Preliminary study on singlet oxygen production using CeF3:Tb3+@SiO2-PpIX

Luminescent properties and singlet oxygen production using CeF₃:Tb³⁺-based nanoparticles modified with SiO₂ and protoporphyrin IX (PpIX) were studied. CeF₃:Tb³⁺ nanopowder was prepared via sol–gel route, with subsequent surface coating by SiO₂ layer and the conjugation with photosensitive PpIX molecules. Radioluminescence spectra suggest an energy transfer from Ce³⁺ to Tb³⁺ ions and from Tb³⁺ to molecules of PpIX photosensitizer. The energy transfer was confirmed by photoluminescence decay curves. Singlet oxygen production was detected using a reaction of ¹O₂ with 3’-(p-aminophenyl) fluorescein (APF) chemical probe after X-Ray excitation. Qualitative changes in time resolved photoluminescence spectra in the region of 520 nm indicate ¹O₂ generation. Studied nanocomposites may be good candidates for the application in X-ray induced photodynamic therapy.     

Luminescence properties and energy transfer investigations of BaAl2B2O7:Ce3+,Tb3+ phosphors

Ce³⁺ and Tb³⁺ co-doped BaAl₂B₂O₇ phosphors were synthesized by the solid-state method. X-ray diffraction (XRD) was used to characterize the phase structure. The photoluminescent properties of Ce³⁺ and Tb³⁺ co-doped BaAl₂B₂O₇ phosphors were investigated by using the photoluminescence emission and excitation spectra. Under the excitation of near ultraviolet (n-UV) light, BaAl₂B₂O₇:Ce³⁺,Tb³⁺ phosphors exhibited blue emission corresponding to the f–d transition of Ce³⁺ ions and green emission bands corresponding to the f–f transition of Tb³⁺ ions, respectively. Effective energy transfer occurred from Ce³⁺ to Tb³⁺ in BaAl₂B₂O₇ host due to the observed spectra overlap between the emission spectrum of Ce³⁺ ion and the excitation spectrum of Tb³⁺ ion. The energy transfer efficiency from Ce³⁺ ion to Tb³⁺ ion was also calculated to be 71%. Furthermore, the concentration quenching and critical distance of BaAl₂B₂O₇:Ce³⁺,Tb³⁺ phosphors were also discussed. The energy transfer from Ce³⁺ to Tb³⁺ in BaAl₂B₂O₇ host was demonstrated to be resonant type via a dipole–dipole interaction mechanism with the energy transfer critical distance of 16.13 Å.     

Green light emission by Ce3+ and Tb3+ co-doped Sr3MgSi2O8 phosphors for potential application in ultraviolet whitelight-emitting diodes

Sr₃MgSi₂O₈:Ce³⁺, Tb³⁺ phosphor samples were prepared using a solid-state reaction technique, and the photoluminescence properties and energy transfer were investigated. Effective energy transfer occurred in Ce³⁺/Tb³⁺ co-doped Sr₃MgSi₂O₈ phosphors. Co-doping of Ce³⁺ was found to enhance the emission intensity of Tb³⁺ to a certain extent by transferring energy to Tb³⁺. The Ce³⁺/Tb³⁺ energy transfer was thoroughly investigated through its emission/excitation spectra and photoluminescence decay behavior. The color emitted by Sr₃MgSi₂O₈:Ce³⁺, Tb³⁺ phosphors varied from blue to green and can be controlled by altering the concentration ratio of Ce³⁺ to Tb³⁺. These results indicate that Sr₃MgSi₂O₈:Ce³⁺, Tb³⁺ may be useful as a green-emitting phosphor for ultraviolet whitelight-emitting diodes.     

Luminescence properties and energy transfer in Ba2Y(BO3)2Cl:Ce3+,Tb3+ phosphors

Novel green-emitting Ba₂Y(BO₃)₂Cl:Ce³⁺,Tb³⁺ phosphors were synthesized by a solid-state method. X-ray diffraction and photoluminescence spectra were utilized to characterize the structures and luminescence properties of the as-synthesized phosphors, respectively. Ba₂Y(BO₃)₂Cl:Ce³⁺,Tb³⁺ phosphors exhibit blue and green emission bands under the excitation of near-ultraviolet light. An asymmetric blue emission originates from the Ce³⁺ ion, whereas the green emission originates from the Tb³⁺ ion. A spectral overlap is found between the emission band of the Ce³⁺ ion and the excitation band of the Tb³⁺ ion, which supports the occurrence of the energy transfer from the Ce³⁺ ion to the Tb³⁺ ion. Meanwhile, the energy transfer is thoroughly investigated by their photoluminescence decay behaviors. The energy-transfer efficiency from the Ce³⁺ ion to the Tb³⁺ ion is also calculated, and a possible mechanism is proposed.     

Multiplication of electronic excitations in nanophosphors Lu2O3:Eu and Lu2O3:Tb

Luminescence properties of Lu₂O₃:Eu³⁺ and Lu₂O₃:Tb³⁺ nanocrystalline powders with the particle size varying from 46 to 6 nm were studied under excitation by synchrotron radiation in the photon energy range (up to ∼22.5 eV) covering the region where the processes of multiplication of electronic excitation occur. It was found that the excitation spectra of Tb³⁺ emission from all Lu₂O₃:Tb³⁺ nanopowders have similar behavior, whereas the shape of the excitation spectra of Eu³⁺ emission from Lu₂O₃:Eu³⁺ nanopowders strongly depends on the particle size. The difference in the behavior of Lu₂O₃:Eu³⁺ and Lu₂O₃:Tb³⁺ nanophosphor systems was explained by different mechanisms of the energy transfer from the host to Eu³⁺ or Tb³⁺ ions (either the hole or electron recombination mechanism, respectively), which are differently influenced by losses of electronic excitations near the particle surface.     

In situ sol-gel composition of multicomponent hybrid precursor to hexagon-like Zn2SiO4:Tb microcrystalline phosphors with different silicate sources

Zn₂SiO₄ doped with Tb³⁺ were in situ synthesized by a modified sol-gel technology with the assembly hybrid precursor employed four different silicate sources, i.e. 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 micromorphological structures of hexagon-like with the dimension of 0.5-1.0 μm. The photoluminescent properties of Zn₂SiO₄:Tb³⁺ phosphors have been studied as a function of Tb³⁺ doping concentration. Cross-relaxation process between identical Tb³⁺ ions results in the quenching of the ⁵D₃ emission for high concentration sample.     

The energy transfer from Eu2+ to Tb3+ in calcium chlorapatite phosphor and its potential application in LEDs

Energy transfer from Eu²⁺ to Tb³⁺ was observed by investigating the optical properties from photoluminescence spectra and decay time curves in Tb³⁺ singly doped and Eu²⁺–Tb³⁺ co-doped calcium chlorapatite, Ca₅(PO₄)₃Cl (CPCl). It is dominated by the cooperation of a phonon-assisted energy transfer process and a non-radiative resonant energy transfer process caused by the exchange interaction. Eu²⁺–Tb³⁺ co-doped calcium chlorapatite phosphors in which Tb³⁺ can be efficiently excited by 400 nm are potential candidates for phosphor-converted LED.     

Emission analysis of Li6LuY(BO3)3:Tb3+,Dy3+ phosphors

In this paper, we present the synthesis and luminescence properties of Tb³⁺ and Dy³⁺-doped lithium lutetium yttrium borate (Li₆LuY(BO₃)₃) phosphors. We have adopted the well-known solid state reaction method for the synthesis of these phosphors. The emission intensities of the synthesized phosphors were found to reach their maximum, when doped by 1 mol% of Tb³⁺ and 3 mol% of Dy³⁺, beyond which emission intensities decrease due to concentration quenching. The homogeneous phase, crystalline structure and uniform morphology of the synthesized phosphors were confirmed by X-ray diffraction analysis (XRD) and Scanning electron microscopy (SEM). The X-ray and UV–VIS-induced luminescence, decay time and CIE chromaticity were investigated for the synthesized phosphors.The X-ray induced integrated light yield was measured to be 82% for Li₆LuY(BO₃)₃:Tb³⁺ (LLYBO) and 59% for Li₆LuY(BO₃)₃:Dy³⁺ of that of commercially available X-ray imaging material; Gd₂O₂S:Tb³⁺ (Gadox).LLYBO:Tb³⁺ phosphor displayed five major emission bands that correspond to ⁵D_j → ⁷F_j transitions. The 1931 Commission Internationale de l'Eclairage (CIE) chromaticity coordinates were also measured.     

Double emitting phosphor NaSr4(BO3)3:Ce, Tb for near-UV light-emitting diodes

Blue and green double emitting phosphor, Ce³⁺ and Tb³⁺ co-doped NaSr₄(BO₃)₃, was synthesized in a weak reducing atmosphere by a conventional high temperature solid-state reaction technique. For comparison, Ce³⁺ or Tb³⁺ singly doped NaSr₄(BO₃)₃ was also prepared. The emission and excitation spectra of all samples have been investigated. NaSr₄(BO₃)₃:Tb³⁺ excitation includes a strong absorption at about 240 nm and some weak sharp lines in near-ultraviolet (n-UV) spectral region. The excitation of Ce³⁺ and Tb³⁺ co-doped NaSr₄(BO₃)₃ shows a strong broad band absorption in the n-UV region from the contribution of Ce³⁺, which makes it suitable for excitation by a n-UV LED chip. The emission of NaSr₄(BO₃)₃:Ce³⁺,Tb³⁺ consists of a blue emission band from Ce³⁺ and a green emission from Tb³⁺ under the excitation of n-UV light. Energy transfer between Ce³⁺ and Tb³⁺ is also discussed, and the relative intensity of blue emission and green emission could be tuned by adjusting the concentration of Ce³⁺ and Tb³⁺. The phosphor NaSr₄(BO₃)₃:Ce³⁺,Tb³⁺ could be considered as a double emission phosphor for n-UV excited white light-emitting diodes.     

Synthesis and luminescence properties of Eu, Ce and Tb-activated Sr3La2(BO3)4 under UV excitation

The spectroscopic properties in UV-excitable range for the phosphors of Sr₃La₂(BO₃)₄:RE³⁺ (RE³⁺=Eu³⁺, Ce³⁺, Tb³⁺) were investigated. The phosphors were synthesized by conventional solid-state reactions. The photoluminescence (PL) spectra and commission international de I'Eclairage (CIE) coordinates of Sr₃La₂(BO₃)₄:RE³⁺ were investigated. The f-d transitions of Eu³⁺, Ce³⁺ and Tb³⁺ in the host lattices are assumed and corroborated. The PL and PL excitation (PLE) spectra indicate that the main emission wavelength of Sr₃La₂(BO₃)₄:Eu³⁺ is 611 nm, and Sr₃La₂(BO₃)₄:Ce³⁺ shows dominating emission peak at 425 nm, while Sr₃La₂(BO₃)₄:Tb³⁺ displays green emission at 487, 542, 582 and 620 nm. These phosphors were prepared by simple solid-state reaction at 1000 °C. There are lower reactive temperature and more convenient than commercial phosphors. The Sr₃La₂(BO₃)₄:Tb³⁺ applied to cold cathode fluorescent lamp was found to emit green light and have a major peak wavelength at around 542 nm. These phosphors may provide a new kind of luminescent materials under ultraviolet excitation.     

Ca8Mg(SiO4)4Cl2:Ce3+, Tb3+: A potential single-phased phosphor for white-light-emitting diodes

A single-phased white-light-emitting phosphor Ca₈Mg(SiO₄)₄Cl₂:Ce³⁺, Tb³⁺ (CMSC:Ce³⁺, Tb³⁺) is synthesized by a high temperature solid-state reaction method, and its photoluminescence properties are investigated. The obtained phosphor exhibits a strong excitation band between 250 and 410 nm, matching well with the dominant emission band of a UV light-emitting-diode (LED) chip. Energy transfer from Ce³⁺ to Tb³⁺ ions has been investigated and demonstrated to be a resonant type via a dipole–dipole mechanism. The energy transfer efficiency as well as the critical distance is also estimated. Furthermore, the phosphors can generate light from yellow-green through white and eventually to blue by properly tuning the relative ratio of Ce³⁺ to Tb³⁺ ions grounded on the principle of energy transfer. The results show that this phosphor has potential applications as a single-phased phosphor for UV white-light LEDs.     

Luminescence of CaWO4:Pr3+ and CaWO4:Tb3+ at ambient and high hydrostatic pressures

Photoluminescence spectra of CaWO₄ doped with Pr³⁺ and Tb³⁺ obtained at high hydrostatic pressures up to 315 kbar applied in a diamond anvil cell (DAC) are presented. The intensities of the luminescence from the ³P₀ state of Pr³⁺ and from the ⁵D₃ state of Tb³⁺ decreased with increasing pressure. At pressures greater than 50 kbar, the ¹D₂ → ³H_J transitions in Pr³⁺ and the ⁵D₄ → ⁷F_J transitions in Tb³⁺ dominated the spectra. At pressures greater than 100 kbar, only emissions from the lower excited states were observed. At pressures greater than 150 kbar, luminescence from the ¹D₂ and ⁵D₄ states also decreased with increasing pressure, and at a pressure of 315 kbar for CaWO₄:Pr³⁺ and 190 kbar for CaWO₄:Tb³⁺, the emissions related to the Pr³⁺ and Tb³⁺ were quenched. These effects were related to the influence of impurity trapped excitons (ITEs) on the efficiency of the f–f emission in the Pr³⁺ and Tb³⁺ ions. Analysis of the emission spectra collected at different pressures allowed the energies of the ground states of the Pr³⁺ and Tb³⁺ ions with respect to the band edges of the CaWO₄ host to be estimated.     

Luminescence and energy transfer of white-light emitting CaAl2SiO6:Ce3+, Tb3+ phosphors

A novel white-light emitting CaAl₂SiO₆: Ce³⁺, Tb³⁺ phosphor has been prepared by a sol–gel method. X-ray diffractometry and spectrofluorometry were used to characterize structural and optical properties of the samples. The results indicate that the crystal structure of the phosphor is a single phase of CaAl₂SiO₆. The excitation band of the phosphor covers a wide region from 240 nm to 380 nm. CaAl₂SiO₆: Ce³⁺, Tb³⁺ phosphors show four emission bands: one at 400 nm for Ce³⁺ and three at 487 nm, 543 nm and 585 nm for Tb³⁺. With appropriate tuning of Tb³⁺ content, white light with different hues can be achieved under UV radiation. The energy transfer mechanism from Ce³⁺ to Tb³⁺ in CaAl₂SiO₆ host was demonstrated to be dipole–dipole interaction.     

OSL, RL and TL characterization of rare-earth ion doped K2YF5: Application in dosimetry

Optically stimulated luminescence (OSL) properties of K₂YF₅ crystals singly doped with different concentrations of Tb³⁺ ions and doubly doped with Tb³⁺ and Ce³⁺ or Tb³⁺ and Dy³⁺ have been investigated for the first time. Radioluminescence spectra and OSL efficiency for stimulation with different wavelengths of light have been analyzed for each compound. Also, dosimetric characteristics of the most efficient composition, namely K₂YF₅:1 at.% Tb³⁺, have been studied. Finally, the OSL signal peculiarities for K₂YF₅:1 at.% Tb³⁺ have been compared to those of a commercial Al₂O₃:C dosimeter.     

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.     

Eu/Tb ions co-doped white light luminescence Y2O3 phosphors

Y₂O₃:Eu³⁺, Tb³⁺ phosphors with white emission are prepared with different doping concentration of Eu³⁺ and Tb³⁺ ions and synthesizing temperatures from 750 to 950 °C by the co-precipitation method. The resulted phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The results of XRD indicate that the crystallinity of the synthesized samples increases with enhancing the firing temperature. The photoluminescence spectra indicate the Eu³⁺ and Tb³⁺ co-doped Y₂O₃ phosphors show five main emission peaks: three at 590, 611 and 629 nm originate from Eu³⁺ and two at 481 and 541 nm originate from Tb³⁺, under excitation of 250-320 nm irradition. The white light luminescence color could be changed by varying the excitation wavelength. Different concentrations of Eu³⁺ and Tb³⁺ ions were induced into the Y₂O₃ lattice and the energy transfer from Tb³⁺→Eu³⁺ ions in these phosphors was found. The Commission International de l’Eclairage (CIE) chromaticity shows that the Y₂O₃:Eu³⁺, Tb³⁺ phosphors can obtain an intense white emission.     

Luminescence enhancement by energy transfer from Ce ions in Ba1.6Ca0.4P2O7:Ce:Tb phosphor

The optical properties of Ba_1.6Ca_0.4P₂O₇ doped with Ce³⁺ and Tb³⁺ are investigated. Under excitation at 280 nm the emission spectrum of Ba_1.6Ca_0.4P₂O₇:Ce³⁺ consists of a peak at 370 nm and a shoulder at the longer wavelength side. The emission spectra of Ba_1.6Ca_0.4P₂O₇:Tb³⁺ shows the well-known emission lines due to ⁵D₄-⁷F_J transitions of Tb³⁺. The green emissions of Tb³⁺ ions are enhanced upon UV excitation through energy transfer from Ce³⁺ to Tb³⁺ ions. The efficiency of such an energy transfer is estimated based on spectroscopic data. The dependence of photoluminescence (PL) intensities of Ce³⁺ and Tb³⁺ emissions on Ce³⁺ or Tb³⁺ concentrations in the systems (Ba_1.6Ca_0.4P₂O₇:0.04Ce³⁺,xTb³⁺ and Ba_1.6Ca_0.4P₂O₇:xCe³⁺,0.04Tb³⁺) and the temperature dependence of PL emission spectra of Ba_1.6Ca_0.4P₂O₇:0.06Ce³⁺,0.04Tb³⁺ is also investigated.     

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.     

Preparation and characterization of Tb and Tb(sal)3·nH2O doped PC:PMMA blend

Tb doped polycarbonate:poly(methyl methacrylate) (Tb-PC:PMMA) blend was prepared with varying proportions of PC and PMMA. Thermal and spectroscopic properties of the doped polymer have been investigated employing Fourier Transform Infrared (FTIR) absorption and differential scanning calorimetric (DSC) techniques. PC:PMMA blend (with 10 wt% PC and 90 wt% PMMA) shows better miscibility. Optical properties of the dopant Tb³⁺ ions have been investigated using UV-vis absorption and fluorescence excited by 355 nm radiation. It is seen that luminescence intensity of Tb³⁺ ion depends on PC:PMMA ratio and on Tb³⁺ ion concentration. Concentration quenching is seen for TbCl₃·6H₂O concentration larger than 4 wt%. Addition of salicylic acid to the polymer blend increases the luminescence from Tb³⁺ ions. Luminescence decay curve analysis affirms the non-radiative energy transfer from salicylic acid to Tb³⁺ ions, which is identified as the reason behind this enhancement.     

Optical and fluorescent properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> sol–gel planar waveguides containing Tb<Superscript>3+</Superscript> doped nanocrystals

Terbium doped Y₂O₃ planar waveguides were fabricated by sol–gel process and dip-coating using yttrium acetate as precursor. Two different doping modes were compared, i.e. introduction in the sol of dispersed Tb³⁺ions from dissolved Tb(NO₃)₃, or of nanoparticles of Tb₂O₃ or [Y₂O₃:50% Tb] from an alcoholic suspension. The chemical and nanostructural properties were analyzed by infrared spectroscopy, transmission electron microscopy and X-ray diffraction. The Tb³⁺ fluorescence properties were studied as a function of temperature and atmosphere of the thermal treatments, and of the Tb³⁺ concentration. The fluorescence properties are discussed in relation to the quenching mechanisms induced by Tb⁴⁺ transformation, residual OH groups, and crystallites size and structure. Optical propagation losses of the Tb doped Y₂O₃ planar waveguides related to the doping modes and Tb³⁺ concentration are presented. Doping sol–gel films by nanoparticles is shown to be a valuable alternative to the conventional doping from dissolved terbium salt. PACS 81.21.Fw; 84.40.Az; 78.67.Bf