Co-existence phenomenon of Ce3+/Ce4+ and Tb3+ in Ce/Tb co-doped Zn2(BO3)(OH)0.75F0.25 phosphor: Luminescence and energy transfer

A serials of Zn₂(BO₃)(OH)_0.75F_0.25 (ZBF), Tb³⁺, Ce^3+/4+ single-doped ZBF and Tb³⁺/Ce^3+/4+ co-doped ZBF novel phosphors with belt-like morphology were obtained through hydrothermal reaction without any surfactant. The obtained samples were characterized by XRD, SEM, EDS, TEM, TGA, XPS, DR, PL, and DT. The TGA curve shows that the phosphor is thermal stability. XPS results show that Tb³⁺ is present in the Tb-doped phosphor, and the Ce³⁺/Ce⁴⁺ mixed valence is present in the Ce-doped phosphor. The PL results indicate that ZBF host material and ZBH:Ce^3+/4+ can emit blue light, ZBF:Tb³⁺ can emit green light. Compared with the Tb³⁺ single doped phosphor, the Tb³⁺/Ce^3+/4+ co-doped phosphors shown stronger emission and shorter decay time, which is attributed to the effective energy transfer from the Ce^3+/4+ to Tb³⁺ ions.     

Luminescence properties and energy transfer of co-doped Ba<Subscript>3</Subscript>GdNa(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>F:Ce<Superscript>3+</Superscript>,Tb<Superscript>3+</Superscript> green-emitting phosphors

Phase pure Ce³⁺ and Tb³⁺ singly doped and Ce³⁺/Tb³⁺ co-doped Ba₃GdNa(PO₄)₃F samples have been synthesized via the high temperature solid-state reaction. The crystal structures, photoluminescence properties, fluorescence lifetimes, thermal properties and energy transfer of Ba₃GdNa(PO₄)₃F:Ce³⁺,Tb³⁺ were systematically investigated. Rietveld structure refinement indicates that Ba₃GdNa(PO₄)₃F crystallizes in a hexagonal crystal system with the space group P-6. For the co-doped Ba₃GdNa(PO₄)₃F:Ce³⁺,Tb³⁺ samples, the emission color can be tuned from blue to green by varying the doping concentration of the Tb³⁺ ions. The intense green emission was realized in the Ba₃GdNa(PO₄)₃F:Ce³⁺,Tb³⁺ phosphors on the basis of the highly efficient energy transfer from Ce³⁺ to Tb³⁺. Also the energy transfer mechanism has been confirmed to be quadrupole–quadrupole interaction, which can be validated via the agreement of critical distances obtained from the concentration quenching (13.84 Å). These results show that the developed phosphors may possess potential applications in near-ultraviolet pumped white light-emitting diodes.     

Luminescent properties of single-phase Ba<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>:Tb<Superscript>3+</Superscript>, R (R = Eu<Superscript>2+</Superscript>, Ce<Superscript>3+</Superscript>) phosphors for white LED

The Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) phosphors were synthesized by use of a co-precipitation method. Crystal phase, excitation and emission spectra of sample phosphors are analyzed by means of XRD and FL, respectively. The emission spectra of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors exhibit four linear peaks attributed to the ⁵D₄?→?⁷F_J (J?=?6–3) transition of Tb³⁺ while four broad emission bands are observed in the emission spectra of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The effects of Eu²⁺ concentration on the luminescent properties of Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) are studied. Ce³⁺ affects the luminescent properties of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors just as the sensitizer. However, Eu²⁺ is considered both as the sensitizer and the activator in Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The chromaticity coordinates of Eu²⁺ and Tb³⁺ co-doped phosphors gather around the white light field with the CCT approximate to 5000 K, indicating that the luminescent property of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors may approach to a desired level needed for white LED application.     

Luminescence properties and energy transfer of a novel bluish-green tunable NaBa4(BO3)3:Ce3+, Tb3+ phosphor

A series of single-phased emission tunable NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ phosphors were synthesized by solid-state reaction. The crystal structure, photoluminescence properties, concentration quenching and energy transfer of NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ were systematically investigated. The wavelength-tunable bluish-green light can be realized by coupling the emission bands centered at 425 and 543 nm ascribed to the contribution from Ce³⁺ and Tb³⁺, respectively. The energy transfer from Ce³⁺ to Tb³⁺ in NaBa₄(BO₃)₃ host was studied and demonstrated to be a resonant type via a dipole–dipole interaction mechanism. The energy transfer efficiency (Ce³⁺ → Tb³⁺) obtained by decay curves was consistent with the result calculated by the emission intensity, which gradually increased from 0% to 84.5% by increasing the Tb³⁺ doping content from 0 to 0.45. The results indicate that the NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ phosphors have potential applications as an ultraviolet-convertible phosphor due to its effective excitation in the ultraviolet rang.     

Synthesis and luminescence of BiPO4:Ln3+ (Ln = Ce3+, Tb3+) phosphors

BiPO₄:Ce³⁺ and BiPO₄:(Ce³⁺, Tb³⁺) powders were synthesized by the method of precipitation. The X-ray diffraction patterns show that BiPO₄:Ce³⁺ and BiPO₄:(Ce³⁺, Tb³⁺) samples have pure hexagonal phases. The transmission electron microscopy results show that the synthesized samples are nanoparticles. Ethylene glycol plays an important role in the formation of nanoparticles. The excitation spectrum of BiPO₄:Ce³⁺ sample shows the transition from the ground ² F _5/2 state to the excited 5d states of the Ce³⁺ ions. The emission spectrum exhibits a strong band centered at 352 nm originating from the 5d → 4f transitions of the Ce³⁺ ions. The emission spectrum of the BiPO₄:(Ce³⁺, Tb³⁺) sample contains both a weak emission band of the Ce³⁺ ions and strong green emission bands of the Tb³⁺ ions. The excitation and emission spectra show that there are energy transfers between Ce³⁺ and Tb³⁺ ions in the BiPO₄:(Ce³⁺, Tb³⁺) sample. The energy transfers between Ce³⁺ and Tb³⁺ ions improve the emission efficiency of BiPO₄:(Ce³⁺, Tb³⁺) sample.     

The luminescent enhancement of LaPO4:Ce3+,Tb3+ nano phosphors by radial aggregation

The rare earth nano phosphors can meet the challenging demand for new functional devices but their luminescence is always poor. Here we report on a simple method to prepare uniform LaPO₄:Ce³⁺,Tb³⁺ sphere-like nano aggregates from the precipitated nano phosphor crystallites without using any additive. The spontaneous aggregation is induced and controlled only by the suspension pH conditions. It is found that the 100 nm spherical aggregates can significantly improve the green emissions of the LaPO₄:Ce³⁺,Tb³⁺ nano particles. The intensity of the aggregates can be about 10 times as that of the 80 nm-sized individual ones. This study may provide a useful yet convenient strategy in the improvement and application of nano phosphors.     

The luminescent enhancement of LaPO<Subscript>4</Subscript>:Ce<Superscript>3+</Superscript>,Tb<Superscript>3+</Superscript> nano phosphors by radial aggregation

The rare earth nano phosphors can meet the challenging demand for new functional devices but their luminescence is always poor. Here we report on a simple method to prepare uniform LaPO₄:Ce³⁺,Tb³⁺ sphere-like nano aggregates from the precipitated nano phosphor crystallites without using any additive. The spontaneous aggregation is induced and controlled only by the suspension pH conditions. It is found that the 100 nm spherical aggregates can significantly improve the green emissions of the LaPO₄:Ce³⁺,Tb³⁺ nano particles. The intensity of the aggregates can be about 10 times as that of the 80 nm-sized individual ones. This study may provide a useful yet convenient strategy in the improvement and application of nano phosphors.     

Near-ultraviolet excitable Ca4Y6(SiO4)6O: Ce,Tb white phosphors for light-emitting diodes

The present investigation aims to demonstrate the potentiality of Tb³⁺ and Ce³⁺ co-doped Ca₄Y₆(SiO₄)₆O phosphors. By incorporation of Ce³⁺ into Ca₄Y₆(SiO₄)₆O: Tb³⁺, the excitation band was extended from short-ultraviolet to near-ultraviolet region. The energy transfer from Ce³⁺ to Tb³⁺ in Ca₄Y₆(SiO₄)₆O host was investigated and demonstrated to be a resonant type via a dipole–dipole mechanism with the critical distance of 10.2 Å. When excited by 352 nm, Ca₄Y₆(SiO₄)₆O: Ce³⁺, Tb³⁺ exhibited a brighter and broader violet-blue emission (421 nm) from the Ce³⁺ and an intense green emission (542 nm) from the Tb³⁺. Combining the two emissions whose intensities were adjusted by changing the doping levels of the co-activator, an optimized white light with chromaticity coordinates of (0.278, 0.353) is generated in Ca₄Y₆(SiO₄)₆O: 2% Ce³⁺, 8% Tb³⁺, and this phosphor could be potentially used in near-ultraviolet light-emitting diodes.     

Energy transfer processes in Ce and Tb co-doped Ln2Si2O7 (Ln = Y, Gd)

The Ce³⁺ and Tb³⁺ co-doped Ln₂Si₂O₇ (Ln = Y, Gd) samples were prepared by sol-gel method. Structure characterization of the phosphor was carried out by X-ray diffraction. The luminescence properties of samples were analyzed by measuring the excitation and emission spectra. It was observed that excitation energy can transfer mutually between Ce³⁺ and Tb³⁺ in GPS: Ce³⁺, Tb³⁺ samples, while in Y₂Si₂O₇ :Ce³⁺, Tb³⁺ samples the energy transfer only progresses from Ce³⁺ to Tb³⁺. Based on the energy level diagrams of respective Ce³⁺, Tb³⁺ and Gd³⁺ ion, the detailed pathways for energy transfer are explained.     

Luminescent characteristics of LiSrBO3:M (M = Eu, Sm, Tb, Ce, Dy) phosphor for white light-emitting diode

LiSrBO₃:M (M = Eu³⁺, Sm³⁺, Tb³⁺, Ce³⁺, Dy³⁺) phosphors which have been developed for white light-emitting diodes (LEDs) were synthesized by a normal solid-state reaction. The emission and excitation spectra indicate that these phosphors can be effectively excited by near-ultraviolet light-emitting diodes (UVLED), and exhibit satisfactory red, green and blue performances, respectively, nicely fitting in with the widely applied UV chip. Under the condition of doping charge compensation Li⁺, Na⁺ and K⁺, the luminescence intensities of these phosphors were increased.     

Synthesis and luminescent properties of Tb3+ activated AWO4 based (A = Ca and Sr) efficient green emitting phosphors

Optically efficient terbium activated alkaline earth metal tungstate nano phosphors (AWO₄ [A = Ca, Sr]) with different doping concentrations have been prepared by mechanochemically assisted solid state metathesis reaction at room temperature for the first time. The prepared phosphors were characterized by the X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), Fourier transform Raman (FT-Raman) spectroscopy, photoluminescence and diffuse reflectance spectroscopy measurements. The XRD and Raman spectra results showed that the prepared powders present a scheelite-type tetragonal structure. FTIR spectra exhibited a high absorption band situated at around 850 cm^?1, which was ascribed to the W–O antisymmetric stretching vibrations into the [WO₄]^2? tetrahedron groups and the SEM images reveal that the particle sizes were in the range of 20–60 nm. The excitation and the emission spectra were measured to characterize the luminescent properties of the phosphors. The excitation spectrum exhibits a charge transfer broad band along with some sharp peaks from the typical 4f–4f transitions of Tb³⁺. Under excitation of UV light, these AWO₄:xTb³⁺ (A = Ca, Sr) phosphors showed a strong emission band centered at 545 nm (green) which corresponds to ⁵ D ₄ → ⁷ F ₅ transition of Tb³⁺. Analysis of the emission spectra with different Tb³⁺ concentrations revealed that the optimum dopant concentration for CaWO₄:xTb³⁺ and SrWO₄:xTb³⁺ phosphors are about 8 and 6 mol% of Tb³⁺. The green emission intensity of the solid state meta-thesis prepared CaWO₄:0.08Tb³⁺ and SrWO₄:0.06Tb³⁺ phosphors are 1.5 and 1.2 times greater than that of the commercial LaPO₄:Ce, Tb green phosphor. All properties show that AWO₄:Tb³⁺ (A = Ca, Sr) is a very appropriate green-emitting phosphor for fluorescent lamp applications.     

Photoluminescence properties of Y2O3:Tb and YBO3:Tb green phosphors synthesized by hydrothermal method

In this work, two Tb³⁺ activated green phosphors: Y₂O₃:Tb³⁺ and YBO₃:Tb³⁺ were prepared by hydrothermal method. Photoluminescence properties of both phosphors were studied in details. Both phosphors exhibit similar luminescent characteristics symbolized by the dominant green emission at 545 nm. Concentration quenching occurs at the Tb³⁺ concentration of 1.60 atomic% and 2.57 atomic% for Y₂O₃:Tb³⁺ and YBO₃:Tb³⁺, respectively. Luminescence decay properties were characterized to better understand the mechanism of concentration quenching. Based on the calculation, the concentration quenching in both phosphors was caused by the dipole–dipole interaction between Tb³⁺ ions.     

Ca2SiO4:Ln (Ln = Ce3+, Eu2+, Sm3+) tricolor emission phosphors and their application for near-UV white light-emitting diode

Tricolor emission Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors were synthesized by the conventional solid-state reaction method, and their photoluminescence properties were investigated. Ce³⁺-, Eu²⁺-, or Sm³⁺-doped Ca₂SiO₄ phosphors showed typical blue, green, or red luminescence in the CIE1931 chromaticity diagram, respectively. In addition, the luminescence efficiency of the tricolor emission Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors was evaluated. A series of white light-emitting diode (LED) prototypes were fabricated by combining near-UV LED chip and the as-prepared tricolor emission phosphors with various ratios in weight. White LED prototypes with tunable correlated color temperature and color-rendering index values were realized by controlling the amount of phosphors. The presented results indicated the potential application of Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors in near-UV white LED.     

Photoluminescence of Tb/Ce co-doped aluminum oxynitride powders

Aluminum oxynitride(AlON) phosphors co-doped by Tb³⁺ and Ce³⁺ were synthesized by nitridation of the precursor which was co-precipitated from Al(NO₃)₃ solution and nanosized carbon black at 1750 °C for 2 "hrs" in flowing nitrogen atmosphere. The obtained AlON based powders were composed of polycrystalline spinel typed particles with sizes in the range of 1-3 μm. Under an excitation of 275 nm, it was found that co-doping of Ce³⁺ could drastically enhance the luminescence of AlON:Tb³⁺ powder by energy transfer. The product with 0.5 mol% Ce³⁺ and 0.67 mol% Tb³⁺ exhibited a strong broad green emission at 540 nm. The critical quenching concentration of Tb³⁺ in AlON:0.5 mol% Ce³⁺/xmol% Tb³⁺ phosphor was determined to be 0.67 mol%. It was supposed that the mechanism of concentration quenching of Tb³⁺ in AlON:0.5 mol% Ce³⁺ xmol% Tb³⁺ phosphor was dipole-dipole interaction.     

Hydrothermal synthesis and photoluminescence of SrWO4:Tb novel green phosphor

Tb³⁺-doped SrWO₄ phosphors with a scheelite structure have been prepared by hydrothermal reaction. X-ray powder diffraction, field-emission scanning electron microscopy, photoluminescence excitation and emission spectra and decay curve were used to characterize the resulting samples. Scanning electron microscopy image showed that the obtained SrWO₄:Tb³⁺ phosphors appeared to be nearly spherical and their sizes ranged from 1 to 3 μm. Photoluminescence spectra indicated the phosphors emitted strong green light centered at 545 nm under ultraviolet light excitation. Because 12 at.% SWO₄:Tb³⁺ phosphor exhibits intensive green emission under 254 nm excitation in comparison with the commercial green fluorescent lamp phosphor (LaPO₄:Ce,Tb), the excellent luminescence properties make it a new promising green phosphor for fluorescent lamps application.     

White light generation in Al2O3:Ce:Tb:Mn films deposited by ultrasonic spray pyrolysis

Aluminium oxide (Al₂O₃) films doped with CeCl₃, TbCl₃ and MnCl₂ were deposited at 300 °C with the ultrasonic spray pyrolysis technique. The films were analysed using the X-ray diffraction technique and they exhibited a very broad band without any indication of crystallinity, typical of amorphous materials. Sensitization of Tb³⁺ and Mn²⁺ ions by Ce³⁺ ions gives rise to blue, green and red simultaneous emission when the film activated by such ions is excited with UV radiation. The overall efficiency of such energy transfer results to be about 85% upon excitation at 312 nm. Energy transfer from Ce³⁺ to Tb³⁺ ions through an electric dipole-quadrupole interaction mechanism appears to be more probable than the electric dipole-dipole one. A strong white light emission for the Al₂O₃:Ce³⁺(1.3 at.%):Tb³⁺(0.2 at.%):Mn²⁺(0.3 at.%) film under UV excitation is observed. The high efficiency of energy transfer from Ce³⁺ to Tb³⁺ and Mn²⁺ ions, resulting in cold white light emission (x = 0.30 and y = 0.32 chromaticity coordinates) makes the Ce³⁺, Tb³⁺ and Mn²⁺ triply doped Al₂O₃ film an interesting material for the design of efficient UV pumped phosphors for white light generation.     

Strong luminescence and efficient energy transfer in Eu3+/Tb3+-codoped ZnO nanocrystals

Single crystalline Eu³⁺/Tb³⁺-codoped ZnO nanocrystals have been synthesized by using a simple co-precipitation method. Successful doping is realized so that strong green and red luminescence can be efficiently excited by ultraviolet and near ultraviolet radiation, demonstrating an efficient energy transfer from ZnO host to rare earth ions. The energy transfer from the ZnO host to Tb³⁺ in ZnO: Tb³⁺ samples and ZnO host to Eu³⁺ in the ZnO: Eu³⁺ samples under UV excitation are investigated. It is found that the red ⁵D₀ → ⁷F₂ emission of Eu³⁺ ions decreases with increasing temperature but the green ⁵D₄ → ⁷F₅ emission of Tb³⁺ ions increases with increasing temperature, implying a different energy transfer processes in the two samples. Moreover, energy transfer from Tb³⁺ ions to Eu³⁺ ions in ZnO nanocrystals is also observed by analyzing luminescence spectra and the decay curves. By adjusting the doping concentration, the Eu³⁺/Tb³⁺-codoped ZnO phosphors emit green and red luminescence with chromaticity coordinates near white light region, high color purity and high intensity, indicating that they are promising light-conversion materials and have potential in field emission display devices and liquid crystal display backlights.     

The effect of AlN and flux addition on luminescence properties of Ce doped TAG phosphor for white light emitting diodes

A series of Ce³⁺-activated Tb₃Al₅O₁₂ green-yellow phosphors were synthesized using solid state reaction method. The X-ray diffraction peaks of the synthesized phosphor were well matched to the Tb₃Al₅O₁₂ reference peak data. As the addition amount of AlN increase, the relative intensity of diffraction peak increase. But, the addition amount of AlN is over 0.3 mol, the second phase TbAlO₃ diffraction peaks increase. When the addition amount of AlN is 0.3 mol, PL shows the highest emission efficiency. These results were explained by the reducing atmosphere made using AlN. The highest emission intensity was observed when the Ce³⁺ concentration is 0.25 mol. The emission intensity of the Tb_2.75Al₅O₁₂:Ce_0.25³⁺ phosphors were increased by adding BaF₂ and KNO₃ as a flux. The yellow emitting Tb₃Al₅O₁₂:Ce³⁺ phosphors obtained could be applied as white LEDs.     

The VUV–vis spectroscopic properties of phosphors Ca3Gd2(1−x)Ln2x(BO3)4 (Ln3+ = Ce,Sm, Eu,Tb)

The spectroscopic properties in VUV–vis range for phosphors calcium and gadolinium double borate Ca₃Gd₂(BO₃)₄ doped with rare-earth ions Ce³⁺, Sm³⁺, Eu³⁺ and Tb³⁺ were investigated. The host-related absorption, the f–d transitions of Ce³⁺ and Tb³⁺, as well as the charge transfer transitions of Sm³⁺ and Eu³⁺ in the host lattice are assigned and discussed. The CIE chromaticity coordinates for Eu³⁺- and Tb³⁺-activated phosphors are calculated.     

Strong blue, green and red light emission at elevated temperatures from Y2SiO5 doped by the rare-earth ions

The temperature dependence of the photoluminescence (PL) of the rare-earth ion activated Y₂SiO₅ was investigated from room temperature to 573 K. Ion activators such as Eu³⁺, Ce³⁺, Sm³⁺, Tb³⁺ and some of their combinations were studied in this study. The most efficient blue, green and red phosphors at elevated temperature were found by doping the (Ce³⁺ + Tb³⁺), Tb³⁺ and Eu³⁺ respectively, in this material system. Meanwhile, the relationship between the structure and the temperature dependence of the PL in Re _x Y_2–x SiO₅ was also discussed.