Synthesis and luminescence investigation of RE (Eu, Tb and Ce)-doped lithium silicate (Li2SiO3)

Synthesis and photoluminescence (PL) investigations of lithium metasilicate doped with Eu³⁺, Tb³⁺ and Ce³⁺ were carried out. PL spectra of Eu-doped sample showed peaks corresponding to the ⁵D₀→⁷F_j (j=1, 2, 3 and 4) transitions under ultraviolet excitation. Strong red emission coming from the hypersensitive ⁵D₀→⁷F₂ transition of Eu³⁺ ion suggested the presence of the dopant ion in structurally disordered environment. Tb³⁺-doped silicate sample showed blue-green emission corresponding to the ⁵D₄→⁷F_j (j=6, 5 and 4) transitions. Ce-doped sample under excitation from UV, showed a broad emission band in the region 350-370 nm with shoulders around 410 nm. The fluorescence lifetimes of Eu³⁺ and Tb³⁺ ions were found out to be 790 and 600 μs, respectively. For Ce³⁺, the lifetime was of the order of 45 ns. PL spectra of the europium- and terbium-doped samples were compared with commercial red (Y₂O₃:Eu³⁺) and green (LaPO₄:Tb³⁺) phosphors, respectively. It was found that the emission from the doped silicate sample was 37% of the commercial phosphor in case of the Tb-doped sample and 8% of the commercial phosphor in case of the Eu-doped sample.     

VUV-UV luminescence of magnetoplumbite: (Sr0.96−xBa0.04)Al12−yMgyO19:Tbx

The title compounds (Sr_0.96−xBa_0.04)Al_12−yMg_yO₁₉:Tb_x (0<x<0.4; 0<y<0.18) are single-phase magnetoplumbite determined by X-ray powder diffraction analysis. The characteristic emission lines of ⁵D₃→⁷F_j (j=2, 3, 4, 5) and ⁵D₄→⁷F_j (j=4, 5, 6) of Tb³⁺ are recorded under the VUV excitation. The intensive luminescence mainly comes from ⁵D₃→⁷F_j transition when the concentration of Tb³⁺ is low. However, when the concentration of Tb³⁺ starts to increase from very low concentration, ⁵D₄→⁷F_j transition is becoming dominant. Three broad excitation bands at 165, 193 and 233 nm have been observed. The band at 165 nm originates from the overlap between the host absorption and the charge transfer of Tb³⁺-O²⁻. The other two broad bands are the first spin-allowed and the spin-forbidden of 4f-5d transition, respectively. The experimental observation of the 4f-5d transition of Tb³⁺ is consistent well with the theoretical expectations.     

Photoluminescence properties and effects of dopant concentration in Bi2ZnB2O7:Tb phosphor

A novel green phosphor, Tb³⁺ doped Bi₂ZnB₂O₇ was synthesized by conventional solid state reaction method. The phase of synthesized materials was determined using the XRD, DTA/TG and FTIR. The photoluminescence characteristics were investigated using spectrofluorometer at room temperature. Bi₂ZnB₂O₇:Tb³⁺ phosphors excited by 270 nm and 485 nm wavelengths. The emission spectra were composed of three bands, in which the dominated emission of green luminescence Bi₂ZnB₂O₇:Tb³⁺ attributed to the transition ⁵D₄ → ⁷F₅ is centered at 546 nm. The dependence of the emission intensity on the Tb³⁺ concentration for the Bi_2−xTb_xZnB₂O₇ (0.01 ≤ x ≤ 0.15) was studied and observed that the optimum concentration of Tb³⁺ in phosphor was 13 mol% for the highest emission intensity at 546 nm.     

Emission analysis of Tb:MgAl2O4 powder phosphor

This paper reports the emission analysis of green-emitting Tb³⁺-doped MgAl₂O₄ phosphors. Uniformity of the phase of the Tb³⁺-doped MgAl₂O₄ phosphor has been checked by X-ray diffraction (XRD) technique and show common bands existing in the results of Fourier transform infrared (FT-IR). This phosphor exhibits weak blue, orange emissions and a strong emission at λ_exci=350 nm. The blue and green-orange emissions are ascribed to ⁵D₃→⁷F_J and ⁵D₄→⁷F_J (where J=3-6) transitions of Tb³⁺ ions, respectively. These phosphors have shown a strong, more prominent green emission from ⁵D₄→⁷F₅ at 543 nm. The results have indicated that MgAl₂O₄:Tb³⁺ could be a potential candidate as agreen-emitting powder phosphor.     

White-light long-lasting phosphorescence from Tb-activated Y2O2S phosphor

The white-light long-lasting phosphors Y₂O₂S:Tb³⁺, Sr²⁺ or/and Zr⁴⁺ were prepared and studied. The white-light afterglow emission after the irradiation with 254 nm UV are composed of the blue light emission and the yellowish-green light emission, originating from the transitions of ⁵D₃→⁷F₅, ⁵D₄→⁷F₅ in Tb³⁺ when the Tb³⁺ concentration is not higher than 0.3 at%. The codoped Sr²⁺ and Zr⁴⁺ ions act as trap-creating ions. The afterglow can last over 21 min in the dark for Y₂O₂S:Tb³⁺0.3%, Sr²⁺4%, Zr⁴⁺4% after irradiation by 254 nm ultraviolet light. Y₂O₂S:Tb³⁺ may be a promising material for the development of white-light long-lasting phosphor since the Tb³⁺ has a high luminescent efficiency and the dominant excitation band of 4f →5d is located at 220-300 nm.     

Rare earth doped lithium titanate (Li2TiO3) for potential phosphor applications

Lithium titanate ceramics doped with three rare earth (RE) ions namely Eu³⁺, Dy³⁺ and Tb³⁺ were synthesized and their photoluminescence (PL) properties were investigated. PL spectra of Eu doped sample showed peaks corresponding to the ⁵D₀→⁷F_j (j=0, 1, 2, 3 and 4) transitions under 230 nm excitation. Strong red emission coming from the hypersensitive ⁵D₀→⁷F₂ transition of Eu³⁺ ion suggested the presence of the dopant ion in a highly asymmetric environment. Dy doped samples showed the Dy³⁺ emission characteristic due to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions. Their relative intensity ratios also suggested the presence of asymmetric environment around the metal ion. In case of the Tb³⁺ doped sample blue-green emission corresponding to the ⁵D₄→⁷F_j (j=6, 5 and 4) transitions was seen. The fluorescence lifetimes of Eu³⁺, Dy³⁺ and Tb³⁺ ions were found to be 645, 900 and 740 μs, respectively. PL intensity of the individual rare earth doped samples was compared with commercial red and green phosphors. It was found that the emission from Eu doped titanate sample was 46% of the commercial red phosphor and in case of the Tb samples it was 30% when excited at 230 nm. However, the synthesized Eu doped titanate sample showed better color purity as compared to the commercial phosphor. The titanate host was doped with all the three rare earths to get white light emission from the system. The individual rare earth ion content was optimized so as to get a near white light emission. The color coordinates of the triple doped systems were evaluated and plotted on the CIE x–y diagram. Our results suggest that lithium titanate has enough potential to be a phosphor material.     

Upconversion luminescence in Yb/Tb-codoped monodisperse NaYF4 nanocrystals

Upconversion (UC) luminescence in monodisperse NaYF₄:Yb³⁺/Tb³⁺ nanocrystals was observed under diode laser excitation of 970 nm, which were synthesized by a hydrothermal method. UC emissions at 380, 413, 436 nm and at 488, 542, 584, 620 nm arise from transitions ⁵D₃(⁵G₆) → ⁷F_J(J = 6, 5, 4) and ⁵D₄ → ⁷F_J(J = 6, 5, 4, 3) of Tb³⁺ ions, respectively. UC mechanisms are proposed based on spectral, kinetic, decay time measurements, and pump power dependence analyses. Blue, green and red emissions originate from the same long-lived (milliseconds) upper ⁵D₄ state, which promises the potential applications of these monodisperse Yb³⁺/Tb³⁺-codoped NaYF₄ nanocrystals in the field of photonics, lasers and biomedicine.     

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.     

Sol-gel preparation and photoluminescence property of YBO3:Eu/Tb nanocrystalline thin films

YBO₃:Eu³⁺/Tb³⁺ nanocrystalline thin films were successfully deposited onto quartz glass substrates by Pechini sol-gel dip-coating method, using rare-earth nitrates and boric acid as starting materials. The crystal structure, morphology, chemical composition and photoluminescence property of the films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and fluorescence spectrophotometer. The results of XRD, AFM, XPS and FTIR revealed that the films were composed of spherical YBO₃:Eu³⁺/Tb³⁺ nanocrystals with average grain size of 80 nm. The YBO₃:Eu³⁺ film exhibited strong orange emission at 595 nm and red emission at 615 nm, which were, respectively ascribed to the (⁵D₀→⁷F₁) and (⁵D₀→⁷F₂) transitions of Eu³⁺. The YBO₃:Tb³⁺ film showed dominant green emission at 545 nm due to the ⁵D₄-⁷F₅ transition of Tb³⁺.     

D3→FJ emission of Tb doped sol–gel silica

Amorphous silica samples doped with 0.1 and 1 mol% of terbium (Tb) were synthesized by the sol–gel method. In addition to the green light associated with ⁵D₄→⁷F_J transitions of Tb³⁺, the sample containing 0.1 mol% also emitted blue light as a result of ⁵D₃→⁷F_J transitions during photoluminescence (PL) measurements. As a result of concentration quenching this blue emission was not observed for the samples doped with the higher concentration (1 mol%). However the blue ⁵D₃ →⁷F_J emission was observed in the 1 mol% doped samples during cathodoluminescence (CL) measurements. Since a rough calculation indicated that the excitation rate in the CL system where the blue emission is observed may be similar to a laser PL system under conditions where the blue emission is not observed, the difference is attributed to the nature of the excitation sources. It is suggested that during the CL excitation incident electrons can reduce non-luminescent Tb⁴⁺ ions in the silica, substituting for Si⁴⁺ ions, to the excited (Tb³⁺)? state and that these are responsible for the blue emission, which does not occur during PL excitation.     

Synthesis, microstructure and photoluminescence of Eu/Tb activated Y2SiO5 nanophosphors by new silicate sources

Y_2−xTb_xSiO₅ and Y_2−xEu_xSiO₅ nanophosphors with seven different kinds of silicate sources were synthesized by sol-gel method. The structures have been investigated to be composed of nanometer-size grains of 30-60 nm through X-ray diffraction (XRD) and scanning electron microscopy (SEM) was used to compare the different morphology of patterns from seven different silicon sources. The photoluminescence of Y_2−xTb_xSiO₅ was investigated as a function of silicate sources and the results revealed that these nanometer materials showed the characteristic emission ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) of Tb ions. The characteristic emission ⁵D₀ → ⁷F_J (J = 1, 2, 4) of Eu ions was also found in the materials of Y_2−xEu_xSiO₅.     

Eu photoluminescence enhancement due to thermal energy transfer in Eu2O3-doped SiO2-B2O3-PbO2 glasses system

In this work, Eu³⁺-doped lead borosilicate glasses (SiO₂-B₂O₃-PbO₂) synthesized by fusion method had their optical properties investigated as a function of temperature. Atomic Force Microscopy images obtained for a glass matrix annealed at 350 and 500 °C show a precipitated crystalline phase with sizes 11 and 21 nm, respectively. Besides, as the temperature increases from 350 to 300 K a strong Eu³⁺ photoluminescence (PL) enhancement takes place. This anomalous feature is attributed to the thermally activated carrier transfer process from nanocrystals and charged intrinsic defects states to Eu³⁺ energy levels. In addition, the PL peaks in this temperature range were assigned to the Eu³⁺ transitions ⁵D₀→⁷F₂, at 612 nm, ⁵D₀→⁷F₁, at 595 nm, and ⁵D₀→⁷F₀, at 585 nm. It was also observed that the ⁵D₀→⁷F₃ and ⁵D₀→⁷F₄ PL bands at 655 and 700 nm, respectively, show a continuous decrease in intensity as the temperature increases.     

Dependence of photoluminescent properties of cubic Y2O3:Tb nanocrystals on particle size and temperature

Temperature-dependent spectral properties in the cubic Y₂O₃:Tb³⁺ nanocrystals (NCs, 10-70 nm) under 488 nm excitation were studied and compared to that in the bulk. In NCs, emission lines assigned to the ⁵D₄-⁷F_J (J=1-6) transitions of Tb³⁺ ions and a broad band originated from oxygen defects were observed. As a function of temperature, two intensity maximums of the ⁵D₄-Σ⁷F_J transitions appeared in the NCs, at ∼250 and ∼500 K, while in the bulk only one maximum appeared at ∼250 K. The relative intensity of the maximum at ∼500 K to that at ∼250 K increased with decreasing particle size. The intensity maximum of the band emissions that came from the oxygen defects appeared in the range of 500-600 K. The appearance of intensity maximum as a function of temperature was attributed to the rivalry between thermal quenching process and phonon-assisted excitation. The appearance of two maxima in the NCs was attributed to the luminescence contributed by different Tb³⁺ centers, the internal and the surface. The emission for the surface Eu³⁺ centers has higher quenching temperature in contrast to that for the internal centers.     

Investigation on luminescence and energy transfer in Tb-doped lead telluroborate glasses

This work reports on the visible luminescence properties and energy transfer processes responsible for non-exponential nature of the decay curves and also quenching of luminescence intensity of the ⁵D₃→⁷F_J transitions of Tb³⁺ ions in lead telluroborate (PTB) glasses containing different Tb³⁺ concentrations. The XRD and FT-IR spectra were measured to study the glassy nature and composition of the prepared glasses. The radiative properties are determined using the Judd-Ofelt theory to judge the suitability of studied glasses as practical photonic material. These parameters suggest that the PTBTb20 glass has the potential to produce intense green emission (544 nm) through the ⁵D₄→⁷F₅ transition.     

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.     

A white light emitting phosphor Sr1.5Ca0.5SiO4:Eu, Tb, Eu for LED-based near-UV chip: Preparation, characterization and luminescent mechanism

In this work, we report preparation, characterization and luminescent mechanism of a phosphor Sr_1.5Ca_0.5SiO₄:Eu³⁺,Tb³⁺,Eu²⁺ (SCS:ETE) for white-light emitting diode (W-LED)-based near-UV chip. Co-doped rare earth cations Eu³⁺, Tb³⁺ and Eu²⁺ as aggregated luminescent centers within the orthosilicate host in a controlled manner resulted in the white-light phosphors with tunable emission properties. Under the excitation of near-UV light (394 nm), the emission spectra of these phosphors exhibited three emission bands: one broad band in the blue area, a second band with sharp lines peaked in green (about 548 nm) and the third band in the orange-red region (588-720 nm). These bands originated from Eu²⁺ 5d→4f, Tb³⁺⁵D₄→⁷F_J and Eu³⁺⁵D₀→⁷F_J transitions, respectively, with comparable intensities, which in return resulted in white light emission. With anincrease of Tb³⁺ content, both broad Eu²⁺ emission and sharp Eu³⁺ emission increase. The former may be understood by the reduction mechanism due to the charge transfer process from Eu³⁺ to Tb³⁺, whereas the latter is attributed to the energy transfer process from Eu²⁺ to Tb³⁺. Tunable white-light emission resulted from the system of SCS:ETE as a result of the competition between these two processes when the Tb³⁺ concentration varies. It was found that the nominal composition Sr_1.5Ca_0.5SiO₄:1.0%Eu³⁺, 0.07%Tb³⁺ is the optimal composition for single-phased white-light phosphor. The CIE chromaticity calculation demonstrated its potential as white LED-based near-UV chip.     

Luminescence properties of Ce and Tb co-activated ZnAl2O4 phosphor

In this study, a solution combustion method was used to prepare green emitting Ce³⁺–Tb³⁺ co-activated ZnAl₂O₄ phosphor. The samples were annealed at 700 °C in air or hydrogen atmosphere to improve their crystallinity and optical properties. X-ray diffraction study confirmed that both as-prepared and post-preparation annealed samples crystallized in the well known cubic spinel structure of ZnAl₂O₄. An agglomeration of irregular platelet-like particles whose surfaces were encrusted with smaller spheroidal particles was confirmed by scanning electron microscopy (SEM). The fluorescence data collected from the annealed samples with different concentrations of Ce³⁺ and Tb³⁺ show the enhanced green emission at 543 nm associated with ⁵D₄→⁷F₅ transitions of Tb³⁺. The enhancement was attributed to energy transfer from Ce³⁺ to Tb³⁺. Possible mechanism of energy transfer via a down conversion process is discussed. Furthermore, cathodoluminescence (CL) intensity degradation of this phosphor was also investigated and the degradation data suggest that the material was chemically stable and the CL intensity was also stable after 10 h of irradiation by a beam of high energy electrons.     

Solvothermal synthesis and luminescence properties of Tb-doped gadolinium aluminum garnet

Different concentrations of Tb³⁺ ion-doped gadolinium aluminum garnet (GAG) nanophosphors have been synthesized by solvothermal reaction method and sintered at 1300 °C. The XRD patterns confirm that the GAG phosphors sintered at 1300 °C have a garnet structure with single cubic phase. The calculated crystallite size is about 92 nm. The SEM images of the phosphors show the spherical morphology agglomerated with many small particles. The luminescence properties of these phosphors have been carried out by the emission and excitation spectra along with lifetime measurements. The excitation spectra of GAG:Tb³⁺ phosphors consist of three broad bands due to the 4f⁸→4f⁷5d¹ transition and some sharp peaks due to the 4f⁸→4f⁸ transition. The emission spectra of the phosphors reveal two colors, such as blue due to ⁵D₃→⁷F_J transitions and green due to the ⁵D₄→⁷F_J transitions. The dynamics of the phosphors have been investigated by decay curves and the cross-relaxation process and is observed at 0.5 mol% Tb³⁺ concentration.     

New promising phosphors Ba3InB9O18 activated by Eu/Tb

Borate Ba₃InB₉O₁₈ (BIBO) has been adopted as a host material for phosphors for the first time. Lanthanide ions (Eu³⁺/Tb³⁺)-doped BIBO phosphors have been synthesized by solid-state reaction and luminescent properties investigated under ultravoilet (UV) excitation. For red phosphor BIBO:Eu, dominant emission peaking at 590 nm was attributed to ⁵D₀→⁷F₁ transition of Eu³⁺, which confirmed that the local site of Eu³⁺ occupied by In³⁺ ion in BIBO crystal lattice is at inversion symmetry center. Optimum Eu³⁺ concentration of BIBO:Eu under UV excitation with 227 nm wavelength is around 40%. The green phosphor BIBO:Tb showed bright green emission at 550 with 232 nm light excited and optimal of Tb³⁺ concentration measured in BIBO is about 8%. The corresponding luminescence mechanisms of Ln-doped BIBO (Ln=Eu³⁺/Tb³⁺) were analyzed. The luminescent intensity of Tb³⁺ can be significantly improved by co-doping of Bi³⁺ in the BIBO:Tb lattice. The likely reason was proposed in terms of the different interactions of the host lattice with these ions, and of these ions with each other.     

Synthesis, photoluminescence, thermoluminescence and dosimetry properties of novel phosphor Zn(BO2)2:Tb

Polycrystalline powder samples of terbium doped Zn(BO₂)₂ phosphors were prepared by solid state reaction in the thermal carbon reducing atmosphere at high temperature. The photoluminescence (PL), three-dimensional (3D) TL emission spectrum and dosimetric characteristics following ⁶⁰Co gamma-rays irradiation were studied. Characteristic emission bands of Tb³⁺ at about 490, 543, 584 and 620 nm, attributed to the ⁵D₄→⁷F_J (J=3, 4, 5, 6) transitions of Tb³⁺ ions, were observed in the TL and PL emission spectrum. No emission from Tb⁴⁺ ions was observed in the TL emission spectrum. The TL-dose response of the powder samples Zn(BO₂)₂:Tb to ⁶⁰Co gamma-rays radiation in the dose range from 1 to 100 Gy for clinical dose levels was almost linear. The experiment results showed that Zn(BO₂)₂:Tb has potential use as the materials of gamma-rays thermoluminescence dosimeter (TLD) for clinical dosimetry.