Ce to Tb energy transfer in alkaline earth (Ba, Sr or Ca) sulphate phosphors

Energy transfer between Ce³⁺ and Tb³⁺ dopants in alkaline earth (Ba, Sr or Ca) sulphate phosphors is investigated. Among these three phosphors, CaSO₄:Ce³⁺,Tb³⁺ showed maximum Tb³⁺ green emission on excitation with UV light. Photoluminescence measurements reveal that the emission intensity from CaSO₄:Ce³⁺,Tb³⁺ is comparable with that of the commercial green lamp phosphor Ce_0.65Tb_0.35MgAl₁₁O₁₉. Optimum concentrations of dopants in CaSO₄:Ce³⁺,Tb³⁺ are 0.2 mol% each and the optimum sintering treatment following re-crystallisation is 600 °C for 1 h duration. The effect of charge compensator in all the three phosphors is also studied.     

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.     

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.     

Luminescence properties and energy transfer investigations of Ce3+/Tb3+ co-doped BaY2Si3O10 phosphor

A novel phosphor BaY₂Si₃O₁₀ (BYSO): Ce³⁺, Tb³⁺ was synthesized by the conventional solid-state reaction, which displays tunable color emission from blue to blue-green under ultraviolet excitation by adjusting the radio of Ce³⁺ and Tb³⁺ appropriately. Photoluminescence characteristics were carefully investigated. We demonstrate the existence of efficient energy transfer from Ce³⁺ to Tb³⁺ in BaY₂Si₃O₁₀: Ce³⁺, Tb³⁺ phosphor. The energy transfer Ce³⁺ → Tb³⁺ was proved to be governed by dipole–quadrupole interaction.     

Luminescence enhancement of Tb3+ in Sr3SiO5:Eu2+ phosphor

Sr₃SiO₅ phosphors co-doped with Eu²⁺ and Tb³⁺ were prepared by a conventional solid-state reaction method. The prepared Sr₃SiO₅:Eu²⁺,Tb³⁺,Li⁺ phosphors had characteristic luminescent spectra excited under near-UV excitation in which both the broadband spectrum assigned to Eu²⁺ and the line spectrum assigned to Tb³⁺ are observed, although Tb³⁺ is inactive with this photon energy in general. For Eu²⁺–Tb³⁺ codoped Sr₃SiO₅, energy transfer process takes place and the mechanism is ascribed to the overlap between the shorter Eu²⁺ luminescence band from the Sr₃SiO₅ crystal structure with two Sr sites and ₅D⁴ energy level of Tb³⁺ ion. Due to the energy transfer, PL intensity of Eu²⁺ emission increased about 26 %. We suggest that this enhancement mechanism could shed light on the potential applications in white light-emitting diodes excited by near-UV light. In addition, the emission peak position near the orange region indicates that our system is a step towards a new class of wavelength sources for artificial lighting with improved PL intensity and lower energy consumption.     

VUV sensitization of Mn2+ emission by Tb3+ in strontium aluminate phosphor

The luminescence properties of green emitting strontium aluminate phosphor SrAl₁₂O₁₉ doped and co-doped with Mn²⁺ and Tb³⁺ were studied using synchrotron radiation. It is shown that Tb³⁺, exhibiting a strong absorption band in the vacuum-ultraviolet (VUV), provides sensitisation of Mn²⁺ emission in this host. The observed sensitisation effect of the Tb–Mn pair can be used for improving the efficiency of VUV phosphors.     

Controllable hydrothermal synthesis and morphology evolution of Zn4B6O13:Tb/Eu phosphors with tunable luminescent properties

A series of Tb, Eu single or co-doped Zn₄B₆O₁₃ phosphors with tetrahedral morphology were synthesized by facile hydrothermal method. The influences of reaction temperature and the pH value of the reaction system on the structures and compositions of product were also investigated, in which four kinds of zinc borates with different structures and compositions (Zn₄B₂O₇·H₂O, Zn₄B₆O₁₃, Zn(H₂O)B₂O₄·0.12H₂O, and H(Zn₆O₂(BO₃)₃)) were obtained. A possible growth mechanism of tetrahedral morphology of Zn₄B₆O₁₃ has been proposed according to reaction time. The obtained samples were characterized by XRD, EDS, SEM, TEM, XPS, BET, DR, PL and QY. XPS results indicate that Eu²⁺ and Tb⁴⁺ are present in Tb/Eu co-doped Zn₄B₆O₁₃, which might be generated from charge transfer between Tb³⁺ and Eu³⁺. The PL results shows that Eu³⁺, Tb³⁺ ion single-doped Zn₄B₆O₁₃ microstructure exhibit orange and green emission under ultraviolet excitation, respectively. Compared to Eu³⁺ and Tb³⁺ single doped Zn₄B₆O₁₃ phosphors, the Eu/Tb co-doped Zn₄B₆O₁₃ phosphors showed stronger blue emission of Eu²⁺. These results imply that the tetrahedral morphology of Eu³⁺, Tb³⁺ ion single-doped and Eu^2+/3+/Tb^3+/4+ co-doped Zn₄B₆O₁₃ phosphors have the promise application for nano/micro-optical functional devices.     

Cold white light generation through the simultaneous emission from Ce3+ and Tb3+ in sodium germanate glass

A spectroscopic investigation of sodium germanate glasses activated with Ce³⁺, Tb³⁺ and Ce³⁺/Tb³⁺ is carried out by analyzing their photoluminescence spectra and decay times. Non-radiative energy transfer from Ce³⁺ to Tb³⁺ is observed upon near-UV excitation at 310 nm (peak emission wavelength of AlGaN-based LEDs). The non-radiative nature of this energy transfer is inferred from the increase in the decay rate of the Ce³⁺ emission when the glass is co-doped with Tb³⁺. From an analysis of the Ce³⁺ emission decay time curve it is inferred that an electric dipole–quadrupole interaction might to be the dominant mechanism for the Tb³⁺ emission sensitized by Ce³⁺. Energy transfer from Ce³⁺ to Tb³⁺ leads to a simultaneous emission of these ions in the blue, green, yellow and red, resulting in white light with CIE1931 chromaticity coordinates, x = 0.30 and y = 0.32, which correspond to cold white light with a colour temperature of 7320 K and very small deviation from the Planckian black-body radiator locus (0.005).     

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.     

Down-shifting in Ce3+–Tb3+ co-doped SiO2–LaF3 nano-glass–ceramics for photon conversion in solar cells

95SiO₂–5LaF₃ sol–gel derived nano-glass–ceramics single doped with Ce³⁺ or Tb³⁺ and co-doped with Ce³⁺–Tb³⁺ were synthesized by thermal treatment of precursor glasses. Precipitation of LaF₃ nanocrystals during ceramming process was confirmed by X-ray diffraction with mean size ranging from 12 to 15 nm. An exhaustive spectroscopic analysis has been carried out. As a result, it was found that the green emission of Tb³⁺ ions was greatly enhanced through down shifting process, due to efficient energy transfer from Ce³⁺ to Tb³⁺ ions in the glass–ceramics, which is favored by the reduction of the interionic distances when the dopant ions are partitioned into LaF₃ nanocrystals. These results suggest the use of these materials to improve the efficiency of solar cells.     

Synthesis of novel halloysite@YF3:Ce3+,Tb3+ nanocomposite for enhanced luminescent properties

A novel halloysite@YF₃: Ce³⁺, Tb³⁺ anocomposite with strong luminescent properties was designed and synthesized by a facile direct precipitation strategy. Owing to the halloysite as a support, it can significantly prevent the aggregation of YF₃:Ce³⁺,Tb³⁺ and the distribution of YF₃:Ce³⁺,Tb³⁺ on halloysite was highly uniform. Importantly, due to the unique surface-interface-dielectric multiple confinement (SIDMC) effects, the as-harvested halloysite@YF₃:Ce³⁺,Tb³⁺ nanocomposite exhibited excellent luminescent performance. Compared with YF₃:Ce³⁺,Tb³⁺, the luminescence intensity of halloysite@YF₃:Ce³⁺,Tb³⁺ nanocomposite is significantly enhanced by about 6 times under 255 nm excitation. However, the fluorescence lifetime of halloysite@YF₃:Ce³⁺,Tb³⁺ nanocomposite (7.21 ms) is shorter than that of YF₃:Ce³⁺,Tb³⁺ nanoparticles (8.34 ms). This finding indicated that halloysite can change the luminescent properties of YF₃:Ce³⁺,Tb³⁺ nanoparticles through an SIDMC effect. The combination of halloysite and YF₃:Ce³⁺,Tb³⁺ nanoparticles not only endowed halloysite with special properties, and effectively tuned the luminescent properties of YF₃:Ce³⁺,Tb³⁺ nanoparticles, thereby improving the utility of halloysite and YF₃:Ce³⁺,Tb³⁺ nanoparticles. The research supplies an insight on the development of natural mineral-based luminescent materials, and hopefully it could promote them application in many fields.     

Color-tunable emission and energy transfer studies in GdOBr:Ce3+ Dy3+ phosphor

Color-tunable blue to bluish white-emitting Ce³⁺/Dy³⁺ co-doped GdOBr phosphors have been synthesized by the conventional solid-state method. The phase structures, luminescent properties and energy transfer process were discussed in detail. Broad-band absorption originating from the f-d transition of Ce³⁺ can be found for the as-prepared GdOBr:Ce³⁺,Dy³⁺ phosphor, and color-tunable blue to bluish white emission can be realized owing to the energy transfer between Ce³⁺ and Dy³⁺. The energy transfer mechanism is demonstrated to be the dipole–dipole process. The energy transfer efficiency increases with increasing Dy³⁺ concentrations. The results indicate that Ce³⁺/Dy³⁺-activated GdOBr phosphors may be potential for phosphor-converted white-light UV-LEDs.     

Spectroscopic characterization and optical waveguide fabrication in Ce, Tb and Ce/Tb doped zinc–sodium–aluminosilicate glasses

A spectroscopy investigation of Ce³⁺ and Tb³⁺ ions in sodium–zinc–aluminosilicate glasses is performed using the photoluminescence technique. Blue–white light, with x = 0.24 and y = 0.24 CIE chromaticity coordinates, is obtained for the Tb³⁺ singly-doped glass excited at 351 nm. When the sodium–zinc–aluminosilicate glass is co-doped with Ce³⁺ and Tb³⁺ a non-radiative energy transfer from Ce³⁺ to Tb³⁺ ions is observed upon 320 nm excitation. From an analysis of the cerium emission decay curve, the Ce³⁺ → Tb³⁺ energy transfer microscopic parameter and efficiency are obtained. Different concentrations of Ce³⁺ and Tb³⁺ ions in the glass host gives rise to blue and blue–green emissions, with different CIE coordinates. Optical waveguides were produced in the samples by Ag⁺–Na⁺ ion-exchange, and their characterization is presented.     

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.     

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.     

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 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.     

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.     

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.     

Enhancement of blue-green photoluminescence in B2O3 fritted ZrO2:Ce3+ phosphor

Blue-green emission of ZrO₂:Ce³⁺ phosphor, prepared by solid-state reaction, is demonstrated. The phosphor presents a strong and broad photoluminescence band centered at 496 nm with excitation at 291 nm. The optimized Ce content is 2.5 mol% for the strongest emission of ZrO₂:Ce³⁺ phosphors prepared without B₂O₃. The PL intensity is enhanced by at least 3 dB by adding 5.0 mol% B₂O₃ within the ZrO₂:Ce³⁺ containing 5.0 mol% Ce during synthesis. Increase of the B₂O₃ flux effectively induces the Ce ions to substitute the Zr ions in ZrO₂ lattice and causes the ZrO₂ lattice distortion. The formation of Ce_0.75Zr_0.25O₂ compound within the ZrO₂:Ce³⁺ occurred when the Ce content is greater than or equal to 2.5 mol% for the phosphors prepared without B₂O₃ and leads to a degradation of the phosphor PL intensity due to the host effect. The addition of B₂O₃ during the preparation of phosphors containing Ce ions lower than or equal to 5.0 mol% essentially restrains the Ce_0.75Zr_0.25O₂ formation and then enhances the blue-green PL.