Nonradiative energy transfer from Mn2+ to Eu3+ in K2CaP2O7:Mn2+,Eu3+ phosphor

A series of color tunable phosphors K₂Ca_1?x?yP₂O₇:xMn²⁺, yEu³⁺ are synthesized by solid state reaction method. The energy transfer phenomenon from Mn²⁺ to Eu³⁺ has been observed in the Mn²⁺/Eu³⁺ codoped non-magnetic K₂CaP₂O₇ host, which was confirmed by PL spectra and decay curves. The Mn²⁺→Eu³⁺ energy transfer is controlled by quadrupole–quadrupole interaction between sensitizer and activator. The maximum efficiency of energy transfer is estimated to be 33% with x=0.125 and y=0.03 in K₂Ca_1?x?yP₂O₇:xMn²⁺, yEu³⁺ phosphor. The phosphors can emit light from green to yellow and eventually to orange under 400 nm excitation by changing the Mn²⁺/Eu³⁺ content ratio, indicating that K₂CaP₂O₇: Mn²⁺, Eu³⁺ would be potential candidates for use in lighting and displays applications.     

Energy transfer from Tb3+ to Eu3+ ions sorbed on SrTiO3 surface

The energy transfer at room temperature between Tb³⁺ and Eu³⁺ ions sorbed onto SrTiO₃ powders is investigated, using Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS). Several published works deal with the energy transfer between two lanthanide ions in co-doped matrices but it is the first time that transfer processes between two lanthanide ions sorbed on a solid surface is reported. The results show that the energy transfer between sorbed Tb³⁺ and Eu³⁺ ions on strontium titanate is a non-radiative process and follows a dipole–dipole type interaction. Moreover, the higher the acceptor ions Eu³⁺ concentration, the more efficient the energy transfer.It is shown that no energy migration between the Tb³⁺ donor ions occurs. A formalism based on the model of Inokuti–Hirayama is used and allows one to fit the non-exponential Tb³⁺ fluorescence decay. It is thus possible to evaluate the critical radius (R₀) of the influence sphere of the sorbed Tb³⁺ ions. According to the previous works, two sorption sites are considered for the sorbed rare-earth. The calculated radii are similar to those obtained for other couples of donor–acceptor lanthanide ions reported in the literature.     

Luminescence properties of NaGd(PO3)4:Eu3+ and energy transfer from Gd3+ to Eu3+

The luminescence properties of polyphosphates NaEu _x Gd_(1?x)(PO₃)₄ (x = 0–1.00) and the energy transfer from Gd³⁺ to Eu³⁺ were studied. In undoped NaGd(PO₃)₄ sample, the photon cascade emission of Gd³⁺ was observed under ⁸S_7/2 → ⁶G_J excitation (201 nm) in which the emission of a red photon due to ⁶G_J → ⁶P_J transition is followed by an ultraviolet photon emission due to ⁶P_J → ⁸S_7/2 transition. When part of Gd³⁺ ions in the host NaGd(PO₃)₄ were substituted by Eu³⁺ ions, the NaGd(PO₃)₄:Eu³⁺ sample showed intensive red emission under 172-nm vacuum-ultraviolet (VUV) excitation which is suitable for mercury-free fluorescent lamps and plasma display panel applications. Based on the VUV–visible spectroscopic characteristics and the luminescence decay properties of NaGd(PO₃)₄:Eu³⁺, it was found that the quantum cutting by a two-step energy transfer from Gd³⁺ to Eu³⁺ can improve the red emission of Eu³⁺ ions under VUV excitation but only a part of the excitation energy in the excited ⁶P_J states within Gd³⁺ ions can be transferred to Eu³⁺ ions for its red emission, and the nonradiative energy transfer efficiencies from the excited ⁶P_J states within Gd³⁺ to Eu³⁺ were calculated.     

Eu2+在磷酸镧中的发光及Ce3+→Eu2+的能量传递

采用高温固相反应合成了LaPO₄:Eu²⁺和LaPO₄:Ce³⁺,Eu²⁺样品,报道了Eu²⁺在LaPO₄中的发光性质和Ce³⁺→Eu²⁺的能量传递现象。文中探讨了Ce³⁺→Eu²⁺的能量传递机理,根据Dexter电多极相互作用的理论证明其为偶极子偶极子相互作用的共振能量传递。     

Eu3+ luminescence and Gd3+-Eu3+ energy transfer in K5Li2GdF10:Eu3+

Polycrystalline samples of europium-doped K₅Li₂GdF₁₀ have been obtained by a slow cooling of melted compound and investigated using spectroscopy methods. Luminescence from the ⁵ D ₂ level of Eu³⁺ is found to be weak. Intense visible emission upon excitation into the ⁵ D ₂ or higher energy levels has been attributed to overlapping transitions from long-lived ⁵ D ₁ and ⁵ D ₀ levels. A strong increase of the ⁵ D ₀ emission at the expense of the ⁵ D ₁ emission occurs between 5 K and 25 K without significant change of the ⁵ D ₁ lifetime. To account for this, it is supposed that both the radiative and the nonradiative transition rates are temperature-dependent. Efficient energy transfer from the ⁶ G _J levels of Gd³⁺ to Eu³⁺ ions has been evidenced by excitation spectra in the VUV region and VUV-excited luminescence. It has been concluded that the cross relaxation contributes to the energy-transfer process. Received: 8 May 2001 / Accepted: 11 May 2001 / Published online: 25 July 2001     

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.     

荧光粉CaWO4：Eu3+中WO2-4与Eu3+间的能量转递*

通过高温固相法分别制备了CaWO4和CaWO4：1%Eu3+样品.测量了样品不同温度(10-300 K)的荧光光谱、荧光衰减曲线和时间分辨荧光光谱.样品的荧光光谱表明：在240 nm紫外光激发下,两个样品在430 nm处都展现出来源于WO2?4的蓝色发射;样品CaWO4：Eu3+的Eu3+(5D0→7F1,2,3,4)的特征发射则归属于WO2?4到Eu3+间的能量传递.由样品室温(300 K)荧光衰减曲线发现：纯CaWO4的荧光寿命为8.85μs, Eu3+掺杂之后WO2?4的荧光寿命缩短至6.27μs,这从另一方面证明了WO2?4与Eu3+间能量传递的存在.由荧光寿命得到T =300 K时, CaWO4：1%Eu3+中WO2?4与Eu3+间的能量传递效率(ηET)为29.2%,能量传递速率(ωET)为4.65×104 s?1.通过时间分辨荧光光谱,获得了从WO2?4到Eu3+之间的能量传递的时间演变过程,当温度由10 K增加到300 K时,能量传递出现的时间单调变小.测试了不同温度(10-300 K)对CaWO4：Eu3+的荧光寿命的影响,发现在10-50 K时, Eu3+的荧光寿命增加,但温度超过50 K时发生猝灭,荧光寿命开始下降;WO2?4的荧光寿命则是随着温度的升高逐渐缩短.     

Photoluminescence characteristics and energy transfer between Bi3+ and Eu3+ in Gd2O3: Eu3+, Bi3+ nanophosphors

Bi³⁺ and Eu³⁺ codoped cubic Gd₂O₃ nanocrystals were prepared by the Pechini sol-gel method. Their photoluminescent properties were investigated under ultraviolet light excitation. The introduction of Bi³⁺ ions broadened the excitation band of Eu³⁺ emission, of which a new strong band occurred ranging from 320 to 380 nm due to the 6s²→6s6p transition of Bi³⁺ ions, implying a very efficient energy transfer from Bi³⁺ ions to Eu³⁺ ions. Upon 325 and 355 nm light excitation, the luminescent intensity of Eu³⁺ ions was remarkably improved by the incorporation of Bi³⁺ ions. But a significant quenching of Eu³⁺ emission was observed under 266 nm light excitation when Bi³⁺ was codoped. The possible energy transfer processes between Bi³⁺ and Eu³⁺ were discussed. The decay curves of Eu³⁺ emission under the excitation of 266 nm pulsed laser were measured and gave further evidence for our discussion.     

Energy transfer between Eu3+ ions in a lattice with two different crystallographic sites: Y2O3:Eu3+, Gd2O3:Eu3+ and Eu2O3

The Eu³⁺ ion occupies two different crystallographic sites in (Y_1−xEu_x)₂O₃ and (Gd_1−xEu_x)₂O₃, with site symmetry S₆ and C₂. Energy transfer over more than 7 Å occurs from Eu³⁺ (S₆) ions to Eu³⁺ (C₂) ions. This is shown to be a direct one-phonon assisted process, in combination with a one-site resonant two-phonon assisted process at higher temperatures. For x = 1 there is energy migration over the Eu³⁺ (C₂) sublattice to quenching impurities. The presence of cooperative absorption points to superexchange interaction between the Eu³⁺ ions.     

Optical absorption and emission from irradiated RbMgF3:Eu2+ and KMgF3:Eu2+

The optical properties of irradiated RbMgF₃:Eu²⁺ and KMgF₃:Eu²⁺ have been investigated. Previous research has shown that Eu²⁺ ions in unirradiated RbMgF₃ give rise to broad band absorption around 250 nm and sharp intense line emission at 360 nm. When this material is irradiated little or no change occurs in the 250 nm absorption, but the lifetime of the Eu²⁺ 360 nm transition is reduced. In addition, new emission is observed at 680 nm. In the case of irradiated KMgF₃:Eu²⁺ two new emission bands are observed at 600 and 800 nm. All of these transitions have short lifetimes and are not due to Eu³⁺ ions.     

The energy transfer from Eu2+ to Tb3+ in calcium chlorapatite phosphor and its potential application in LEDs

Energy transfer from Eu²⁺ to Tb³⁺ was observed by investigating the optical properties from photoluminescence spectra and decay time curves in Tb³⁺ singly doped and Eu²⁺–Tb³⁺ co-doped calcium chlorapatite, Ca₅(PO₄)₃Cl (CPCl). It is dominated by the cooperation of a phonon-assisted energy transfer process and a non-radiative resonant energy transfer process caused by the exchange interaction. Eu²⁺–Tb³⁺ co-doped calcium chlorapatite phosphors in which Tb³⁺ can be efficiently excited by 400 nm are potential candidates for phosphor-converted LED.     

Photophysics of RbCl co-doped with Eu2+ and Eu3+

Excitation and luminescence spectra of RbCl co-doped with divalent and trivalent europium ions are reported. Spectral dips appearing in the blue emission from Eu²⁺ are resulted from the radiative energy transfer from Eu²⁺ to Eu³⁺ and consequently induces the luminescence from Eu³⁺ that is responsible for the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions. The induced luminescence has been characterized as a function of temperature and a decay time. In addition, the polarized emission from RbCl doped with only Eu²⁺ is also reported.     

Time resolved investigations of energy transfer in Eu3+∶Y2O3

The concentration dependence of the energy transfer from the Eu³⁺ ions at lattice sites of point symmetryC ₃ i to the Eu³⁺ ions at lattice sites of point symmetryC ₂ in Y₂O₃ has been investigated by analyzing the nonexponential fluorescence decay curves of the donors measured after excitation by a short optical light pulse. The simple model of a fixed interaction rangeR ₀ proved to be adequate to explain the experimental observations. An interaction range ofR ₀=8.7 Å was found in agreement with previous steady state experiments.     

Radiative energy transfer from Pb2+ to Eu2+ ions in NaCl,Kcl, and KBr single crystals

In the present work, the emission and excitation spectra of NaCl, KCl, and KBr doubly doped with europium and lead ions were investigated. In all cases, excitation with light lying in the A-band of the Pb²⁺ ions produces in addition to the ³P₁ → ³S_o Pb²⁺ emission, the 4f⁶ 5d (^t2g) → 4f⁷ europium emission. This fact indicates that energy transfer occurs from Pb²⁺ to Eu²⁺ ions. From the data obtained, it was determined that the energy transfer process is of a radiative nature and that it is more efficient in KCl than in either of NaCl or KBr. A possible explanation for this fact is given.     

KMgF3:Eu2+晶体中Eu2+的受激发射研究

二价铕离子(Eu2 )在KMgF3晶体中产生窄带线状发射,峰值位于360 nm.依据自身建立的激发态能量损耗模型,预测了4f7(6P7/2)→4f7(8S7/2)跃迁实现受激发射的可能性.采用ASE技术测得了KMgF3:Eu2 晶体360 nm发射的光学增益,得到净光学增益系数g=(11.4±3.2)cm-1,实验证实了理论预测.晶体退火或掺杂敏化离子Gd3 或Ce3 可以改善Eu2 的增益效果.     

纳米Gd2O3中两种格位Eu3+的电荷迁移态激发跃迁

观测了粒径分别为15,23,135m的立方相Gd2O3：Eu^3 的选择激发光谱、发射光谱和激发光谱。受强量子限域效应的影响,纳米Gd2O3：Eu^3 的激发光谱的强度表现出对颗粒尺寸的明显依赖性。用Jorgensen公式计算电荷迁移带的位置,与实验测得激发光谱中位置相一致。通过电荷迁移带不同位置的选择激发光谱可以分辨出立方相Gd2O3：Eu^3 中C2和S6格位Eu^3 的发光,从选择激发的发射光谱和激发光谱结果计算出C2和S6格位电荷迁移带的激发光谱,与实验结果相符合。     

Energy transfer induced Eu3+ photoluminescence enhancement in tellurite glass

In this work, structural, thermal and optical properties of Eu³⁺ doped TeO₂–La₂O₃–TiO₂ glass were investigated. The differential scanning calorimetry (DSC) measurements reveal an important stability factor ΔT=143.52 K, which indicates the good thermal and mechanical stabilities of tellurite glass. From the absorption spectrum, the optical band gap was found to be direct with E_g=3.23 eV. The temperature dependences of photoluminescence (PL) properties of Eu-doped and Eu–Tb codoped tellurite glass are investigated. As the temperature increases from 7 to 300 K, both the PL intensity and the PL lifetime relative to the ⁵D₂→⁷F₀ are nearly constant below 230 K and then an enhancement takes place. This anomalous feature is attributed to the thermally activated carrier transfer process from charged intrinsic defects states to Eu³⁺ energy levels.By co-doping tellurite glasses with Eu and Tb, a strong Eu³⁺ PL enhancement is shown due to excitation transfer from Tb³⁺ and intrinsic defects to Eu ions.