construct compact all-fiber laser cavity. Reflectance/transmittance of FMs is intentionally designed to balance net gains and reduce gain competition of different lasable wavelengths in the constructed fiber lasers. By using two selected FMs with high reflectivity at green-light and low reflectivity at red-light, simultaneous green and red laser emission in all-fiber Pr³⁺-doped ZBLAN fiber laser is obtained. Moreover, simultaneous orange and red laser emission is also achieved with another selected FM of high reflectivity at orange-light and low reflectivity at red-light. Our work will provide an effective and easy method to construct compact special fiber (e.g.,ZBLAN fiber, chalcogenide fiber) lasers.     

Photon echo relaxation in LaF3:Pr3+

We have observed deeply modulated photon echoes from Pr³⁺ ions in LaF₃ reflecting nuclear hyperfine interactions in both the ground ³H₄ and excited ³P₀ states. We infer splittings of 0.75 MHz for the ³P₀ state. Inhomogeneous broadening of the terminal levels is found to lead to echo modulation damping. A surprising concentration dependence of the photon echo relaxation rate is observed as well as a dramatically long-lived (3 min) stimulated photon echo.     

pr3+掺杂透明氟氧化物玻璃陶瓷的光谱特性

根据pr3+掺杂透明氟氧化物玻璃陶瓷(Pr(0.2)∶FOV)样品在室温下的吸收光谱,分别采用了标准和修正的Judd-Ofelt理论拟合出J-O强度三参量Mn.结果表明,此修正的J-O理论应用到Pr(0.2):FOV材料的跃迁强度计算中是合理的和必要的.并由此修正理论计算了各个激发态之间跃迁的振子强度、自发辐射速率、荧...     

High pressure luminescence spectra of CaMoO4:Pr3+

Steady state and time resolved luminescence measurements of CaMoO(4) doped with Pr(3+) as a function of hydrostatic pressure in the 1-175 kbar range are presented. It has been observed that with increasing pressure the spectral features shift towards lower energies, the decay times of both (3)P(0) and (1)D(2) emitting levels become shorter and the intensity of the (3)P(0) emission decreases to complete quenching at about 110 kbar, whereas that of the (1)D(2) emission increases in the 0-100 kbar range and then rapidly decreases when the pressure exceeds 127 kbar. A variation of the structure of the spectral manifolds indicates that a pressure induced phase transition of the host lattice occurs in the 80-100 kbar range. The quenching of the luminescence and the shortening of the decay times have been accounted for by means of a model that takes into account the role played by a praseodymium trapped exciton in the excited state dynamics of the investigated material.     

Luminescence properties of K1/2Bi1/2TiO3:Pr3+ and Na1/2Bi1/2TiO3:Pr3+

The luminescence properties of K(1/2)Bi(1/2)TiO(3):Pr(3+) and Na(1/2)Bi(1/2)TiO(3):Pr(3+) powders are investigated in the temperature range 10-600 K. The experimental data are interpreted on the basis of metal-to-metal charge transfer processes and by considering Bi(3+)-to-Pr(3+) sensitization effects.     

Quantum cutting in CaYAlO4: Pr3+, Yb3+

The deposition of a thin layer of a quantum-cutter material on top of silicon-based solar cells seems to be a promising solution to reduce the thermalization losses. This mechanism has been reported in materials codoped with Pr3+-Yb3+, where Pr3+ can sensitize two Yb3+ ions for one absorbed blue photon. In the present Letter, we analyze precisely energy transfers between Pr3+ and Yb3+ in CaYAlO4, and we measure a quantum-cutting rate of 145%. We show that a very efficient back transfer from Yb3+ toward the (1)G4 level of Pr3+ ion leads to a strong reduction of the quantum yield.     

硅酸锶中Pr3+的4f5d态的光谱特性及Pr3+→Gd3+的能量传递

本文研究了室温下Pr^3 在Sr2SiO4中的发射光谱和激发光谱，在激发光谱中，最低激发峰位置低于^1So能级位置，属于5d态的吸收。发射光谱主要由5d→4f的跃迁构成，未观测到Pr^3 和^3Po和^1D2的辐射跃迁。Pr^3 的掺杂浓度在0.01mol左右时，其发射强度接近最大。在Sr2SiO4:Pr^3 ,Gd^3 体系中，Pr^3 体系中，Pr^3 的5d→^3H4的跃迁与Gd^3 的^8S7/2→^6I能级的吸收跃迁相匹配，因此发生了Pr^3 →Gd^3的高效无辐射能量传递。固定Pr^3 的浓度时，随着体系中Gd^3 离子浓度的增加，Gd^3 的发射强度也随之增强，同时，Pr^3 的发射强度则逐渐下降。     

Non-radiative relaxation processes of the Pr3+ ion

Conclusions The³P₀→¹D₂ non-radiative decay rates A_NR of Pr³⁺ and the transition probabilities A_VIB for the vibronic³H₄→³P₀ excitation transitions of Pr³⁺ were measured at 4.2 K in several host lattices. Besides the well-known dependence on the number of phonons involved in the radiationless transition, the multiphonon relaxation rates are observed to be greatly enhanced by increasing covalency and/or decreasing Pr-ligand distances. The enhanced multiphonon relaxation is ascribed to a stronger electron-phonon coupling. The increase in the electron-phonon coupling strength is confirmed by the increase of the vibronic transition probabilities A_VIB in the same sequence as the A_NR rates. The observed host lattice dependence of A_NR can be qualitatively accounted for by a non-linear multiphonon relaxation mechanism. Under certain conditions (viz. low-lying 4f5d states, and a force constant stronger in the 4f5d than in the 4f² states) fast³P₀→¹D₂ non-radiative relaxation via intersystem crossing through the 4f5d state becomes the dominant relaxation mechanism, even at 4.2 K. Debye Institute, Utrecht University P. O. Box 80000, 3508 TA Utrecht, The Netherlands. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 4, pp. 63–71, July–August, 1995.     

Mg2+、Al3+离子增强SrTiO3:Pr3+荧光体发光性能的研究

采用溶胶凝胶法成功制备了SrTiO3:Pr3+、SrTiO3:Pr3+, Mg2+及SrTiO3:Pr3+,Al3+荧光粉.通过XRD、PL谱及第一性原理计算对样品的晶体结构、光谱特性及发光增强机制进行了研究.研究结果表明:共掺杂后,SrTiO3:Pr3+荧光粉为单一组成的SrTiO3立方相,主发射锋位于617 nm,对应于Pr3+离子的1D2→3H4跃迁发射.SrTiO3:Pr3+,Mg2+ 及SrTiO3:Pr3+, Al3+荧光粉的发光强度分别是SrTiO3:Pr3+荧光粉发光强度的7倍和2倍,但主要发光机制没有改变.Mulliken布局分析表明,Mg2+、Al3+离子的掺入使SrTiO3:Pr3+荧光粉中Ti-O及Pr-O键的化学键增强、键长变短,SrTiO3:Pr3+基质向Pr3+离子发光中心的能量传递效率提高,导致SrTiO3:Pr3+,Mg2+ 及SrTiO3:Pr3+,Al3+荧光粉的发光效率提高.     

Luminescence of Pr3+ and Nd3+ Ions in Double Molybdates

Physics of the Solid State - The optical spectra of samples of double zirconium molybdates activated by rare-earth Pr3+ and Nd3+ ions are studied. The presence of bands corresponding to the...     

计算光度法同时测定镧、铈、镨、钕

以二溴一氯-偶氮氯膦(DBC-CPA)为显色剂,并且在显色体系中加入不同量的EDTA-Na2P2O7作为竞争配位剂,使得4组分轻稀土组分间吸收光谱灵敏度的差别加大,从而增加了轻稀土混合物体系组分间吸收光谱的线性独立性,采用数值稳定性强的约束优化算法-可变容差法处理光谱数据,对不同深度比例的4组分轻烯土混合物体系(La^3 ,Ce^3 ,Pr^3 ,Nd^3 )的测定,取得了较为满意的结果.     

Downconversion for Solar Cells in YF3:Pr3+, Yb3+

ABSTRACT

Energy losses in solar cells caused by the spectral mismatch can be reduced by adapting the solar spectrum using a downconversion material where one higher energy visible photon is ‘cut' into two lower energy near-infrared photons that both can be absorbed by the solar cell. Downconversion with the (Pr³⁺, Yb³⁺) couple in YF₃ is investigated. Based on analysis of luminescence and diffuse reflectance spectra it is evident that two-step energy transfer takes place from the ³P₀ level of Pr³⁺ (around 490 nm) exciting two Yb³⁺ to the ²F_5/2 level giving emission around 980 nm. The transfer efficiency increases with Yb³⁺ concentration and is 86% for YF₃ doped with 0.5% Pr³⁺ and 30% Yb³⁺. Due to concentration quenching the intensity of emission from Yb³⁺ is strongly reduced and the ²F_5/2 emission intensity reaches a maximum for the sample with 0.5% Pr³⁺ and 2–5% Yb³⁺ at 300 K. Temperature dependent measurements reveal the role of the Pr^{3+ 1}G₄ level in the energy transfer between Pr³⁺ and Yb³⁺. Back-transfer of excitation energy from the Yb^{3+ 2}F_5/2 level to the ¹G₄ level of Pr³⁺ occurs and quenches the Yb³⁺ emission. The quenching is shown to become more efficient between 4 and 50 K due to faster phonon-assisted energy transfer between the Yb³⁺ donors. Upon raising the temperature from 50 to 300 K, the luminescence life time of the Yb³⁺ emission increases again because the small energy difference between the Pr³⁺ (¹G₄) level and the Yb³⁺ (²F_5/2) level (～300 cm^?1) which makes the ¹G₄ less efficient as a trap for the excitation energy. The present results give insight into factors involved in the concentration quenching in downconversion materials based on the (Pr³⁺, Yb³⁺) couple.     

Recombination processes in lanthanum beryllate single crystals doped with Ce3+ and Pr3+ ions

The paper presents experimental results on recombination processes in lanthanum beryllate (BLO) single crystals (undoped BLO, and doped with 0.5 at % by Ce³⁺ and Pr³⁺ ions) obtained using XRL-spectroscopy at T = 8, 80 and 290 K and thermoluminescence technique in the temperature range of 8–650 K. The paper discusses spectra of the steady-state XRL-luminescence recorded in the energy range from 1.5 to 6.2 eV at different temperatures between 8 and 290 K; temperature dependences of XRL intensity recorded in the temperature range from 8 to 650 K; thermoluminescence glow curves recorded in spectral-integrated regime after X-ray exposure at T₀ = 8 or 290 K.