Novel Dy-doped Ca2Gd8(SiO4)6O2 white light phosphors for Hg-free lamps application

The luminescent properties of Ca₂Gd_8(1−x)(SiO₄)₆O₂:xDy³⁺ (1% ≤ x ≤ 5%) powder crystals with oxyapatite structure were investigated under vacuum ultraviolet excitation. In the excitation spectrum, the peaks at 166 nm and 191 nm of the vacuum ultraviolet region can be assigned to the O²⁻ → Gd³⁺, and O²⁻ → Dy³⁺ charge transfer band respectively, which is consistent with the theoretical calculated value using Jφrgensen's empirical formula. While the peaks at 183 nm and 289 nm are attributed to the f-d spin-allowed transitions and the f-d spin-forbidden transitions of Dy³⁺ in the host lattice with Dorenbos's expression. According to the emission spectra, all the samples exhibited excellent white emission under 172 nm excitation and the best calculated chromaticity coordinate was 0.335, 0.338, which indicates that the Ca₂Gd₈(SiO₄)₆O₂:Dy³⁺ phosphor could be considered as a potential candidate for Hg-free lamps application.     

Photoluminescence of Eu activated YAlO3 under UV-VUV excitation

YAlO₃ and YAlO₃:Eu³⁺ powder phosphors were prepared by the citric-gel method, and the formation of purified crystalline phases of YAlO₃ and YAlO₃:Eu³⁺ was dependent on the pH value of the starting solution. The powders prepared with pH 3 yielded a single phase YAlO₃ after calcinations at 1000 °C. The spectroscopic properties in UV-vacuum ultraviolet (VUV) range for the orthorhombic structure phosphors YAlO₃:Eu³⁺ were investigated. The broad band centered at 240 nm was assigned to the charge transfer transition between Eu³⁺ and the neighboring oxygen anions. The other broad band from 120 nm to 160 nm was attributed to the host absorption, which ensures the efficient absorption of the Xe plasma emission lines. The photoluminescent spectra showed the strongest emission at 614 nm corresponding to the electric dipole ⁵D₀ → ⁷F₂ transition of Eu³⁺, which resulted in good color purity for display and lamps applications.     

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).     

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.     

A novel red long lasting phosphorescent (LLP) material β-Zn3(PO4)2:Mn, Sm

A novel red long lasting phosphorescent materials β-Zn₃(PO₄)₂:Mn²⁺,Sm³⁺ is firstly synthesized by high-temperature solid-state reaction. The influence of Sm³⁺ ions on luminescence and long lasting phosphorescence properties of Mn²⁺ in phosphor β-Zn₃(PO₄)₂:Mn²⁺,Sm³⁺ are systematically investigated. It is found that the red phosphorescence (λ = 616 nm) performance of Mn²⁺ ion such as brightness and duration is largely improved when Sm³⁺ ion is co-doped into the matrix in which Mn²⁺ ion acts as luminescent center and Sm³⁺ ion plays an important role of electron trap. Thermoluminescence spectrums show that there exists one peak in β-Zn₃(PO₄)₂:Mn²⁺,Sm³⁺, the depth of which is 0.33 eV, and that there are three peaks in β-Zn₃(PO₄)₂:Mn²⁺, among which the depth of the lowest temperature peak in β-Zn₃(PO₄)₂:Mn²⁺ is 0.37 eV. Such differences in the trap depth result in the improvement of red long lasting phosphorescence of Mn²⁺ in present matrix.     

Vacuum ultraviolet excited photoluminescence properties of novel Na3Y9O3(BO3)8:Eu phosphor

The novel vacuum ultraviolet (VUV) excited Na₃Y₉O₃(BO₃)₈:Eu³⁺ red phosphor was synthesized and the photoluminescence (PL) properties were investigated. The phosphor showed strong VUV PL intensity, large quenching concentration (40 mol%) and good chromaticity (0.649, 0.351). The Eu³⁺-O²⁻ charge transition (CT) was observed to be at a higher energy (232 nm, 5.35 eV). The host absorption at 127-166 nm was broad and strong when monitoring the Eu³⁺ emission, which indicated that energy transfer from the host-lattice to the Eu³⁺ ions was efficient in Na₃Y₉O₃(BO₃)₈:Eu³⁺. These excellent VUV PL properties were revealed to be correlated with the unique isolated layer-type structure of Na₃Y₉O₃(BO₃)₈ host. The results showed that the Na₃Y₉O₃(BO₃)₈:Eu³⁺ would be a good candidate for VUV-excited red phosphor.     

Luminescent properties of Sr2P2O7:Eu,Mn phosphor under near UV excitation

The phosphors in the system Sr_2−x−yP₂O₇:xEu²⁺,yMn²⁺ were synthesized by solid-state reactions and their photoluminescence properties were investigated. These phosphors have strong absorption in the near UV region, which is suitable for excitation of ultraviolet light emitting diodes (UVLEDs). The orange-reddish emission of Mn²⁺ in these phosphors can be used as a red component in the tri-color system and may be enhanced by adjusting the Mn²⁺/Eu²⁺ ratio. The energy transfer from Eu²⁺ to Mn²⁺ is observed with a transfer efficiency of ∼0.45 and a critical distance of ∼10 Å. The results reveal that Sr_2−x−yP₂O₇:xEu²⁺,yMn²⁺ phosphors could be used in white light UVLEDs.     

A potential Eu-activated Ca10K(PO4)7 red phosphor for white light-emitting diodes

New red Ca₁₀K(PO₄)₇:Eu³⁺, K⁺ phosphors were synthesized by solid state reaction and their photoluminescence properties as well as those by co-doping Mo⁶⁺ under near ultraviolet excitation were investigated. From the excitation spectra monitored at 611 nm, it can be seen that the strongest excitation peak is situated at 393 nm, well matching with the emission wavelength of near-ultraviolet chips for white LEDs. Upon 393 nm excitation, the brightness of Ca₉K(PO₄)₇:0.5Eu³⁺, 0.5 K⁺ with the optimal Eu³⁺-doping concentration is about 2.3 times stronger than that of the commercial red Y₂O₃:Eu³⁺ phosphor. The introducing of Mo⁶⁺, which results in a possible variety for the excited energy level of the host, can enhance the brightness of Eu³⁺ to be maximized by about 15%. The CIE chromaticity coordinates of Ca₉K(PO₄)₇:0.5Eu³⁺, 0.5 K⁺ are calculated to (0.654, 0.345), which are close to the (0.67, 0.33) standard of the National Television System Committee. All the above results indicate Eu³⁺-activated Ca₁₀K(PO₄)₇ is a potential candidate for white LEDs.     

Growth and optical properties of Er,Yb:YAl3(BO3)4 crystal

Single crystal of erbium, ytterbium-codoped yttrium aluminum tetraborate Er,Yb:YAl₃(BO₃)₄(Er,Yb:YAB) has been grown by the flux method. The absorption spectrum in the visible and NIR regions of Er,Yb:YAl₃(BO₃)₄ crystal are measured at room temperature and fluorescence spectrum of Er,Yb:YAl₃(BO₃)₄ crystal are also measured at room temperature, excited by 976 nm laser. Not only the strong NIR emission peaks located at 1548 nm was observed, but also the visible up-conversion luminescence has been found. The specific heat of the Er/Yb:YAB crystal at room temperature is 0.81 J/g °C.     

Novel red phosphors Na2CaSiO4:Eu for light-emitting diodes

Novel red phosphors Na₂CaSiO₄:xEu³⁺ were synthesized using high temperature solid-state reaction and their luminescence characteristics were investigated for the first time. The excitation spectra indicate that the Na₂CaSiO₄:xEu³⁺ phosphors can be effectively excited by ultraviolet (393 nm) light. The emission spectra of Na₂CaSiO₄:xEu³⁺ phosphors invariably exhibit four peaks assigned to the ⁵D₀-⁷F_J (J = 1, 2, 3 and 4) transitions of Eu³⁺ under 393 nm excitation. The Commission Internationale de l’Eclairage (CIE) chromaticity coordinates and quantum efficiency (QE) are (0.66, 0.34) and 58.9%, respectively. The good color saturation and high quantum efficiency indicate that Na₂CaSiO₄:Eu³⁺ phosphors are potential candidate for light-emitting diodes.     

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.     

Enhanced luminescence by charge compensation in red-emitting Eu-activated Ca3Sr3(VO4)4

The effects of charge compensation on the luminescence behavior of a red-emitting phosphor, Ca₃Sr₃(VO₄)₄:Eu³⁺, were investigated. It has been observed that charge compensated by monovalent ions, especially Na⁺, shows greatly enhanced red emission under ultraviolet excitation. It is found that Na₂CO₃ addition acts as a fluxing agent and plays a role in charge compensation, which clearly improves the emission intensity of Eu³⁺-activated Ca₃Sr₃(VO₄)₄. Enhanced emission intensity of the corresponding charge compensated phosphors under ultraviolet radiation may find application in the production of red phosphors for white light-emitting diodes.     

Photoluminescence and low-voltage cathodoluminescence characteristics of blue phosphor, ZnGa2O4:M (M = Na, Ag)

Photoluminescence and low-voltage cathodoluminescence characteristics of ZnGa₂O₄ phosphor doped with monovalent ions has been studied. Monovalent ions such as Na⁺ and Ag⁺ are incorporated into ZnGa₂O₄ lattices in order to increase the concentration of oxygen vacancies in the spinel lattice. By doping low concentrations of monovalent ions (Na⁺, Ag⁺) into ZnGa₂O₄, the self-activated blue luminescence originated from oxygen vacancies is enhanced. Also, the blue luminescence intensity is enhanced more along with a good color purity by annealing ZnGa₂O₄:Na⁺ in a reducing atmosphere, which is due to increasing the concentration of oxygen vacancies even more. The luminescence band at the UV region (λ_max=360 nm) does not become the major luminescence band by introducing Na⁺ ion into the ZnGa₂O₄ lattice, while the UV luminescence band becomes the major one by annealing the undoped ZnGa₂O₄ in a reducing atmosphere.     

Preparation, structure and luminescent properties of a new potassium yttrium borate K3Y3(BO3)4

A new yttrium borate compound K₃Y₃(BO₃)₄ has been obtained in the K₂O-Y₂O₃-B₂O₃ ternary system. Its structure, determined from single crystal X-ray diffraction data, shows that it belongs to space group P2₁/c with unit cell dimensions of a = 10.4667(16) Å, b = 17.361(3) Å, c = 13.781(2) Å and β = 110.548(8)°. The structure consists sheets of [Y₈B₈O₂₄]_∞ linked by out of sheet BO₃ groups and Y ions to form a three-dimensional framework. The luminescent properties of Eu³⁺ and Tb³⁺ doped K₃Y₃(BO₃)₄ materials have also been studied.     

Synthesis and photoluminescence of nano-Y2O3:Eu phosphors

We report nano-Y₂O₃:Eu³⁺ phosphors with particle size of about 50 nm and relatively high photoluminescence (PL) intensity which is close to the standard for application. The influences of the dope amount, the surfactant and the precipitation pH on the PL intensity, the particle size and the dispersion have been studied. It has been found that 4% is the best Eu³⁺ molar concentration to get the highest PL intensity for both nano- and micro-Y₂O₃:Eu³⁺. The addition of butanol as a surfactant inhibits the grain growth and the agglomeration of particles efficiently by reducing the oxygen bridge bonds. As the pH rises, the PL intensity and the particle size increase due to the formation of oxygen bridge bonds.     

Synthesis and optical properties of (Gd1−x,Eux)2O2SO4 nano-phosphors by a novel co-precipitation method

(Gd_1−x,Eu_x)₂O₂SO₄ nano-phosphors were synthesized by a novel co-precipitation method from commercially available Gd₂O₃, Eu₂O₃, H₂SO₄ and NaOH starting materials. Composition of the precursor is greatly influenced by the molar ratio of NaOH to (Gd_1−x,Eu_x)₂(SO₄)₃ (the m value), and the optimal m value was found to be 4. Fourier transform infrared spectrum (FT-IR) and thermal analysis show that the precursor (m = 4) can be transformed into pure (Gd_1−x,Eu_x)₂O₂SO₄ nano-phosphor by calcining at 900 °C for 2 h in air. Transmission electron microscope (TEM) observation shows that the Gd₂O₂SO₄ phosphor particles (m = 4) are quasi-spherical in shape and well dispersed, with a mean particle size of about 30-50 nm. Photoluminescence (PL) spectroscopy reveals that the strongest emission peak is located at 617 nm under 271 nm light excitation, which corresponds to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The quenching concentration of Eu³⁺ ions is 10 mol% and the concentration quenching mechanism is exchange interaction among the Eu³⁺ ions. Decay study reveals that the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions has a single exponential decay behavior.     

Luminescence characterization of (Ca1−xZnx)Ga2S4:Eu phosphors for a white light-emitting diode

We investigated the luminescence properties of (Ca_1−xZn_x)Ga₂S₄:Eu²⁺ phosphor as a function of Zn²⁺ and Eu²⁺ concentrations. The luminescence intensity was markedly enhanced by increasing the mole fraction of Zn²⁺ at Ca²⁺ sites. Lacking any Zn²⁺ ions, CaGa₂S₄:0.01Eu²⁺ converted only 18.1% of the absorbed blue light into luminescence. As the Zn²⁺ concentration increased, the quantum yield increased and reached a maximum of 24.4% at x = 0.1. Furthermore, to fabricate the device, the optimized green-yellow (Ca_0.9Zn_0.1)Ga₂S₄:Eu²⁺ phosphor was coated with MgO. White light was generated by combining the MgO-coated phosphor and the blue emission from a GaN chip.     

Luminescent properties of Na3YSi3O9 doped with Eu under UV-VUV excitation

The luminescent properties of Na₃Y_1−xSi₃O₉:xEu³⁺ (0.05 ≦ x ≦ 0.80) powder crystals were investigated in UV-VUV region. The Eu³⁺-O²⁻ charge transfer band (CTB) was observed to be located at around 233 nm and the environmental parameter (h_e) was estimated to be about 0.730. The excitation spectrum monitoring the 613 nm red emission from Eu³⁺ ions reveals the host absorption band (HAB) to be around 145 nm. The calculated Commission Internationale de l’Eclairage (CIE) chromaticity coordinates indicate the emission by 233 nm rather than by 147 nm excitation has the better color purity and the possible mechanisms have been proposed. The Eu³⁺-emission showed high quenching concentration due to the isolated YO₆ octahedra in the host and the small h_e for the Eu³⁺ ions and the optimum concentration was determined to be as high as x = 0.65 and 0.30 with 233 and 147 nm excitation, respectively.     

Crystal structure and spectroscopic studies of NaGd(PO3)4

Single crystals of gadolinium–sodium polyphosphate NaGd(PO₃)₄ were grown for the first time using a flux method and characterized by X-ray diffraction. This phosphate crystallizes in a monoclinic system with P2₁/n space group and with the following unit-cell dimensions: a = 9.767(3) Å, b = 13.017(1) Å, c = 7.160(2) Å, β = 90.564(5)°, V = 910.3(4) Å³ and Z = 4. The crystal structure was solved from 3451 X-ray independent reflections with final R(F²) = 0.0219 and R_w(F²) = 0.056 refined with 164 parameters (). The atomic arrangement can be described as a long chain polyphosphate organization. Two infinite (PO₃)∝ chains with a period of eight tetrahedra run along the [0 1 1] direction. The structure of NaGd(PO₃)₄ consists of GdO₈ polyhedra sharing oxygen atoms with phosphoric group PO₄. Each Na⁺ ion is bonded to eight oxygen atoms.     

Synthesis and upconversion luminescence properties of Yb/Er codoped BaGd2(MoO4)4 powder

Synthesis and upconversion luminescence properties of the new BaGd₂(MoO₄)₄:Yb³⁺,Er³⁺ phosphor were reported in this paper. The phosphor powder was obtained by the traditional high temperature solid-state method, and its phase structure was characterized by the XRD pattern. Based on the upconversion luminescence properties studies, it is found that, under 980 nm semiconductor laser excitation, BaGd₂(MoO₄)₄:Yb³⁺,Er³⁺ phosphor exhibits intense green upconversion luminescence, which is ascribed to ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transition of Er³⁺. While the observed much weaker red emission is due to the non-radiative relaxation process of ⁴S_3/2 → ⁴F_9/2 and ⁴F_9/2 → ⁴I_15/2 transition originating from the same Er³⁺. The concentration quenching effects for both Yb³⁺ and Er³⁺ were found, and the optimum doping concentrations of 0.5 mol% Yb³⁺ and 0.08 mol% Er³⁺ in the new BaGd₂(MoO₄)₄ Gd³⁺ host were established.