ZnO:Tb纳米晶的协同发光现象

用光致发光的方法研究了掺铽的ZnO纳米晶这种新型掺杂纳米晶体系,观察到了其中的协同发光现象,指出ZnO纳米基质与掺入其中的铽中心之间存在有效的能量传递.该能量传递对稀土铽离子的特征发光起决定性的作用. 关键词： 光致发光 掺杂 纳米晶     

Efficient fluorescence of dissolved CaF2:Tb and CaF2:Ce, Tb nanoparticles through surface coating sensitization

Oleic acid (OA)-modified CaF₂:Tb³⁺ nanoparticles with various Tb³⁺ concentrations and CaF₂:Ce³⁺, Tb³⁺ nanoparticles were synthesized. The as-prepared nanoparticles were shown to be well dissolved in some common organic solvents, such as chloroform and toluene. The nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-Ray diffraction (XRD) and transmission electron microscopy (TEM). The investigation of fluorescence properties of CaF₂:Tb³⁺ nanoparticles showed that the Tb³⁺ ions could be sensitized efficiently by the surface coating of OA and CaF₂:Tb³⁺ nanoparticles with 10 mol% Tb³⁺ concentrations possess the highest emission intensity. The comparison of emission for CaF₂:Ce³⁺, Tb³⁺ and CaF₂:Tb³⁺ (10 mol%) nanoparticles revealed that the emission intensity of the former is about 4.5 times as strong as that of the latter.     

Sensitized luminescence through nanoscopic effects of ZnO encapsulated in SiO2:Tb sol gel derived phosphor

Terbium (1 mol%) doped ZnO-SiO₂ binary system was prepared by a sol-gel process. Nanoscopic effects of ZnO on the photoluminescence (PL) and the cathodoluminescence (CL) properties were studied. Defects emission from ZnO nanoparticles was measured at 560 nm and the line emission from Tb³⁺ ions in SiO₂:Tb³⁺ and ZnO-SiO₂:Tb³⁺ with a major peak at 542 nm was measured. The PL excitation wavelength for 542 nm Tb³⁺ emission was measured at ∼320 nm in both SiO₂:Tb³⁺ and ZnO-SiO₂:Tb³⁺. The CL data showed quenched luminescence of the ZnO nanoparticles at 560 nm from a composite of ZnO-SiO₂:Tb³⁺ and a subsequent increase in 542 nm emission from the Tb³⁺ ions. This suggests that energy was transferred from the ZnO nanoparticles to enhance the green emission of the Tb³⁺ ions. The PL and CL properties of ZnO-SiO₂:Tb³⁺ binary system and possible mechanism for energy transfer from the ZnO nanoparticles to Tb³⁺ ions are discussed.     

Luminescence studies on lanthanide ions (Eu, Dy and Tb) doped YAG:Ce nano-phosphors

Yttrium aluminum garnet nanoparticles both undoped and doped with lanthanide ions (Ce³⁺, Eu³⁺, Dy³⁺ and Tb³⁺) having average size around 30 (±3 nm) nm were prepared by glycine nitrate combustion method followed by annealing at a relatively low temperature of 800 °C. Increase in the annealing temperature has been found to improve the luminescence intensity and for 1200 °C heated samples there exists strong energy transfer from Tb³⁺ to Ce³⁺ ions in YAG:Ce(2%),Tb(2%) nanoparticles as revealed by luminescence studies. Co-doping the YAG:Ce nanoparticles with Eu³⁺ results in significant decrease in the emission intensity of both Ce³⁺ and Eu³⁺ ions and this has been attributed to the oxidation of Ce³⁺ to Ce⁴⁺ and reduction of Eu³⁺ to Eu²⁺ ions. Dy³⁺ co-doping did not have any effect on the Ce³⁺ emission as there is no energy transfer between Dy³⁺ and Ce³⁺ ions.     

Down-conversion process in Tb3+–Yb3+ co-doped Calibo glasses

The down-conversion process in Tb³⁺–Yb³⁺ co-doped Calibo glasses was studied. The emission, excitation and time-resolved measurements indicated the existence of an energy conversion through the excitation of Tb³⁺ ions to near-infrared emission by Yb³⁺ ions. The emission intensity dependence on excitation power confirms that the one-photon process is responsible for the Yb³⁺ emission. An enhanced Yb³⁺ emission was observed with Yb³⁺ doping and an optimal energy transfer efficiency of 32% was obtained before reaching near-infrared emission quenching. The mechanism of the non-resonant energy transfer from Tb³⁺ to Yb³⁺ is discussed in terms of the Tb³⁺–Yb³⁺ cross-relaxation and multiphonon decay processes.     

Luminescent properties of SrAl2B2O7: Ce, Tb

By using metal nitrates as starting materials, SrAl₂B₂O₇: Tb³⁺ and SrAl₂B₂O₇: Ce³⁺, Tb³⁺ powder phosphors were prepared by sol-gel method. X-ray diffraction (XRD), photoluminescence excitation and emission, as well as kinetic decays were employed to characterize the resulting samples. The results show that energy transfers from Ce³⁺ to Tb³⁺ ions. The emission intensity of Tb³⁺ ions in SrAl₂B₂O₇ could be greatly intensified when Ce³⁺ ions are doped into SrAl₂B₂O₇: Tb³⁺. The decay times of SrAl₂B₂O₇: Tb³⁺ were prolonged when Ce³⁺ ions were doped. The doping of Ce³⁺ ions not only improved the luminescent intensity, but also made the materials gets stable luminescent properties.     

The effect of codopants on spectral-kinetic characteristics of luminescence of scintillation glasses doped with terbium ions

The effect of Ce³⁺ and Pr³⁺ ions on spectral-kinetic characteristics of luminescence of lithium–phosphate–borate glasses is studied. It is shown that terbium ion luminescence caused by transitions from ⁵D₃ and ⁵D₄ multiplets to the ground 7FJ term is detected in samples containing Tb³⁺/Ce³⁺ and Tb³⁺/Pr³⁺. It has been found that an increase in the concentration of cerium ions from 0.2 to 1 wt % leads to an increase in the intensity of main luminescence bands of terbium ions. In Tb³⁺/Pr³⁺ glasses, a decrease in the relative light yield is observed with an increase in the concentration of Pr³⁺ ions. Processes of energy transfer between Tb³⁺/Ce³⁺ and Tb³⁺/Pr³⁺ ions are discussed.     

Effects of Silver Island Films on the Luminescent Intensity and Decay Times of Lanthanide Chelates

We examined the emission intensity and decay times of chelates Tb³⁺ and Eu³⁺ in micron thick samples between films of sub-wavelength size silver particles. We observed modest increases in emission intensities for the complexes between the silver particles as compared to between unsilvered quartz plates. The intensity decay times were dramatically decreased by the silver particles, which was in part mediated by diffusion toward the silver particles. These results indicated that luminescent lanthanides in close proximity to silver particles display increased rates of radiative decay. The use of luminophore-metallic surface interactions provides new opportunities for creation of luminescent probes with novel spectral properties.     

Enhanced luminescent properties of Y3Al5O12:Tb,Ce phosphor prepared by spray pyrolysis

Yttrium aluminum garnet (YAG) particles doped with Tb³⁺ or double doped with Tb³⁺ and Ce³⁺ were prepared by spray pyrolysis and characterized by photo- and cathode-luminescence. It was tried to incorporate a broad band of Ce³⁺ activator into the line peaks of Tb³⁺ in YAG host without the reduction of emission intensity. Ce-codoped YAG:Tb particles showed a broad band emission due to the d-f transition of Ce³⁺ and a reduction in the intensity of emission peaks due to ⁵D₃-⁷F_j (j=3, 4, 5, 6) transition of Tb³⁺ when they were excited by the ultraviolet light of 270 nm. These results supported that an effective energy transfer occurs from Tb³⁺ to Ce³⁺ in YAG host. Codoping Ce³⁺ ions greatly intensified the excitation peak at 270 nm for the emission at 540 nm of Tb³⁺, which means that more lattice defects, involving in the energy absorption and transfer to Tb³⁺, are formed by the Ce³⁺ codoping. The finding gives a promising approach for enhancing the luminescence efficiency.     

Cytotoxicity and inflammation in human alveolar epithelial cells following exposure to occupational levels of gold and silver nanoparticles

This study explores the viability of rare earth-doped zirconia nanophosphors as probable candidates for white light emission. Undoped ZrO₂ and single- and double-doped ZrO₂:M (where M?=?Tb³⁺ and Eu³⁺) nanophosphors have been synthesized using a simple sonochemical process. The products were characterized using X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS), and photoluminescence spectrophotometry. The SEM micrographs show that resultant nanoparticles have dendritic shape. TEM and HRTEM studies showed that the size of the majority of the nanoparticles were around 28?±?5?nm. Characteristic blue and green emission from Tb³⁺ ions and red from Eu³⁺ dopant ions were observed. The CIE coordinates of the double-doped ZrO₂:Tb³⁺ (1.2?%):Eu³⁺ (0.8?%) nanophosphor lie in the white light region of the chromaticity diagram and show promise as good phosphor materials for new lighting devices.     

Photoluminescence properties of Tb in porous silicon

Terbium (Tb³⁺)/porous silicon (PS) nanocomposites have been formed by impregnation of PS layer in chloride solution of terbium. Complete and uniform penetration of Tb³⁺ into PS layer is confirmed by Rutherford backscattering spectrometry (RBS) study. Photoluminescence (PL) spectrum shows that Tb³⁺ ions emit highly in the green region, while the PL band of PS is quenched. The emission of Tb³⁺ ions depends strongly on the excitation energy and shows a high efficiency at 488 nm corresponding to the maximum absorption band in terbium. A systematic study of the PL versus annealing temperature was performed. It shows an important improvement of the PL intensity for 700°C temperature annealing.     

Enhanced luminescent properties and optical absorption of γ-irradiated KI: Ce, Tb crystals

This paper reports that KI doped with Ce³⁺ or double doped with Tb³⁺ and Ce³⁺ were prepared by the Bridgman-Stockbarger method and characterized by optical absorption photoluminescence (PL), thermoluminescence (TL), photostimulated emission (PSL) and TL emission. The optical absorption measurement indicates that F and V₁, V₂ centers are formed in the crystals during the γ irradiation process. It was attempted to incorporate a broad band of Ce³⁺ activator into the narrow band emission of Tb³⁺ in the KI host without the reduction of emission intensity. Ce³⁺-co-doped KI and Tb crystals showed a broad band emission due to the d-f transition of Ce³⁺ and a reduction in the intensity of emission peaks due to the ⁵D₃-⁷F_j (j=3,4,5,6) transition of Tb³⁺, when they were excited at 240 nm.These results supported that an effective energy transfer occurs from Tb³⁺ to Ce³⁺ in the KI host. Co-doping Ce³⁺ ions greatly intensified the excitation peak at 260 nm for the emission at 393 nm of Tb³⁺, which means that more lattice defects, involved in the energy absorption and transfer to Tb³⁺, are formed by the Ce³⁺ co-doping. The integrated light intensity is an order of magnitude higher as compared to the undoped samples for similar doses of irradiation and heating rates. The defects generated by irradiation were monitored by optical absorption and TSL Trap parameters for the TL process are calculated and presented.     

White light emission from sonochemically synthesized rare earth doped ceria nanophosphors

Undoped CeO₂, and single and triple doped CeO₂:M (where M=Dy³⁺, Tb³⁺and Eu³⁺) nanophosphors were synthesized through a simple sonochemical process and characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), EDS and photoluminescence (PL) spectrophotometry. The TEM micrographs show that resultant nanoparticles have flower-like shape. The doped samples showed multicolor emission on single wavelength excitation. Energy transfer was observed from host to the dopant ions. Characteristic blue emission from Dy³⁺ ions, green from Tb³⁺ ions and red from Eu³⁺ ions were observed. The CIE coordinates of the triple doped Ce_0.86Dy_0.005Tb_0.055Eu_0.08O₂ nanoflowers lie in the white light region of the chromaticity diagram and show promise as good phosphor materials for new lighting devices.     

Ultraviolet and visible upconversion emission in Tb3+/Yb3+ co-doped fluorophosphate glasses

Ultraviolet and visible upconversion emissions in Tb³⁺/Yb³⁺ co-doped YF₃–BaF₂–Ba(PO₃)₂ glasses were observed under 980-nm laser diode excitation. The dependence of the emission intensities of Tb³⁺ on the pump power reveals that two-photon processes account for blue cooperative emission of Yb³⁺ at 476 nm and green upconversion emission of Tb³⁺ at 543 nm, and three-photon processes for ultraviolet emission of Tb³⁺ in the wavelength range of 379–435 nm. The effects of Tb³⁺ concentration on the emission intensity and the lifetime of Tb³⁺ and Yb³⁺ are investigated in detail. It is found that the cooperative energy transfer from a pair of excited Yb³⁺ ions to a ground Tb³⁺ ion is responsible for the appearance of blue and green upconversion emissions due to the ⁵D₄→⁷F _J (J=6,5,4,3) transitions of Tb³⁺, and the resonance energy transfer from Yb³⁺ to Tb³⁺ accounts for the population on the ⁵D₃,⁵G₆ level and ultraviolet upconversion emission.     

Enhanced luminescence and degradation of SiO2:Ce,Tb powder phosphors prepared by a sol-gel process

Enhanced green photoluminescence and cathodoluminescence (CL) from Tb³⁺ ions due to co-doping with Ce³⁺ ions were observed from SiO₂:Ce,Tb powder phosphors prepared by a sol-gel technique. Blue emission from the Ce³⁺ ions was completely suppressed by Tb co-doping, presumably due to energy transfer from Ce³⁺ to Tb³⁺. In addition, the green CL intensity from SiO₂:Ce,Tb degraded by ∼50% when the powders were irradiated for 10 h with a 2 keV, 54 mA/cm² beam of electrons in an ultra-high vacuum chamber containing either 1×10⁻⁸ or 1×10⁻⁷ Torr O₂. Desorption of oxygen from the surface was observed during the decrease of CL intensity. The mechanisms for energy transfer from Ce³⁺ ions to Tb³⁺ ions to enhance the green luminescence, and mechanisms for desorption of oxygen from the phosphor surface that would result in decreased CL intensity are discussed.     

Enhancement of Tb emission by non-radiative energy transfer from Dy in silicate glass

A study of energy transfer was performed in dysprosium-terbium-doped silicate glasses at room temperature. Enhancement of the Tb³⁺ emission and a decrease in the Dy³⁺ emission are observed as a result of energy transfer from Dy³⁺ ions to Tb³⁺ ions. The energy transfer efficiencies, transfer probabilities, as well as average donor-acceptor distances were also calculated. It is concluded that the energy transfer mechanism between Dy³⁺ and Tb³⁺ ion is mainly electric dipole-dipole in nature.     

Luminescence properties of Tb doped and Tm/Tb/Sm co-doped glasses for LED applications

Tb³⁺ ions doped and Tm/Tb/Sm co-doped glasses for light-emitting-diodes (LED) applications have been synthesized by melt quenching method. Their photoluminescence properties were studied by emission and excitation spectra. The ⁵D₃ and ⁵D₄ emission of Tb³⁺ can be varied by adjusting Tb³⁺ concentrations and the compositions of glass matrix. Blue, green and reddish orange emission bands were observed in the emission spectra of Tm/Tb/Sm co-doped glasses. The combination of these emission bands allows the realization of white light when the glasses are excited by near ultraviolet light. In addition, the relative intensity ratios of respective emission lines are dependent on the composition of glasses and the excitation wavelength.     

Energy transfer from benzoic acid to lanthanide ions in benzoic acid-functionalized lanthanide-doped CaF2 nanoparticles

The preparation of benzoic acid-functionalized CaF₂:Ln³⁺ (Ln = Eu or Tb) nanoparticles and their sensitized luminescence are described in this report. First, to achieve sufficient proof for energy transfer from benzoic acid (BA) to lanthanide ions doped in nanoparticles, we employ Eu³⁺ as the microscopic probe and investigate the luminescent spectra of benzoic acid-functionalized CaF₂:Eu³⁺ (BA-CaF₂:Eu³⁺) nanoparticles. Next, to further reveal the difference between sensitized luminescence and common luminescence for Eu³⁺ doped in CaF₂ nanoparticles, we study the emission spectra of BA-CaF₂:Eu³⁺ nanoparticles excited at 286 nm and 397 nm, respectively. Finally, we analyze and compare the luminescent spectra of BA-CaF₂:Tb³⁺ and CaF₂:Ce³⁺, Tb³⁺ nanoparticles in detail. Our results indicate that both Eu³⁺ and Tb³⁺ doped in CaF₂ nanoparticles can be efficiently sensitized through benzoic acid.     

Photoluminescence investigations of Zn2SiO4 co-doped with Eu and Tb ions

Zinc silicate phosphors co-doped with Eu³⁺ ions and also with both Eu³⁺ and Tb³⁺ ions were prepared by high temperature solid state reaction in air or reducing atmosphere. The luminescence characteristics of the prepared phosphors were investigated. While in the samples prepared in air, Eu³⁺ emission was found to be dominant over Tb³⁺ emission, in the samples prepared in reducing atmosphere, intense Eu²⁺ emission at 448 nm was found to be predominant over narrow Tb³⁺ emission. Luminescence studies showed that Eu³⁺ ions occupy asymmetric sites in Zn₂SiO₄ lattice. The intense f-f absorption peak of Eu³⁺ at 395 nm observed in these phosphors suggests their potential as red emitting phosphors for near ultra-violet light emitting diodes.     

White light generation through the zinc metaphosphate glass activated by Ce, Tb and Mn ions

The photoluminescence of Ce³⁺, Tb³⁺ and Mn²⁺ ions was investigated in the Zn(PO₃)₂ glass. The blue and green emissions of Tb³⁺ ions and the red emission of Mn²⁺ ions are enhanced upon UV excitation through a non-radiative energy transfer from Ce³⁺ to Tb³⁺ and Mn²⁺ ions. The efficiency of this transfer was estimated in at least 62%. It is demonstrated that this glass activated with three ions (Ce³⁺, Tb³⁺ and Mn²⁺) can generate white light emission (x=0.420 and y=0.423 chromaticity coordinates and 3440 K colour temperature) under excitation at 254 nm, i.e., using an AlGaN-based LED as excitation source.