Investigation of Na3GdP2O8:Tb as a potential green-emitting phosphor for plasma display panels

The photoluminescent properties of a series of Tb³⁺-doped Na₃GdP₂O₈ phosphors excitable by vacuum ultraviolet and ultraviolet light are reported. The host related absorption, f-f and f-d transitions of Gd³⁺ and Tb³⁺, and charge transfer of O²⁻ → Gd³⁺ and O²⁻ → Tb³⁺ are assigned. Under 147 nm light excitation, Na₃GdP₂O₈:Tb³⁺ phosphors show efficient green emissions with a dominant peak at 545 nm. The optimal sample Na₃Gd_0.4Tb_0.6P₂O₈ shows a shorter decay time and a comparable brightness when compared with the commercial Zn₂SiO₄:Mn²⁺ green phosphor. These results demonstrate that it is a potential candidate for plasma display panels application.     

Luminescence excitation spectra of TbX3 (X = Cl, Br, I)

A systematic study of the excitation spectrum of TbX₃ (X = Cl⁻, Br⁻, I⁻) is presented in this work. In general, the excitation spectra of TbX₃ can be divided into three major regions: (1) the short-wave host lattice absorption region, (2) the intermediate absorption region where the Tb³⁺ 4f⁸ → 4f⁷5d¹ interconfigurational excitation transition are located, and (3) the long-wave excitation region where the Tb³⁺ 4f⁸ → 4f⁸ intraconfigurational excitation transition are located. The high spin and the low spin components of the Tb³⁺ interconfigurational excitation transition are clearly identified in the case of TbCl₃. The luminescence of TbX₃ (X = Cl⁻, Br⁻, I⁻) is dominated by emission transitions emanating from the Tb³⁺⁵D₄ state. A comparative study of the optical properties of TbX₃ (X = Cl⁻, Br⁻, I⁻) with the properties of the Tb³⁺ ion in several halide host lattices is presented. Further, a comparative study of the fundamental host lattice optical transitions in terbium halides and other halide materials is also presented.     

Optical characterization of Bi doped SrS nanophosphors

Optical properties of Bi³⁺ doped SrS nanophosphors synthesized by solid state diffusion method in the presence of sodium thiosulfate as a flux have been reported. UV-vis absorption and photoluminescence (PL) spectra of SrS phosphors doped with trivalent Bi³⁺ ions either alone or in combination with charge compensating ions, were also studied. These studies reflect that the incorporation of Bi³⁺ into host lattice is facilitated by the charge compensating Na⁺ ions. PL emission for SrS:Bi shows a peak at 481 nm at an excitation wavelength of 430 nm, which is attributed to the transition from the ³P₁ to ¹S₀ states of Bi³⁺. We have also investigated the effect of different dopant concentrations on PL emission intensity.     

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.     

Luminescence properties of LaPO4:Tb,Me (Me = Gd, Bi, Ce) under VUV excitation

The luminescence properties of LaPO₄:Tb³⁺,Me³⁺ (Me = Gd, Bi, Ce) were investigated under VUV excitation. The results indicate that only Gd³⁺ plays an intermediate role in energy transfer from the host absorption band to Tb³⁺ under 147 nm excitation, Bi³⁺ and Ce³⁺ have no contribution to improving the emission intensity of La_0.95PO₄:Tb_0.05³⁺ because the charge transfer band of Bi³⁺ is mismatching for the excitation wavelength (147 nm) and Ce³⁺ can be oxidized easily. A new band at 135 nm is observed in the excitation spectrum of La_0.92PO₄:Tb_0.05³⁺,Bi_0.03³⁺, which may correlate with the absorption of Bi²⁺.     

The photoluminescence properties of Eu,Bi co-doped yttrium oxysulfide phosphor under vacuum ultraviolet excitation

Y₂O₂S co-doped with Bi³⁺,Eu³⁺ phosphors were prepared and their luminescence properties under vacuum ultraviolet (VUV) excitation were investigated. Much stronger red emission for Y₂O₂S:Eu³⁺,Bi³⁺ were observed under 147 nm excitation than that for Y₂O₂S:Eu³⁺. Investigation on photoluminescence and calculation of electronic structure of Y₂O₂S:Eu³⁺,Bi³⁺ revealed that the Bi³⁺ acts as a medium in energy transfer process and the great VUV luminescence enhancement of Y₂O₂S:Eu³⁺ by doping Bi³⁺ is due to effective energy transfer process: charge transfer (CT) transition of Y³⁺-O²⁻ → Bi³⁺ → Eu³⁺. The Y₂O₂S:Eu³⁺,Bi³⁺ showed excellent optical properties when compared with the commercial (Y,Gd)BO₃:Eu³⁺. Thus, the Y₂O₂S:Eu³⁺,Bi³⁺ would be a promising VUV-excited red phosphor.     

Green-emitting Yb-doped α-SiAlON phosphors prepared by spark plasma sintering

Divalent ytterbium-doped Ca-α-SiAlON phosphors were synthesized by a spark plasma sintering (SPS) method without a reducing gas. A single phase Ca-α-SiAlON:Yb²⁺ was successfully achieved at relatively low temperature of 1600 °C. Its photoluminescence excitation spectrum showed a broad band peaking at 450 nm due to the 4f¹³5d¹ → 4f¹⁴ transition of Yb²⁺ ions, while a corresponding green emission band was observed at 545 nm. The post-annealing in a reduced atmosphere significantly improved the luminescent properties by increasing the crystallinity, reducing the carbon contamination, and changing the residual Yb³⁺ to Yb²⁺ in as-synthesized samples. The post-annealed powders, compared to commercial YAG:Ce³⁺ and silicate phosphors, showed a low thermal quenching due to the rigid crystal structure.     

Hydrothermal synthesis and luminescent properties of Y2O3:Tb and Gd2O3:Tb microrods

One-dimensional (1D) Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺ microrods have been successfully prepared through a large-scale and facile hydrothermal method followed by a subsequent calcination process in N₂/H₂ mixed atmosphere. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR), thermogravimetric analysis (TGA), energy-dispersive X-ray spectra (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL) and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The as-formed products via the hydrothermal process could transform to cubic Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺ with the same morphology and slight shrinking in size after a postannealing process. Both Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺ microrods exhibit strong green emission corresponding to ⁵D₄ → ⁷F₅ transition (542 nm) of Tb³⁺ under UV light excitation (307 and 258 nm, respectively), and low-voltage electron beam excitation (1.5 → 3.5 kV), which have potential applications in fluorescent lamps and field emission displays.     

Photoluminescence of Tb and Mn activated Ca8MgGd(PO4)7 under vacuum ultraviolet excitation

Novel Tb³⁺ and Mn²⁺ activated Ca₈MgGd(PO₄)₇ phosphors were synthesized by solid-state reaction and their photoluminescence properties in vacuum ultraviolet region were investigated for the first time. It can be observed from the excitation spectra that the host-related absorption band is located around 170 nm, and it overlaps the O²⁻ → Tb³⁺ charge transfer band of Ca₈MgGd(PO₄)₇:Tb³⁺ around 161 nm and the 3d⁵ → 3d⁴4s transition band of Ca₈MgGd(PO₄)₇:Mn²⁺ near 200 nm. The 4f-4f 5d spin-allowed and spin-forbidden transitions of Tb³⁺ are verified to be located at 170-250 and 257-271 nm, respectively. Upon 147 nm excitation, the dominant emission peak intensity of the Ca₈MgGd_0.1(PO₄)₇:0.9Tb³⁺ phosphor is about 2.7 times stronger than that of the commercial Zn₂SiO₄:Mn²⁺ green phosphor, and the brightness of the former with a short decay time of 2.5 ms is about 98% of the latter’s. The Ca₈MgGd(PO₄):Mn²⁺ phosphor excited at 147 nm exhibits a deep red emission around 650 nm, which could be attributed to the ⁴T₁ → ⁶A₁ transition of Mn²⁺, with the CIE index (0.679, 0.321). In a word, the results above indicate that both Tb³⁺ and Mn²⁺ activated Ca₈MgGd(PO₄)₇ phosphors could be promising for PDP or Hg-free lamp applications.     

A novel green luminescent material AlPO4:Tb

A novel green phosphor Tb³⁺ doped AlPO₄ was synthesized by conventional solid-state reaction method. The phosphor showed prominent luminescence in green due to the ⁵D₄-⁷F₅ transition of Tb³⁺. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis. The XRD measurements indicated that there are no crystalline phases other than AlPO₄. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 542 nm under UV excitation. It is shown that the 3 mol% of doping concentration of Tb³⁺ ions in AlPO₄:Tb³⁺ phosphor is optimum. The measured chromaticity for the phosphors AlPO₄:Tb³⁺ under UV excitation is (0.32, 0.53).     

Photoluminescence properties of NaGd(MoO4)2:Eu nanophosphors prepared by sol-gel method

NaGd(MoO₄)₂:Eu³⁺ (hereafter NGM:Eu) phosphors have been prepared by sol-gel method. The properties of the resulting phosphors are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and decay curve. The excitation spectra of NGM:Eu phosphors are mainly attributed to O → Mo charge-transfer (CT) band at about 282 nm and some sharp lines of Eu³⁺ f-f transitions in near-UV and visible regions with two strong peaks at 395 and 465 nm, respectively. Under the 395 and 465 nm excitation, intense red emission peaked at 616 nm corresponding to ⁵D₀ → ⁷F₂ transition of Eu³⁺ are observed for 35 at.% NGM:Eu phosphors as the optimal doping concentration. The luminescence properties suggest that NGM:Eu phosphor may be regarded as a potential red phosphor candidate for near-UV and blue light-emitting diodes (LEDs).     

Luminescent properties of a novel green-emitting gallium borate phosphor under vacuum ultraviolet excitation

Vacuum ultraviolet (VUV) excitation and emission properties of a new Tb³⁺-activated green-emitting phosphor with huntite-type gallium borate, LnGa₃(BO₃)₄:Tb³⁺ (Ln = Y, Gd), are investigated. Overall absorption bands are in the range of 120-250 nm and can be tentatively interpreted in terms of the charge transfer transition from host to rare earth ions and the Tb³⁺ activator. Additionally, an appropriate atomic ratio of Y³⁺/Gd³⁺ in the host compound enhances both the excitation and emission efficiency under VUV excitation. Enhanced absorption efficiency for the VUV light makes these novel phosphors the prominent luminescent materials with plasma-discharge conditions, by converting the VUV radiation to the visible light.     

Photoluminescence properties of Eu doped Ba2ZnS3 phosphor for white light emitting diodes

The synthesis and photoluminescence properties of novel Eu²⁺ doped Ba₂ZnS₃ phosphors for white light emitting diodes (LEDs) are reported. Diffuse reflection spectra of Ba₂ZnS₃ host and synthesized phosphors have been measured. The excitation spectra of synthesized phosphors consist of three broad bands between 250 nm and 550 nm and are consistent with the diffuse reflectance spectra. The emission spectra show the characteristic 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ion and there exists efficient energy transfer from host to Eu²⁺ ions when excited by 350-nm light. The dependence of emission spectra on temperature is also measured; the possible reasons applied to explain the experimental results are also discussed. The fluorescence lifetime of Eu²⁺ in Ba_1.995ZnS₃:0.005Eu²⁺ is measured and the values are 1.49 and 23.4 μs.     

Luminescence of SrGdGa3O7:RE(RE = Eu, Tb) phosphors and energy transfer from Gd to RE

Eu³⁺- and Tb³⁺-activated SrGdGa₃O₇ phosphors were synthesized by the solid-state reaction and their luminescence properties were investigated. Sr(Gd_1 − xEu_x)Ga₃O₇ and Sr(Gd_1 − xTb_x)Ga₃O₇ formed continuous solid solution in the range of x = 0-1.0. Unactivated SrGdGa₃O₇ exhibited a typical characteristic excitation and emission of Gd ion. The SrGdGa₃O₇:xEu³⁺ and SrGdGa₃O₇:xTb³⁺ phosphors also showed the well-known Eu³⁺ and Tb³⁺ excitation and emission. The energy transfer from Gd³⁺ to Eu³⁺ and Tb³⁺ were verified by photoluminescence spectra. The dependence of photoluminescence intensity on Eu³⁺ and Tb³⁺ concentration were also studied in detail and the photoluminescence (PL) intensity of SrGdGa₃O₇:Eu and SrGdGa₃O₇:Tb were compared with commercial phosphors, Y₂O₃:Eu and LaPO₄:Ce,Tb. The luminescence decay measurements showed that the lifetimes of Eu³⁺ and Tb³⁺ were in the range of microsecond. The energy transfer from Gd³⁺ to Tb³⁺ was also observed in decay curve.     

Novel blue-emitting phosphor NaMg4(PO4)3:Eu, Ce with energy transfer

A blue-emitting phosphor of NaMg₄(PO₄)₃:Eu²⁺, Ce³⁺ was prepared by a combustion-assisted synthesis method. The phase formation was confirmed by X-ray powder diffraction measurement. Photoluminescence excitation spectrum measurements show that the phosphor can be excited by near UV light from 230 to 400 nm and presents a dominant luminescence band centered at 424 nm due to the 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions at room temperature. Effective energy transfer occurs in Ce³⁺/Eu²⁺ co-doped NaMg₄(PO₄)₃ due to large spectral overlap between the emission of Ce³⁺ and excitation of Eu²⁺. Co-doping of Ce³⁺ enhances the emission intensity of Eu²⁺ greatly by transferring its excitation energy to Eu²⁺, and Ce³⁺ plays a role as a sensitizer. Ce³⁺-Eu²⁺ co-doped NaMg₄(PO₄)₃ powders can possibly be applied as blue phosphors in the fields of lighting and display.     

Synthesis and luminescence properties of color-tunable Ba1−ySryLa4−xTbx(WO4)7 (x = 0.02-1.2, y = 0-0.4) phosphors

Ba_1−ySr_yLa_4−xTb_x(WO₄)₇ (x = 0.02-1.2, y = 0-0.4) phosphors were prepared via a solid-state reaction and their photoluminescence properties were investigated. An analysis of the decay behavior indicates that the energy migration between Tb³⁺ ions is conspicuous in the ⁵D₃ → ⁷F₄ transition due to the cross-relaxation in BaLa₄(WO₄)₇. A partial substitution of Ba²⁺ by Sr²⁺ can not only enhance the emission intensity but also increase the solid solubility of Tb³⁺ in Ba_1−ySr_yLa_4−xTb_x(WO₄)₇. The emission intensity of the ⁵D₄ → ⁷F_J (J = 4, 5, 6) transitions can be enhanced by increasing Sr²⁺ and Tb³⁺ concentrations, with the optimal conditions being x = 1.2, y = 0.4 (Ba_0.6Sr_0.4La_2.8Tb_1.2(WO₄)₇). Under near-UV excitation at 379 nm, the CIE color coordinates of Ba_1−ySr_yLa_4−xTb_x(WO₄)₇ vary from blue (0.212, 0.181) at x = 0.04, y = 0, to green (0.245, 0.607) at x = 1.2, y = 0.4.     

Enhanced luminescence properties of YBO3:Eu phosphors by Li-doping

Different concentrations of Li-doped YBO₃:Eu³⁺ phosphors have been prepared by the conventional solid state reaction method and were characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence excitation and emission measurements. An intense reddish orange emission is observed under UV excitation and the emitted radiation was dominated by an orange peak at 594 nm resulted from the ⁵D₀ → ⁷F₁ transitions of Eu³⁺ ions. The brightness of the YBO₃:Eu³⁺ phosphor was found greatly improved with Li-doping accompanied by slight improvement in the purity of the color which might be attributed to improvement in crystallinity, grain sizes and creation of oxygen vacancies with Li-doping. The observed results have been discussed in comparison with similar reported works.     

M2Y8(SiO4)6O2: Tb (M = Ca, Sr) phosphors: Sol-gel synthesis from N-2-aminoethylic-3-aminopropyldiethoxysilane and different photoluminescence behavior

M₂Y₈(SiO₄)₆O₂: Tb³⁺ (M = Ca, Sr) phosphors have been synthesized with a new silicon source silane crosslinking reagent (N-2-aminoethylic-3-aminopropyldiethoxysilane [NH₂(CH₂)₂NH(CH₂)₃SiCH₃(OCH₃)₂], abbreviated as AEAPMMS) through the sol-gel process, both of which present the characteristic emission ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) of Tb³⁺ ions. It is interesting to be found that the high energy level blue emission (⁵D₃ → ⁷F_J (J = 6, 5, 4, 3) transition) still can be found in the emission spectrum of Ca₂Y₈(SiO₄)₆O₂: Tb³⁺ while it disappears in the emission spectrum of Sr₂Y₈(SiO₄)₆O₂: Tb³⁺ for the cross-relaxation-induced quenching.     

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.     

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.