Excitation process and photoluminescence properties of Tb and Eu ions in SnO2 and in SnO2: Porous silicon hosts

Tin oxide (SnO₂)-layers-doped terbium and europium ions are elaborated by the sol-gel method on silicon substrates. After annealing at 500 °C, the transmission electron microscopy revealed a crystallization of tin oxide.The emission properties of rare-earth in SnO₂ are studied systematically against temperature annealing and Tb³⁺ concentration. The PL spectrum is optimal after annealing at 900 °C and the corresponding photoluminescence (PL) decay is nearly exponential, showing that the sample is homogenous and the PL process can be described by two levels system.The concentration effect shows a quenching of the PL intensity for Tb³⁺ concentration above 4%. From the investigation of the decay rate from the ⁷F₅ state within terbium concentration, we show that self-quenching is insured by dipole - dipole interaction. The evolutions of both PL intensity and PL lifetime versus temperature are studied. The PL intensity and PL lifetime are enhanced by deposing SnO₂:Tb³⁺ and SnO₂:Eu³⁺ in porous silicon. We show that an efficient excitation transfer from Si nanocrystallites to RE ions can occur.     

Syntheses of optically efficient (La1−x−yCexTby)F3 nanocrystals via a hydrothermal method

Optically efficient cerium and terbium doped lanthanide fluoride (La_1−x−yCe_xTb_y)F₃ nanocrystals with different doping concentrations have been synthesized by a hydrothermal route in the presence of ethylenediamine tetraacetic acid disodium salt (EDTA). The results showed that the formation of nanocrystals with different morphologies depends on terbium ion Tb³⁺ doping concentration, but independent of cerium ion Ce³⁺ doping concentration. With increase in Tb³⁺ doping concentration, the morphologies of nanocrystals evolved from a spherical shape to a plated-like one. In addition, both the photoluminescence quantum yield (PL QY) and the fluorescence lifetime of nanocrystals increased with the increase in Ce³⁺ doping concentration in cerium and terbium co-doped system. The PL QY reached up to 55%, and the lifetime up to 7.3 ms. Transmission electron microscopy (TEM), X-ray diffraction (XRD), selected area electron diffraction (SAED), X-ray fluorescence (XRF), energy dispersive spectroscopy (EDS), ultraviolet-visible (UV-vis) absorption, photoluminescence (PL) and infrared (IR) spectroscopies were employed to characterize the properties of nanocrystals. The growth mechanism of nanocrystals with different morphologies and optical properties of nanocrystals with different doping concentrations were investigated.     

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.     

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.     

Synthesis and photoluminescence of core–shell structured spherical SiO2@YPO4:Tb3+ phosphors via sol–gel process

Monodispersed SiO₂@YPO₄:Tb³⁺ core–shell submicrospheres were prepared through a simply homogeneous sol–gel method. The resulted SiO₂@YPO₄:Tb³⁺ core–shell particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence spectra (PL) and kinetic decays. The XRD results demonstrate that the YPO₄:Tb³⁺ layers begin to crystallize on the SiO₂ spheres after annealing at 500 °C and the crystallinity increases with raising the annealing temperature. The FTIR spectra show that the YPO₄:Tb³⁺ shell has linked to the silica surface through forming a Si–O–Y bond. SEM and TEM analysis indicate that SiO₂@YPO₄:Tb³⁺ core–shell submicrospheres have the regular microstructures and uniform size distributions. The emission spectra of the obtained submicrospheres are dominated by ⁵D₄–⁷F₅ transition of Tb³⁺ (545 nm, green), and the emission intensities of Tb³⁺ increase with increasing the annealing temperatures and the number of coating cycles. The optimum concentration for Tb³⁺ was determined to be 5 mol % of Y³⁺ in YPO₄ host.     

Preparation and luminescence properties of terbium-doped lanthanum oxide nanofibers by electrospinning

Terbium-doped lanthanum oxide (La₂O₃:Tb³⁺) nanofibers were prepared by electrospinning followed by calcination at high temperature. Thermogravimetric analyzer (TGA), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and photoluminescence (PL) were used to characterize the obtained fibers. The results reveal that the nanofibers have an average diameter of ca. 95±25 nm and are composed of pure La₂O₃ phase. Under the excitation of 274 nm light, the La₂O₃:Tb³⁺ nanofibers exhibit the characteristic emission resulting from the ⁵D₄→⁷F_J (J=3, 4, 5, 6) transitions of Tb³⁺ ions. And the PL emission intensity is stronger than that of their nanoparticle counterparts.     

Synthesis,studies and luminescent properties of terbium oxide-doped LaMn0.9Zn0.1O3+d nanoperovskite by sol–gel method

In this research, we report on the characterization of La_1?xTb_xMn_0.9Zn_0.1O_3+d (LTMZ) (0.0≤x≤0.32). Nanoparticles with high surface area were synthesized by the polymerized complex method based on the Pechini-type reaction. High-quality nanopowders with controlled stochiometry and microstructure were prepared in the temperature range of 700–800 °C for 6 h, with mean particle sizes of approximately 18.35 nm.

The synthesized materials were characterized by X-ray powder diffraction, fourier transform infrared spectrometry and photoluminescence (PL). PL measurements showed the characteristic green emission of Tb³⁺ ions in crystalline LTMZ powders due to the ⁵D ₄→⁷F _J transitions of the 4f electrons of Tb³⁺ ions. The structure, homogeneity and particle size of the obtained compounds during different stages were investigated by scanning electron microscopy.     

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.     

A novel green phosphor GdCaAlO4:Tb for PDP application

A novel green-emitting nano-sized phosphor, Tb³⁺-doped GdCaAlO₄ was synthesized with a precursor prepared by citrate sol-gel method at relatively low temperature. Powder X-ray diffraction (XRD) analysis confirmed the formation of GdCaAlO₄. Field-emission scanning electron microscopy (FE-SEM) observation indicated a narrow size-distribution of about ∼100 nm for the particles with a spherical shape. Upon excitation with near UV and vacuum ultraviolet (VUV) light, the phosphor showed strong green-emission peaked at around 546 nm, corresponding to the ⁵D₄→⁷F₅ transition of Tb³⁺, and the highest photoluminescence (PL) intensity at 546 nm was found at a content of about 12 mol% Tb³⁺. As the Tb³⁺ concentration increases, the fast diffusion of energy among terbium ions toward traps or impurities resulting in a decrease of the lifetime. The optical properties study suggests that it is a potential candidate for plasma display panels (PDPs) application.     

Excitation and emission processes of Tb in porous anodic alumina

The strong photoluminescence (PL) of porous anodic alumina (PAA) with terbium deposition is reported. PAA, which has a regular pore morphology, is considered an effective template for fabricating luminescent composites. Tb was deposited onto PAA films by immersion in alcoholic solution with terbium chloride followed by heat treatment. The PL spectra demonstrate typical bands of Tb³⁺ corresponding to ⁵D₄ → ⁷F_j (j = 3, 4, 5, 6,) electron transition, with the maximum at 18,360 cm⁻¹ (⁵D₄ → ⁷F₅). The PL mechanism of Tb³⁺ was systematically studied with annealing temperature. The non-radiative relaxation channel is provided by OH hydroxyls at the surface of porous anodic alumina and, after annealing at 900 °C, the PL yield is highly improved. The PL intensity of Tb³⁺ increases with laser power and a saturation phenomenon, associated with the ratio of Tb³⁺ to Tb⁴⁺ ions, is observed at approximately 90 W/cm². Based on a theoretical model, the optical cross-section σ of terbium in PAA is estimated, with a value close to that of other porous materials doped with the rare-earth elements.     

Synthesis, structural, optical and electrical properties of metal nanoparticle–rare earth ion dispersed in polymer film

Cu-nanoparticles have been prepared by ablating a copper target submerged in benzene with laser pulses of Nd:YAG (wavelength: 355, 532 nm and 1,064 nm). Colloidal nanoparticles have been characterized by UV–Vis spectroscopy and transmission electron microscopy. The obtained radius for the nanoparticles prepared using 1,064 nm irradiation lies in the range 15–30 nm, with absorption peak at 572 nm. Luminescence properties of Tb³⁺ ions in the presence and absence of Cu-nanoparticles have been investigated using 355 nm excitation. An enhancement in luminescence of Tb³⁺ by local field effect causing increase in lifetime of ⁵D₄ level of Tb³⁺ ion has been observed. Frequency and temperature-dependent conductivity of Tb³⁺ doped PVA thin films with and without Cu-nanoparticles have been measured in the frequency range 20 Hz–1 MHz and in the temperature range 318–338 K (well below its melting temperature). Real part of the conductivity spectra has been explained in terms of power law. The electrical properties of the thin films show a decrease in dc conductivity on incorporation of the Cu-nanoparticles.     

Fabrication, structure and luminescence properties of polycrystalline Tb-doped Lu2SiO5 films by Pechini sol–gel method

Tb³⁺-doped lutetium oxyorthosilicate (Tb:Lu₂SiO₅, LSO) films have been successfully fabricated on carefully cleaned silicon (1 1 1) substrates by Pechini sol–gel method combined with the spin-coating technique. X-ray diffraction (XRD), photoluminescence (PL) spectra and atomic force microscopy (AFM) were employed to characterize the resultant films. XRD patterns indicated that the films were crystallized into A-type LSO phase at 1000 °C, followed by a phase transition from A-type LSO to B-type LSO occurred at 1100 °C. The AFM observation revealed that the phosphor films were uniform and crack-free, consisting of closely packed grains with an average size of 200–300 nm. The PL spectra showed the characteristic emission ⁵D₄ → ⁷F_J (J = 3–6) for Tb³⁺, The lifetime of Tb³⁺ in Tb:LSO films was 2.33 ms. The effect of heat-treatment temperature on the luminescent properties was also investigated.     

Investigation of defect centres responsible for TL/OSL in MgAl2O4:Tb

Magnesium aluminate doped with Tb³⁺ (MgAl₂O₄:Tb³⁺) was prepared by combustion synthesis. Three thermoluminsence (TL) peaks at 120, 220 and 340 °C were observed. PL and TL emission spectrum shows that Tb³⁺ acts as the luminescent centre. Optically stimulated luminescence (OSL) was observed when stimulated by 470 nm blue light.Electron spin resonance (ESR) studies were carried out to identify the defect centres responsible for the TL and OSL processes in MgAl₂O₄:Tb³⁺. Two defect centres were identified in irradiated MgAl₂O₄:Tb³⁺ phosphor by ESR measurements which was carried out at room temperature and these were assigned to V and F⁺ centres. V centre (hole centre) is correlated to 120 and 220 °C TL peaks and F⁺ centre (electron centre), which acts as a recombination centre is correlated to 120, 220 and 340 °C.     

Preparation and luminescence properties of Tb doped ZrO2 and BaZrO3 phosphors

ZrO₂:Tb³⁺ and BaZrO₃:Tb³⁺ powders are prepared by combustion synthesis method and the samples were further heated to 500, 700 and 1000 °C to improve the crystallinity of the materials. The structure and morphology of materials have been examined by X-ray diffraction, Raman spectra and scanning electron microscopy. It is remarkable that all the samples of ZrO₂:Tb³⁺ and BaZrO₃:Tb³⁺ have similar morphology. These images exhibited homogeneous aggregates of varying shapes and sizes, which are composed of a large number of small cuboids and broken cuboids. The cuboids and broken cuboids size of all the samples are less than 0.5 μm. Photoluminescence for both materials increases with increase of temperature and found maximum for the samples heated to 1000 °C with 5 mole% doping of Tb³⁺ ions. Luminescence is almost double for the zirconia compared to that of barium-zirconate.     

Fabrication and luminescence properties of Al2O3:Tb3+ microspheres via a microwave solvothermal route

Al₂O₃:Tb³⁺ green phosphors were synthesized via a microwave solvothermal and thermal decomposition route, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra, and decay curves. XRD results indicate that Tb³⁺ doped samples are γ-Al₂O₃ after being calcined at 773 K. SEM results show that the particles of Al₂O₃:Tb³⁺ are hierarchically nanostructured microspheres assembled from nanosheets. The PL spectra indicate that the ⁵D₄→⁷F₅ (545 nm) electric dipole transition is the most intensive when excited at 235 nm. It is shown that 0.7 mol% of doping concentration of Tb³⁺ ions in γ-Al₂O₃:Tb³⁺ is optimum. According to Dexter's theory, the critical distance between Tb³⁺ ions for energy transfer was determined to be 18.4 Å. It is found that the curve followed the single-exponential decay. The excellent chromaticity coordinates of Al₂O₃:Tb³⁺ phosphors, as defined by the International Commission on Illumination (CIE), indicate that it is a good candidate for use in light display systems and optoelectronic devices.     

Photoluminescence spectra of rare earth doped CaGa2S4 single crystals

Six kind CaGa₂S₄ single crystals doped with different rare earth (RE) elements are grown by the horizontal Bridgman method, and their photoluminescence (PL) spectra are measured in the temperature range from 10 to 300 K. The PL spectra of Ce or Eu doped crystals have broad line shapes due to the phonon assisted 4f-5d transitions. On the other hand, those of Pr³⁺, Tb³⁺, Er³⁺ or Tm³⁺ doped samples show narrow ones owing to the 4f-4f transitions. The assignments of the electronic levels are made in reference to the reported data of RE 4f multiplets observed in same materials.     

Effect of Eu,Tb codoping on the luminescent properties of Y2O3 nanorods

Red-emitting Y₂O₃:Eu³⁺ and green-emitting Y₂O₃:Tb³⁺ and Y₂O₃:Eu³⁺, Tb³⁺ nanorods were synthesized by hydrothermal method. Their structure and micromorphology have been analyzed by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The photoluminescence (PL) property of Y₂O₃:Eu³⁺,Tb³⁺ phosphor was investigated. In the same host (Y₂O₃), upon excitation with ultraviolet (UV) irradiation, it is shown that there are strong emissions at around 610 and 545 nm corresponding to the forced electric dipole ⁵D₀-⁷F₂ transition of Eu³⁺ and ⁵D₄-⁷F₅ transition of Tb³⁺, respectively. Different qualities of Eu³⁺and Tb³⁺ ions are induced into the Y₂O₃ lattice. From the excitation spectrum, we speculate that there exists energy transfer from Tb³⁺ to Eu³⁺ ions .The emission color of powders reveals regular change in the separation of light emission. These powders can meet with the request of optical display material for different colors or can be potentially used as labels for biological molecules.     

Ionic liquid-assisted hydrothermal synthesis of dendrite-like NaY(MoO4)2:Tb phosphor

Micro-sized NaY(MoO₄)₂:Tb³⁺ phosphors with dendritic morphology was synthesized by a ionic liquid-assisted hydrothermal process. X-ray diffraction (XRD) indicated that the as-prepared product is pure tetragonal phase of NaY(MoO₄)₂. Field emission scanning electron microscopy (FE-SEM) images showed that the as-prepared NaY(MoO₄)₂:Tb³⁺ phosphors have dendritic morphology. The photoluminescent (PL) spectra displayed that the as-prepared NaY(MoO₄)₂:Tb³⁺ phosphors show a stronger green emission with main emission wavelength 545 nm corresponding to the ⁵D₄→⁷F₅ transition of Tb³⁺ ion, and the optimal Tb³⁺ doping concentration for obtaining maximum emission intensity was confirmed to be 10 mol%. Based on Van Uitert's and Dexter's models the electric dipole–dipole (D–D) interaction was confirmed to be responsible for the concentration quenching of ⁵D₄ fluorescence of Tb³⁺ in the NaY(MoO₄)₂:Tb³⁺ phosphors. The intrinsic radiative transition lifetime of ⁵D₄ level is found to be 0.703 ms.     

XPS analysis and luminescence properties of thin films deposited by the pulsed laser deposition technique

This paper presents the effect of substrate temperature and oxygen partial pressure on the photoluminescence (PL) intensity of the Gd₂O₂S:Tb^3?+? thin films that were grown by using pulsed laser deposition (PLD). The PL intensity increased with an increase in the oxygen partial pressure and substrate temperature. The thin film deposited at an oxygen pressure of 900 mTorr and substrate temperature of 900°C was found to be the best in terms of the PL intensity of the Gd₂O₂S:Tb^3?+? emission. The main emission peak due to the ⁵D₄–⁷F₅ transition of Tb was measured at a wavelength of 545 nm. The stability of these thin films under prolonged electron bombardment was tested with a combination of techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and Cathodoluminescence (CL) spectroscopy. It was shown that the main reason for the degradation in luminescence intensity under electron bombardment is the formation of a non-luminescent Gd₂O₃ layer, with small amounts of Gd₂S₃, on the surface.     

Facile synthesis and luminescence properties of uniform and monodisperse KY3F10:Ln3+ (Ln=Eu,Ce, Tb) nanospheres

Highly uniform and monodisperse KY₃F₁₀:Ln³⁺ (Ln=Eu, Ce, Tb) nanospheres, with an average diameter of 300 nm, have been successfully prepared through a simple template-free and surfactant-free stirring method under ambient conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectra were used to characterize the samples. The SEM images illustrate that these spheres were actually composed of randomly aggregated nanoparticles. The doped rare earth ions show their characteristic emission in the KY₃F₁₀ samples, i.e., Eu^{3+ 5}D₀–⁷F_J (J=1, 2, 3, 4), Tb^{3+ 5}D₄–⁷F_J (J=6, 5, 4, 3, 2) and Ce³⁺ 5d–4f transition emissions, respectively. An energy transfer phenomenon from Ce³⁺ to Tb³⁺ has been observed in KY₃F₁₀ nanospheres, and the energy transfer efficiency depends on the doping concentration of Tb³⁺ if the concentration of Ce³⁺ is fixed.