Room Temperature Visible/Infrared Emission and Energy Transfer in Nd3+-Based Organic/Inorganic Hybrids

The photoluminescence features and the energy transfer processes of Nd³⁺-based siloxane-poly(oxyethylene) hybrids are reported. The host matrix of these materials, classed as di-ureasils, is formed by a siloxane backbone covalently bonded to polyether chains of two molecular weights by means of urea cross-links. The room-temperature photoluminescence spectra of these xerogels show a wide broad purple-blue-green band (350–570 nm), associated with the emitting centres of the di-ureasil host, and the typical near infrared emission of Nd³⁺ (700–1400 nm), assigned to the ⁴F_3/2 ⁴I_{9/2,11/2,13/2} transitions. Self-absorptions in the visible range, resonant with intra-4f³ transitions, indicate the existence of an energy conversion mechanism of visible di-ureasil emission into near infrared Nd³⁺ luminescence. The existence of energy transfer between the di-ureasil's emitting centres and the Nd³⁺ ions is demonstrated calculating the lifetimes of these emitting centres. The efficiency of that energy transfer changes both with the polymer molecular weight and the Nd³⁺ concentration.     

Judd–Ofelt analysis and photoluminescence properties of RE3+ (RE = Er & Nd): Cadmium lithium boro tellurite glasses

Rare earth (Er³⁺ and Nd³⁺) ions doped cadmium lithium boro tellurite (CLiBT) glasses were prepared by melt quenching method. The vis–NIR absorption spectra of these glasses have been analyzed systematically. Judd–Ofelt intensity parameters Ω_λ (λ = 2, 4, 6) have been evaluated and used to compute the radiative properties of emission transitions of Er³⁺ and Nd³⁺: CLiBT glasses. From the NIR emission spectra of Er³⁺: CLiBT glasses a broad emission band centered at 1538 nm (⁴I_13/2 → ⁴I_15/2) is observed and from Nd³⁺: CLiBT glasses, three NIR emission bands at 898 nm (⁴F_3/2 → ⁴I_9/2), 1070 nm (⁴F_3/2 → ⁴I_11/2) and 1338 nm (⁴F_3/2 → ⁴I_13/2) are observed with an excitation wavelength λ_exci = 514.5 nm (Ar⁺ Laser). The FWHM and stimulated emission cross-section values are calculated for Er³⁺ and Nd³⁺: CLiBT glasses. FWHM × σ_e^P values are also calculated for Er³⁺: CLiBT glasses.     

Size-dependent upconversion luminescence in YF3:Yb/Tm nanobundles

The upconversion luminescent properties of YF₃:Yb³⁺(20%)/Tm³⁺(1%) nanobundles with different sizes (240-500 nm in length) were studied under 980-nm excitation. Ultraviolet (¹I₆ → ³F₄/³H₆ and ¹D₂ → ³H₆), blue (¹D₂ → ³F₄ and ¹G₄ → ³H₆), red (¹D₂ → ³H₄, ¹G₄ → ³F₄, and ³F₃ → ³H₆), and near infrared (³H₄ → ³H₆) emissions were observed. The results indicated that the relative intensity of the ultraviolet to the blue as well as the blue to the near infrared increased with decreasing the size of nanobundles. Especially, the position of the dominant red emission peak varied with the size of nanobundles. As the length of nanobundles increased to 500 nm, unusual ³F₃ → ³H₆ transition was observed, which was theoretically explained considering the decrease of the nonradiative transition rate of ³F₃ → ³H₄.     

Photoluminescence properties of a novel phosphor, Na3La9O3(BO3)8:RE(RE=Eu,Tb)

The new oxyborate phosphors, Na₃La₉O₃(BO₃)₈:Eu³⁺ (NLBO:Eu) and Na₃La₉O₃(BO₃)₈:Tb³⁺ (NLBO:Tb) were prepared by solid-state reactions. The photoluminescence characteristics under UV excitation were investigated. The dominated emission of Eu³⁺ corresponding to the electric dipole transition ⁵D₀→⁷F₂ is located at 613 nm and bright green luminescence of NLBO:Tb attributed to the transition ⁵D₄→⁷F₅ is centered at 544 nm. The concentration dependence of the emission intensity showed that the optimum doping concentration of Eu and Tb is 30% and 10%, respectively.     

NaBaPOM4:Tb3+绿色荧光粉制备及其发光特性

采用高温固相法合成了NaBaPOM₄:Tb³⁺绿色荧光粉, 并研究了材料的发光性质. NaBaPOM₄:Tb³⁺材料呈多峰发射, 发射峰位于437、490、543、587和624 nm, 分别对应Tb³⁺的⁵D₃→⁷F₄和⁵D₄→⁷F_{J=6, 5, 4, 3}跃迁发射, 主峰为543 nm; 监测543 nm发射峰, 所得激发光谱由4f⁷5d¹宽带吸收(200-330 nm)和4f-4f 电子吸收(330-400 nm)组成, 主峰为380 nm. 研究了Tb³⁺掺杂浓度, 电荷补偿剂Li⁺、Na⁺、K⁺和Cl^-, 及敏化剂Ce³⁺对NaBaPOM₄:Tb³⁺材料发射强度的影响. 结果显示: 调节激活剂浓度、添加电荷补偿剂或敏化剂均可以在很大程度上提高材料的发射强度.     

Radiation-chemical yield of excited neodymium(III) ions in phosphorus oxychloride-based aprotic binary solvents

Results of measurements of the yield of radioluminescence photons from Nd³⁺ ions in POCl₃-SnCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ and POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions upon homogeneous excitation by uranium α-particles are presented. It was found that the radioluminescence intensity corresponding to the³ F _3/2 →⁴ I _11/2 transition of neodymium ions depends on the solvent composition. The radiation-chemical yield of excited Nd³⁺ ions is proportional to the neodymium concentration, being (1.50 ±0.05) and (0.23 ±0.02) excited ions per 100 eV in POCl₃-SnCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ and POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ systems, respectively, at [Nd³⁺] = 0.4 mol/l.     

不同掺杂浓度Tm3+：LiLuF4单晶的1800 nm荧光发射

采用坩埚下降法生长了Tm³⁺掺杂浓度为0.45%,0.90%,1.63%与3.25%（摩尔分数,x）的LiLuF₄单晶.测试了样品的电感耦合等离子体原子发射光谱（ICP-AES）、X射线衍射（XRD）谱、吸收光谱（1400-2000 nm）,并且分析比较了808 nm半导体激光器（LD）激发下荧光光谱. 结果表明：当Tm³⁺的浓度从0.45%变化到3.25%时,1800 nm处的荧光强度呈现了先增后减的趋势,当掺杂浓度约为0.90%时达到最大值,而位于1470 nm处的荧光强度则呈现了相反的趋势. Tm³⁺：³F₄能级的荧光衰减寿命随着掺杂浓度的增加不断减小. 1800 nm处的这种荧光强度变化归结于Tm³⁺离子间的交叉驰豫效应（³H₆,³H₄→³F₄,³F₄）和自身的浓度猝灭效应. 同时计算得到了浓度为0.90%的样品在1890 nm处的最大发射截面为0.392×10^-20 cm². 并且根据Judd-Ofelt 理论所得寿命和测定的荧光寿命计算得到了³F₄→³H₆的最大量子效率约为120%.     

Hydrothermal synthesis and luminescent properties of LuBO3:Tb microflowers

Hexagonal vaterite-type LuBO₃:Tb³⁺ microflower-like phosphors have been successfully prepared by an efficient surfactant- and template-free hydrothermal process directly without further sintering treatment. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectrometry, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL) and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The as-obtained phosphor samples present flowerlike agglomerates composed of nanoflakes with thickness of 40 nm and high crystallinity in spite of the moderate reaction temperature of 200 °C. The reaction mechanism has been considered as a dissolution/precipitation mechanism; the self-assembly evolution process has been proposed on homocentric layer-by-layer growth style. Under ultraviolet excitation into the 4f⁸→4f⁷5d transition of Tb³⁺ at 248 nm (or 288 nm) and low-voltage electron beam excitation, LuBO₃:Tb³⁺ samples show the characteristic green emission of Tb³⁺ corresponding to ⁵D₄→⁷F_{6, 5, 4, 3} transitions with the ⁵D₄→⁷F₅ transition (542 nm) being the most prominent group, which have potential applications in fluorescent lamps and field emission displays.     

Preparation and Optical Properties of Submicron SiO2 Spheres Doped with YAG:Nd3+ Nanocrystallites

The sol-gel technology has been applied to obtain SiO₂ spheres of submicron size. The spheres have been doped with YAG:Nd³⁺ nanocrystallites. The nanocrystallites have been obtained from aqueous solutions of citric acid, yttrium, aluminum and neodymium chlorides. The obtained gels have been heated up to 800°C. Emission spectra as well as the excited state lifetimes have been measured at room and liquid nitrogen temperatures. The structural characterization has been performed by means of transmission and scanning electron microscopies (TEM, SEM) and powder diffraction (XRD) measurements. We have observed that the YAG:Nd³⁺ nanocrystallites demonstrate pronounced dependence of the emission intensities on the excitation power as compared to the YAG:Nd³⁺ crystallites embedded into the submicron SiO₂ spheres. The results suggest that silica spheres/YAG:Nd³⁺ composites are expected to be good hosts for microlaser systems.     

DNA Intercalating Near-Infrared Luminescent Lanthanide Complexes Containing Dipyrido[3,2-a:2′,3′-c]phenazine (dppz) Ligands: Synthesis,Crystal Structures,Stability, Luminescence Properties and CT-DNA Interaction

In order to create near-infrared (NIR) luminescent lanthanide complexes suitable for DNA-interaction, novel lanthanide dppz complexes with general formula [Ln(NO₃)₃(dppz)₂] (Ln = Nd³⁺, Er³⁺ and Yb³⁺; dppz = dipyrido[3,2-a:2′,3′-c]phenazine) were synthesized, characterized and their luminescence properties were investigated. In addition, analogous compounds with other lanthanide ions (Ln = Ce³⁺, Pr³⁺, Sm³⁺, Eu³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Tm³⁺, Lu³⁺) were prepared. All complexes were characterized by IR spectroscopy and elemental analysis. Single-crystal X-ray diffraction analysis of the complexes (Ln = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Eu³⁺, Er³⁺, Yb³⁺, Lu³⁺) showed that the lanthanide’s first coordination sphere can be described as a bicapped dodecahedron, made up of two bidentate dppz ligands and three bidentate-coordinating nitrate anions. Efficient energy transfer was observed from the dppz ligand to the lanthanide ion (Nd³⁺, Er³⁺ and Yb³⁺), while relatively high luminescence lifetimes were detected for these complexes. In their excitation spectra, the maximum of the strong broad band is located at around 385 nm and this wavelength was further used for excitation of the chosen complexes. In their emission spectra, the following characteristic NIR emission peaks were observed: for a) Nd³⁺: ⁴F_3/2 → ⁴I_9/2 (870.8 nm), ⁴F_3/2 → ⁴I_11/2 (1052.7 nm) and ⁴F_3/2 → ⁴I_13/2 (1334.5 nm); b) Er³⁺: ⁴I_13/2 → ⁴I_15/2 (1529.0 nm) c) Yb³⁺: ²F_5/2 → ²F_7/2 (977.6 nm). While its low triplet energy level is ideally suited for efficient sensitization of Nd³⁺ and Er³⁺, the dppz ligand is considered not favorable as a sensitizer for most of the visible emitting lanthanide ions, due to its low-lying triplet level, which is too low for the accepting levels of most visible emitting lanthanides. Furthermore, the DNA intercalation ability of the [Nd(NO₃)₃(dppz)₂] complex with calf thymus DNA (CT-DNA) was confirmed using fluorescence spectroscopy.     

Enhanced ultraviolet up-conversion emissions of Tm/Yb codoped YF3 nanocrystals

Tm³⁺/Yb³⁺ codoped rod-like YF₃ nanocrystals were synthesized through a facile hydrothermal method. After annealing in an argon atmosphere, the nanocrystals emitted bright blue and intense ultraviolet (UV) light under a 980-nm continuous wave diode laser excitation. Up-conversion emissions centered at ∼291 nm (¹I₆ → ³H₆), ∼347 nm (¹I₆ → ³F₄), ∼362 nm (¹D₂ → ³H₆), ∼452 nm (¹D₂ → ³F₄), ∼476 nm (¹G₄ → ³H₆), ∼642 nm (¹G₄ → ³F₄), and ∼805 nm (³H₄ → ³H₆) were recorded using a fluorescence spectrophotometer. Especially, enhanced UV emissions were studied by changing Yb³⁺/Tm³⁺ doping concentrations, the annealing temperatures, and the excitation power densities. A possible mechanism, energy transfer-cross relaxation-energy transfer (ET-CR-ET), was proposed based on a simple rate-equation model to elucidate the process of the enhanced UV emissions.     

Luminescent Study on Nd3+ Complexes Containing Carboxylate‐Dithiolene and Alkoxide‐Dithiolene Ligands

Reaction of ligand L H₂ (4,5‐bis[carboxymethylthio]‐1,3‐dithiol‐2‐thione) with neodymium silyl‐amide (Nd[N(TMS)₂]₃; TMS= ‐SiMe₃), in a ratio 2:1, yields a neodymium‐dithiolene‐carboxylato complex ( 1 ) (Nd( L H) L ). Similarly, reaction of 2 equivalents of L′ H₂ (4,5‐bis[2′‐hydroxyethyl)thio]‐1,3‐dithiol‐2‐thione) and one equivalent of neodymium silyl‐amide (Nd[N(TMS)₂]₃) allowed the isolation of complex 2 , with a ligand:metal ratio of 3:2. ATR‐IR spectrum of 1 displays a broad band characteristic of an OH group showing that one carboxylate group remains protonated. Emission spectrum of complex 1 under excitation in the visible region (at 360 nm i.e. on the ligand) displayed typical emission bands of the Nd³⁺, showing that energy transfer from the ligand to the lanthanide was achieved (i.e. “antenna effect”). No significant quenching from the remaining –OH group was detected. In the case of complex 2 , the main emission bands characteristic of the Nd³⁺ ion have been observed, by excitation at 495 nm.     

Synthesis, vacuum ultraviolet and near ultraviolet-excited luminescent properties of GdCaAl3O7: RE (RE=Eu, Tb)

Vacuum ultraviolet (VUV) excitation and photoluminescent (PL) properties of Eu³⁺ and Tb³⁺ ion-doped aluminate phosphors, GdCaAl₃O₇:Eu³⁺ and GdCaAl₃O₇:Tb³⁺ have been investigated. X-ray diffraction (XRD) patterns indicate that the phosphor GdCaAl₃O₇ forms without impurity phase at 900 °C. Field emission scanning electron microscopy (FE-SEM) images show that the particle size of the phosphor is less than 3 μm. Upon excitation with VUV irradiation, the phosphors show a strong emission at around 619 nm corresponding to the forced electric dipole ⁵D₀→⁷F₂ transition of Eu³⁺, and at around 545 nm corresponding to the ⁵D₄→⁷F₅ transition of Tb³⁺. The results reveal that both GdCaAl₃O₇:RE³⁺ (RE=Eu, Tb) are potential candidates as red and green phosphors, respectively, for use in plasma display panel (PDP).     

Composition dependent frequency upconversion of Er/Yb-codoped lead chloride tellurite glasses

The green and red upconversion luminescence of Er³⁺ in lead chloride tellurite glasses excited at 980 nm is investigated. Three intense emission bands centered at 530, 545, and 658 nm corresponding to the transitions ⁴S_3/2→⁴I_15/2, ²H_11/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2, respectively, were simultaneously observed at room temperature. With increasing PbCl₂ content, the intensity of green (530 nm) emissions increase slightly, while the green (545 nm) and red (658 nm) emissions increase significantly. The results indicate that PbCl₂ has more influence on the green (545 nm) and red (658 nm) emissions than the green (530 nm) emission. The dependence of upconversion intensities on excitation power and possible upconversion mechanisms are discussed and evaluated.     

Rare-Earth Actived Sol-Gel Films for Scintillator Applications

Recently, there has been a growth of interest in new phosphors preparation for high resolution X-rays imaging systems. Sol-gel method has been used to synthesize europium doped gadolinium and lutetium oxide films. Structural and optical results are investigated and discussed on both Gd₂O₃:Eu³⁺ (5 mol%) and Lu₂O₃:Eu³⁺ (5 mol%). Those films are crystallized into cubic phase and present a density of 7.1 g/cm³ and 8.4 g/cm³ for Gd₂O₃:Eu³⁺ and Lu₂O₃:Eu³⁺ respectively. Room temperature emission spectra using an excitation of 468 nm was used to obtain the intense red emission ⁵D₀ ⁷F₂ (611 nm) of Eu³⁺. Scintillation properties at 611 nm are finally proved using X-rays excitation.     

Structural, spectroscopic and photoluminescence studies of LiEu(WO4)2−x(MoO4)x as a near-UV convertible phosphor

A series of lithium europium double tungsto-molybdate phosphors LiEu(WO₄)_2−x(MoO₄)_x (x=0, 0.4, 0.8, 1.2, 1.6, 2.0) have been synthesized by solid-state reactions and their crystal structure, optical and luminescent properties were studied. As the molybdate content increases, the intensity of the ⁵D₀→⁷F₂ emission of Eu³⁺ activated at wavelength of 396 nm was found to increase and reach a maximum when the relative ratio of Mo/W is 2:0. These changes were found to be accompanied with the changes in the spectral feature, which can be attributed to the crystal field splitting of the ⁵D₀→⁷F₂ transition. As the molybdate content increases the emission intensity of the 615 nm peak also increases. The intense red-emission of the tungstomolybdate phosphors under near-UV excitation suggests them to be potential candidate for white light generation by using near-UV LEDs. In this study the effect of chemical compositions and crystal structure on the photoluminescent properties of LiEu(WO₄)_2−x(MoO₄)_x is investigated and discussed.     

Effects of nano-YAG (Y3Al5O12) crystallization on the structure and photoluminescence properties of Nd3+-doped K2O–SiO2–Y2O3–Al2O3 glasses

Nd³⁺-doped precursor glass in the K₂O–SiO₂–Y₂O₃–Al₂O₃ (KSYA) system was prepared by the melt-quench technique. The transparent Y₃Al₅O₁₂ (YAG) glass–ceramics were derived from this glass by a controlled crystallization process at 750 °C for 5–100 h. The formation of YAG crystal phase, size and morphology with progress of heat-treatment was examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transformed infrared reflectance spectroscopy (FT-IRRS). The crystallite sizes obtained from XRD are found to increase with heat-treatment time and vary in the range 25–40 nm. The measured photoluminescence spectra have exhibited emission transitions of ⁴F_3/2 → ⁴I_J (J = 9/2, 11/2 and 13/2) from Nd³⁺ ions upon excitation at 829 nm. It is observed that the photoluminescence intensity and excited state lifetime of Nd³⁺ ions decrease with increase in heat-treatment time. The present study indicates that the incorporation of Nd³⁺ ions into YAG crystal lattice enhance the fluorescence performance of the glass–ceramic nanocomposites.     

Preparation and optical properties of SrF2:Eu nanospheres

SrF₂:Eu³⁺ nanospheres with homogeneous diameter have been synthesized by a microemulsion-mediated hydrothermal method for the first time, in which quaternary microemulsion of CTAB/water/cyclohexane/n-pentanol was used. The possible reaction mechanism and the luminescent properties of SrF₂:Eu³⁺ nanospheres were also investigated in this paper. The morphology and grain sizes of final products were characterized by field emission scanning electron microscopy and transmission electron microscopy, indicating that most of the products were nanospheres with an average diameter of ∼50 nm. Room-temperature emission spectra, recorded under 394-nm excitation, showed that the transition of ⁵D₀ → ⁷F₁ emission be dominating in SrF₂:Eu³⁺ nanospheres. From the dependence of the luminescence intensity on the concentration of Eu³⁺ ions, the optimal dopant concentration is 2 mol%.     

White-light-emitting long-lasting phosphorescence in Dy-doped SrSiO3

We report on a luminescent phenomenon in Dy³⁺-doped SrSiO₃ long-lasting phosphor. After irradiation by a 254-nm UV lamp for 5 min, the Dy³⁺-doped SrSiO₃ phosphor emits white light-emitting long-lasting phosphorescence for more than 1 h even after the irradiation source has been removed. Photoluminescence, long-lasting phosphorescence and thermoluminescence (TL) spectra are used to explain this phenomenon. Photoluminescence spectra reveal that the white light-emitting long-lasting phosphorescence originated from the two mixtures of Dy³⁺ characteristic luminescence, the 480-nm blue emission (⁴F_9/2→⁶H_15/2) and the 572-nm yellow emission (⁴F_9/2→⁶H_13/2). TL spectra shows that the introduction of Dy³⁺ ions into the SrSiO₃ host produces a highly dense trapping level at 377 K (0.59 eV), which is responsible for the long-lasting phosphorescence at room temperature. A possible mechanism of the long-lasting phosphorescence based on the experimental results is proposed. It is considered that the long-lasting phosphorescence is due to persistent energy transfer from the electron traps to the Dy³⁺ ions, which creates the persistent luminescence of Dy³⁺ to produce the white light-emitting long-lasting phosphorescence.     

Synthesis of Gd3PO7:Eu nanospheres via a facile combustion method and optical properties

Eu³⁺-doped Gd₃PO₇ nanospheres with an average diameter of ∼300 nm and a narrow size distribution have been prepared by a facile combustion method and structurally characterized by X-ray diffraction and field emission scanning electron microscopy. The luminescent properties were systemically studied by the measurement of excitation/emission spectra, and emission spectra under different temperatures, as well as by photostability. The strong red-emission intensity peaking at 614 nm originates the ⁵D₀→⁷F₂ transition and is observed under 254-nm irradiation, indicating that Eu³⁺ ions in Gd₃PO₇ mainly occupied non-centrosymmetry sites. The CIE1931 XY chromaticity coordinates of Gd₃PO₇:Eu³⁺ nanospheres are (x=0.654, y=0.345) in the red area, which is near the National Television Standard Committee standard chromaticity coordinates for red. Thus, Gd₃PO₇:Eu³⁺ nanospheres may be potential red-emitting phosphors for PDP and Xe-based mercury-free lamps.