Anomalies in the concentration quenching of luminescence in doped Y2SiO5:Pr3+ nanocrystals

In Y₂SiO₅:Pr³⁺ nanocrystals, an ordered phase is observed in the ¹ D ₂ luminescence decay curves of Pr³⁺ ions at their anomalously low concentration (0.5 at %). This effect is caused by the predominant accumulation of activator ions near the nanocrystal surface, which provides relaxation of the elastic strains arising as a result of the misfit between the ionic radii of Pr³⁺ and Y³⁺. The concentration quenching of Pr³⁺ luminescence is due to cooperative cross relaxation.     

Strong segregation of doped ions in Y2SiO5:Pr3+ nanocrystals

Strong temperature controlled segregation of doped ions in Y₂SiO₅:Pr³⁺ nanocrystals detected by spectroscopic techniques is reported. The elastic interactions stimulate Pr³⁺ segregation thus leading to non-uniform distribution of doped ions, pair formation and, as a consequence, to abnormal low threshold of luminescence concentration quenching for Y₂SiO₅:Pr³⁺ nanocrystals.     

Concentration quenching anomalies of activated Y<Subscript>2</Subscript>SiO<Subscript>5</Subscript>:Pr<Superscript>3+</Superscript> nanocrystal luminescence

For the fist time in Y₂SiO₅:Pr³⁺ nanocrystals, the ordered stage in the ¹ D ₂ luminescence decay curves for Pr³⁺ ions has been observed at anomalously low doped ion concentration (0.5 at %). This effect is caused by preferred location of the activator ions in the near-surface layer of the nanocrystal that provides the relaxation of elastic tension arising due to the difference of ionic radii of Pr³⁺ and Y³⁺ ions. Concentration quenching of Pr³⁺ luminescence is caused by the cooperative cross-relaxation.     

Optical spectroscopy of Ca3Sc2Si3O12, Ca3Y2Si3O12 and Ca3Lu2Si3O12 doped with Pr

The silicates Ca₃Sc₂Si₃O₁₂, Ca₃Y₂Si₃O₁₂ and Ca₃Lu₂Si₃O₁₂, both undoped and doped with Pr³⁺ ions, have been synthesized by solid-state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchrotron radiation. All doped samples have shown efficient 5d-4f emission upon direct VUV excitation of 5d levels, but only Ca₃Sc₂Si₃O₁₂:Pr³⁺ shows luminescence upon interband VUV or X-ray excitation. The VUV excited emission spectra of Ca₃Y₂Si₃O₁₂:Pr³⁺ and Ca₃Lu₂Si₃O₁₂:Pr³⁺ show features attributed to emission from two distinct sites accommodating the Pr³⁺ dopant. The decay kinetics of the Pr³⁺ 5d-4f emission in Ca₃Sc₂Si₃O₁₂:Pr³⁺ upon VUV excitation across the band gap are characterized by decay times in the range 25-28 ns with no significant rise after the excitation pulse. They appear to be faster upon X-ray irradiation than for VUV excitation. Weak afterglow components are attributed to defect luminescence.     

真空紫外光激发下掺Pr3+铝酸盐的自陷激子对Pr3+发光的影响

研究了SrAl₁₂O₁₉:Pr³⁺ 和Y₃Al₅O₁₂(YAG):Pr³⁺ 在20K, 77K和300K的真空紫外(VUV)光谱，二者除了表现出Pr³⁺特有的发射性质外，还产生了一种特殊的发射现象，即自陷激子(STE)发射,并且其随着稀土离子浓度和温度的降低而增强. 还着重讨论了自陷激子对Pr³⁺发光的影响. 关键词： 自陷激子 真空紫外 3+')" href="#">Pr³⁺ 本征激发     

The effect of Gd3+ on the Eu3+ luminescence in RbGd3F10: Eu3+ compounds

Eu³⁺ luminescence is studied in the two polymorphic forms of RbGd₃F₁₀: Eu³⁺. In the phases where Gd³⁺ is partly replacedby Y³⁺ in order to obtain an independent variation of Eu³⁺ concentration, the quenching of Gd³⁺ luminescence by Eu³⁺ ions takes place very quickly with increasing Eu³⁺ concentration. So the transfer between Gd³⁺ and Eu³⁺ is very efficient. Besides, an important self quenching occurs as well between Gd³⁺ ions as between Eu³⁺ ions, showing strong interactions.     

Fundamental aspects of activated nanocrystal luminescence and possible applications

Presented results of complex study of relaxation processes and interionic interaction in Y₂SiO₅:Pr³⁺ and Lu₂SiO₅:Ce³⁺ nanocrystals clearly show two fundamental aspects: the phonon quantum confinement gives rise to the new fluorescence dynamics of doped ions; the developed surface of nanocrystals stimulates the irregular distribution of doped ions within the nanocrystal volume and could be the reason of new atomic arrangement of nanocrystal. Fluorescence spectrum of isolated Y₂SiO₅:Pr³⁺nanocrystal demonstrates the intense fluorescence from the high crystal field components of split ¹D₂ manifold of Pr³⁺ as the result of a suppression of phonon-assisted relaxation under the phonon quantum confinement. The direct comparison of the data obtained for nano- and bulk Y₂SiO₅:Pr³⁺ crystals has revealed that the concentration threshold of luminescence quenching is strikingly low for nanocrystals. This effect is caused by uphill diffusion of doped ions and preferred Pr segregation at the nanocrystal surface layer that provides the relaxation of elastic tension arising due to the difference of ionic radii of Pr³⁺ and Y³⁺. Lu₂SiO₅:Ce³⁺ nanocrystals which average size is 5 nm do not demonstrate the effect of energy storage as the result of atomic packing changing that does not permit the existence of electronic traps.     

Simultaneous three-photon absorption induced ultraviolet upconversion in Pr:Y2SiO5 crystal by femtosecond laser irradiation

Near-infrared to ultraviolet upconversion luminescence was observed in the Pr³⁺:Y₂SiO₅ crystal with 120 fs, 800 nm infrared laser irradiation. The observed emissions at around 270 nm and 305 nm could be assigned to 5d → 4f transitions of Pr³⁺ ions. The relationship between the upconversion luminescence intensity and the pump power of the femtosecond laser reveals that the UV emission belongs to simultaneous three-photon absorption induced upconversion luminescence.     

Growth and the luminescence properties of a lutetium gadolinium garnet doped with Ce3+ and Pr3+ ions

Crystals of lutetium gadolinium garnet solid solutions (Lu_{1 − x} Gd _x )Al₅O₁₂ (0 ≤ x ≤ 0.6) doped with Ce³⁺ and Pr³⁺ ions have been prepared by the horizontal directional crystallization method, and their optical and luminescence properties have been investigated. It has been established that the introduction of gadolinium into the lutetium garnet lattice leads to a decrease in the antisite luminescence (Lu_Al centers) in the UV spectral range and to sensitization of the Ce³⁺ ion luminescence. By contrast, the presence of gadolinium results in the quenching of the Pr³⁺ luminescence due to the nonradiative excitation transfer from Pr³⁺ ions to Gd³⁺ ions.     

Temperature-dependent photoluminescence properties of (Y, Lu)3Al5O12:Ce phosphors for white LEDs applications

The effects of the excitation wavelength, Ce³⁺ concentration and chemical substitution on the thermal quenching of Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺) phosphors were investigated over a temperature range from 30 to 250 °C. The quenching behavior exhibits a complex dependence on the excitation wavelength and Ce³⁺ concentration, which can be attributed to temperature-dependent absorption strength of the different f-d absorption bands and thermally activated concentration quenching with or without energy migrations between Ce³⁺ ions, respectively. With increasing Lu³⁺content the luminescence of (Y, Lu)₃Al₅O₁₂:Ce³⁺ phosphors shows a pronounced blueshift, and simultaneously the temperature quenching is obviously improved due to a decrease in Stokes shift.     

Enhancement of red spectral emission intensity of Y3Al5O12:Ce phosphor via Pr co-doping and Tb substitution for the application to white LEDs

We have enhanced color-rendering property of a blue light emitting diode (LED) pumped white LED with yellow emitting Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) phosphor using addition of Pr and Tb as a co-activator and host lattice element, respectively. Pr³⁺ addition to YAG:Ce phosphor resulted in sharp emission peak at about 610 nm through ¹D₂→³H₄ transition. And when Tb³⁺ substituted Y³⁺ sites, Ce³⁺ emission band shifted to a longer wavelength due to larger crystal field splitting. Y₃Al₅O₁₂:Ce³⁺, Pr³⁺ and (Y_1−xTb_x)₃Al₅O₁₂:Ce³⁺ phosphors were coated on blue LEDs to fabricate white LEDs, respectively, and their color-rendering indices (CRIs, R_a) were measured. As a consequence of the addition of Pr³⁺ or Tb³⁺, CRI of the white LEDs improved to be R_a=83 and 80, respectively. Especially, blue LED pumped (Y_0.2Tb_0.8)₃Al₅O₁₂:Ce³⁺ white LED showed both strong luminescence and high color-rendering property.     

In situ sol-gel composition of multicomponent hybrid precursors to luminescent novel unexpected microrod of Y2SiO5:Eu employing different silicate sources

Y₂SiO₅ doped with Eu³⁺ were in situ synthesized by a hybrid precursor assembly sol-gel technology employing four different silicate sources, 3-aminopropyl-trimethoxysilane (APMS), 3-aminopropyl-triethoxysilane (APES), 3-aminopropyl-methyl-diethoxysilane (APMES) and tetraethoxysilane (TEOS), respectively. The SEM result shows that there exist some novel unexpected morphological microrod structures owing to using the crosslinking reagents other than TEOS as silicate source. The photoluminescent properties of Y₂SiO₅:Eu³⁺ have been studied as a function of Eu³⁺ doping concentration. A cross-relaxation process between identical Eu³⁺ ions results in the quenching of the ⁵D₁ emission for high concentration sample.     

Luminescence of La and Sc impurity centers in YAlO3 single-crystalline films

The luminescence of La_Y³⁺ and Sc_Y³⁺ and Sc_Al³⁺ centers created by lanthanum and scandium ions at Y³⁺ and Al³⁺ cation sites of YAlO₃ perovskite lattice was investigated. The features of emission of excitons localized at the mentioned centers in YAlO₃:La and YAlO₃:Sc single-crystalline films were analyzed by means of time-resolved emission spectroscopy and luminescence decay kinetics measurements under excitation by synchrotron radiation at 9 and 300 K.     

TeO2-ZnO-Na2O-K2O玻璃中Er3+离子掺杂浓度对其发光及荧光寿命的影响

测量了不同掺杂浓度下Er³⁺离子在碲酸盐玻璃中的吸收光谱、发射光谱和Er3+离子的荧光寿命，计算了Er³⁺离子的发射截面σ_e,分析 了Er ³⁺离子掺杂浓度对其发光强度和荧光寿命的影响.结果表明，Er³⁺离子掺 杂浓度较低时，对其荧光强度和荧光寿命没有显著的影响；掺杂浓度高时，出现了浓度猝灭 效应，使Er³⁺离 子荧光光强度降低，荧光寿命下降.实验确定了掺杂浓度最优值，同时对浓度猝灭机制进行 了分析. 关键词： 碲锌碱玻璃 3+离子')" href="#">Er³⁺离子 掺杂浓度 发光和荧光寿命     

Luminescence of Pr3+-Activated fluorides

The strong dependence of the emission spectrum of YF₃:Pr³⁺ on excitation source (228.8 nm, 213.9 nm or cathode rays) is ascribed to two different types of Pr³⁺ sites: one with a relatively strong crystal field and the other with a relatively weak crystal field. The presence of the latter is connected with the conversion of one short-wave UV (? 215 nm) photon into two visible photons. Two-photon luminescence of Pr³⁺ was also found for α-NaYF₄ and LaF₃, but not for CaF₂ and BaF₂ due to the too strong crystal field in these lattices. The occurrence of two-photon Pr³⁺ luminescence is compared with the intensity of the IR-excited green emission of the corresponding Yb³⁺, Er³⁺-activated lattices. The intensity of the Pr³⁺ luminescence at shortwave UV excitation (213.9 nm) is rather weak. Luminescence of reasonable efficiency is, however, observed on excitation with cathode rays.     

Preparation and optical properties of Ag enwrapped Y2O3:Eu nanoparticles in solution and in powders

Ag enwrapped Y₂O₃:Eu³⁺ nanoparticles were prepared by a wet chemistry method, which was dispersed in liquid (glycol) or dried to powders. Their luminescence properties were studied in comparison to those in the un-enwrapped ones. The results demonstrated that in glycol the ⁵D₀-⁷F₂ transitions for Ag enwrapped Y₂O₃:Eu³⁺ nanoparticles became stronger than that for un-enwrapped ones, while the excitation charge transfer band shifted blue. On the contrary, the ⁵D₀-⁷F₂ transitions in Ag enwrapped Y₂O₃:Eu³⁺ powders became weaker than those in the un-enwrapped ones. It was suggested that in liquid the Ag shells thinly deposited in the surface of Y₂O₃:Eu³⁺ and insulated the Y₂O₃:Eu³⁺ from the liquid, which contained large organic vibration modes. As a result, the surface nonradiative energy transfer from Eu³⁺ to the organic modes decreased, and emission intensity of ⁵D₀-⁷F₂ increased. In the Y₂O₃:Eu³⁺ powders, the Ag shells absorbed the excitation light, leading to the decrease in excitation density and the intensity of ⁵D₀-⁷F₂.     

Probing of surface Eu ions present in ZnO:Eu nanoparticles by covering ZnO:Eu core with Y2O3 shell: Luminescence study

Eu³⁺ doped ZnO nanoparticles are known to have significance extent of surface Eu³⁺ ions due to a large difference in ionic radii. Effect of such Eu³⁺ ions on the luminescence properties of ZnO:Eu nanoparticles has been understood from the luminescence studies of ZnO:Eu nanoparticles covered with Y₂O₃ shell. Based on the asymmetric ratio of luminescence and extent of energy transfer, it is established that when ZnO:Eu nanoparticles are covered with Y₂O₃ shell, a part of Eu³⁺ ions present with ZnO:Eu core migrate to Y₂O₃ shell and occupy Y³⁺ lattice positions.     

Luminescent properties of trivalent praseodymium-doped lanthanum aluminum germanate LaAlGe2O7

The luminescent characteristics of Pr³⁺-activated LaAlGe₂O₇ were investigated. In response to excitement using 448 nm blue light, the emission spectra involved most of the ³P₀→³H_J transitions. The dominant emission came from the ³P₀→³H₄ transition at 487 nm. ¹D₂ fluorescence quenching was observed in highly doped samples and is related to the cross-relaxation processes among neighboring Pr³⁺ ions. In contrast with conventional Pr³⁺-activated phosphors, the extraordinary excitation spectra showed only intense f-f transition of Pr³⁺ ions, while the 4f-5d transition was eliminated. This is ascribed to photoionization. By analyzing absorption and excitation spectra, it is recognized that no efficient energy transfer occurs between Pr³⁺ and the host lattice in LaAlGe₂O₇.     

Laser induced emission spectra of Pr3+ in CaF2 at low temperatures

The luminescence spectra of Pr³⁺ in CaF₂, excited with the 4765.05 Å line of the argon ion laser at low temperatures, consist of many more emission lines than the maximum allowed via the ³P₀→³H_4,5,6; ³F_2,3,4 transitions of a single Pr³⁺-site. Based upon their intensity, appropriate splittings and concentration dependence, these emission lines are divided into three groups, attributed to different sites of Pr³⁺ in CaF₂. The existence of Pr³⁺ ions in defect sites of different symmetries is supported by theoretical calculations. The laser emission spectra of Pr³⁺ at low temperatures are compared with room temperature emission spectra obtained with excitation of the ³P₀ state alone, and with low temperature spectra of Pr³⁺ in different hosts, reported in the literature.     

Photoluminescence and gamma-ray irradiation of SrAl2O4:Euand Y2O3:Eu phosphors

Y₂O₃:Eu³⁺ phosphor is a very attractive material for use as a red phosphor in many fields. SrAl₂O₄:Eu²⁺ belongs to long lasting phosphor (LLP) and it is a useful bluish-green luminescence material, which can also be a promising candidate as a simple and easy-to-use radiation detection element for visual display of two dimensional radiation distributions. In the present study, both these two kinds of phosphors were synthesized using high temperature solid state reactions. In our work, the influence of gamma-ray irradiation on the properties of these two kinds of phosphors was studied by comparing photoluminescence, brightness and the decay curve of unirradiated and gamma-ray-irradiated samples. Conclusions from the present work can be briefly summarized as follows. In irradiated samples, the brightness is decreased without sensible change in the wavelength distribution of the luminescence spectrum and in the decay kinetic upon gamma exposure. Moreover, the emission due to Eu³⁺→Eu²⁺ conversion in Y₂O₃:Eu³⁺ phosphors was not observed in our sample after irradiation to high exposure. Also the brightness of SrAl₂O₄:Eu²⁺ phosphor turned out to decrease after the exposition to ionizing radiation while the luminescence wavelength distribution remained unchanged. The reason for the effect of gamma-ray irradiation on the properties of phosphors is also discussed in the paper.