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.     

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.     

Hydrothermal synthesis and vacuum ultraviolet-excited luminescence properties of novel Dy-doped LaPO4 white light phosphors

Novel LaPO₄:Dy³⁺ white light phosphors with monoclinic system were successfully synthesized by hydrothermal method at 240 °C. The strong absorption at around 147 nm in excitation spectrum was assigned to the host absorption which suggested that the vacuum ultraviolet-excited energy was efficiently transferred from the host to the Dy³⁺ ion. The f-d transition of Dy³⁺ ion was observed locating at 182 nm. Under 147 nm excitation, La_1−xPO₄:xDy³⁺ phosphor exhibited two emission bands locating at 571 nm (yellow) and 478 nm (blue) which corresponded to the hypersensitive transitions ⁴F_9/2-⁶H_13/2 and ⁴F_9/2-⁶H_15/2. It was the two emission bands that lead to the white light.     

Luminescence properties of Ca4Y6(SiO4)6O:RE (RE = Eu, Tb, Dy, Sm and Tm) under vacuum ultraviolet excitation

The vacuum ultraviolet excited luminescent properties of Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺ and Tm³⁺ in the matrices of Ca₄Y₆(SiO₄)₆O were investigated. The bands at about 173 nm in the vacuum ultraviolet excited spectra were attributed to host lattice absorption of the matrix Ca₄Y₆(SiO₄)₆O. For Eu³⁺-doped samples, the O²⁻ → Eu³⁺ CTB was identified at 258 nm. Typical 4f-5d absorption bands in the region of 195-300 nm were observed in Tb³⁺-doped samples. For Dy³⁺-doped and Sm³⁺-doped samples, the broad excitation bands consisted of host absorptions, CTB and f-d transition. For Tm³⁺-doped samples, the O²⁻ → Tm³⁺ CTB was located at 191 nm. About the color purity and emission intensity, Ca₄Y₆(SiO₄)₆O:Tb³⁺ is an attractive candidate of green light PDP phosphor, and Ca₄Y₆(SiO₄)₆O:Dy³⁺ has potential application in the field of mercury-free lamps.     

Photoluminescence investigation of rare-earth activated GdCa3(GaO)3(BO3)4 phosphors under UV excitation

A borate compound was adopted as a new host material of Eu³⁺ and Tb³⁺ activators to fabricate efficient luminescence materials. The phosphor compositions, Gd_1−xEu_xCa₃(GaO)₃(BO₃)₄ and Gd_1−xTb_xCa₃(GaO)₃(BO₃)₄, were synthesized by conventional solid-state reactions. The crystalline phases of the resulting powders were identified using an X-ray diffraction system. Their photoluminescence properties were investigated under long-wavelength UV excitation. The Eu³⁺-doped and Tb³⁺-doped GdCa₃(GaO)₃(BO₃)₄ phosphors efficiently emitted red and green light, respectively. The temperature dependency of emission intensity was measured in a range from room temperature to 150 °C. The emission intensities of the red and green phosphors at 150 °C are 87% and 91% of those at room temperature, respectively. In addition, the decay times of both the red and green phosphors are shorter than 3 ms.     

Luminescent properties of long lasting phosphor Ca2MgSi2O7:Eu

Long afterglow phosphors (Ca_1−xEu_x)₂MgSi₂O₇ (0.002 ≤ x ≤ 0.02) were prepared by solid-state reactions under a weak reductive atmosphere. X-ray diffraction pattern, photoluminescence spectra, decay curve, afterglow spectra and thermoluminescence curves were investigated. The phosphors showed two emission peaks when they were excited by 343 nm, due to two types of Eu²⁺ centers existing in the Ca₂MgSi₂O₇ lattice. However, only one emission peak can be found in their afterglow spectra. Energy transfer between Eu²⁺ ions in inequivalent sites was found. A possible mechanism was presented and discussed. The afterglow decay time of Ca_1.998MgSi₂O₇:Eu_0.002 was nearly 12.5 h which means it was a good long lasting phosphor.     

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.     

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.     

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.     

Upconversion in Er-doped Gd2O3 nanocrystals prepared by propellant synthesis and flame spray pyrolysis

In this study, monoclinic luminescent Gd₂O₃ nanocrystals doped with different concentrations of Er³⁺ (0.1, 1, and 10 mol%) were produced by propellant synthesis and flame spray pyrolysis (FSP). A comparison of their optical and morphological properties is reported. Following 980 nm excitation, an increase of the emission intensity from the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions was observed with increasing Er³⁺ concentration in the Gd₂O₃ nanocrystalline samples prepared via both techniques. However, the overall upconversion emission intensity was greater for the samples obtained by FSP. Furthermore, as the Er³⁺ concentration was increased, the intensity of the red (⁴F_9/2 → ⁴I_15/2) emission was observed to increase more rapidly in comparison to the green (²H_11/2, ⁴S_3/2 → ⁴I_15/2) emission resulting in an overall enhancement of the red component in the upconversion emission. Although both synthetic routes yield average crystallite sizes in the nanoscale, the TEM and SEM images confirm a more homogeneous morphology and lower particle aggregation for the nanocrystals produced by FSP.     

Luminescence properties of Eu ions doped in Y2−xGdxO3 thin films grown by pulsed laser deposition method

Luminescence properties of Y_2−xGd_xO₃:Eu³⁺ (x = 0 to 2.0) thin films are investigated by site-selective laser excitation spectroscopy. The films were grown by pulsed laser deposition method on SiO₂ (100) substrates. Cubic phase Y₂O₃ and Gd₂O₃ and monoclinic phase Gd₂O₃ are identified in the excitation spectrum of the ⁷F₀ → ⁵D₀ transition of Eu³⁺. The emission spectra of the ⁵D₀ → ⁷F_J (J = 1 and 2) transition from individual Eu³⁺ centers were obtained by tuning the laser to resonance with each excitation line. The excitation line at around 580.60 nm corresponds to the line from Eu³⁺ with C₂ site symmetry of cubic phase. New lines at 578.65 and 582.02 nm for the C_S sites of Gd₂O₃ with monoclinic phase are observed by the incorporation of Gd in Y₂O₃ lattice. Energy transfer occurs between Eu³⁺ ions at the C_S sites and from Eu³⁺ ions at the C_S sites to those at the C₂ site in Y_2−xGd_xO₃.     

Photoluminescence properties of RE-activated Na3GdP2O8 (RE = Tb, Dy, Eu, Sm) under VUV excitation

RE³⁺-activated monoclinic Na₃GdP₂O₈ (RE³⁺ = Tb³⁺, Dy³⁺, Eu³⁺, Sm³⁺) phosphors have been synthesized by a solid-state reaction method. Their photoluminescence properties in the vacuum ultraviolet (VUV) region were investigated. By analyzing their excitation spectra, the host-related absorption band was determined to be around 166 nm. The f-d transition bands and the charge transfer bands for Na₃GdP₂O₈:RE³⁺ (RE³⁺ = Tb³⁺, Dy³⁺, Eu³⁺, Sm³⁺) were assigned and corroborated. For the sample Na₃GdP₂O₈:5%Tb³⁺, the strong bands at around 202 and 221 nm are assigned to the 4f-5d spin-allowed transitions and the weak band at 266 nm is related to the spin-forbidden transition of Tb³⁺. For Na₃GdP₂O₈:5%Dy³⁺, the broad band at 176 nm could be related to the f-d transitions of Dy³⁺ and the O²⁻ → Dy³⁺ charge transfer band (CTB) besides the host-related absorption. In the excitation spectrum of Eu³⁺ doped sample, the O²⁻ → Eu³⁺ CTB is observed to be at 245 nm. For the Sm³⁺ doped sample, the O²⁻ → Sm³⁺ CTB is not distinguished obviously and is overlapped with the host-related absorption band.     

White-emitting phosphors Ca6La2Na2(PO4)6F2:Dy and luminescence enhancement through Ce → Dy energy transfer

Ce³⁺ and Dy³⁺ activated fluoro-apatite Ca₆La₂Na₂(PO₄)₆F₂ with chemical formulas Ca₆La_2−xLn_xNa₂(PO₄)₆F₂ (Ln = Ce³⁺, Dy³⁺) were prepared by a solid state reaction technique at high temperature. The vacuum-ultraviolet (VUV) and ultraviolet (UV) spectroscopic properties are investigated. The results indicate that Ce³⁺ ions show the lowest 5d excitation band at ∼305 nm and a broad emission band centered at ∼345 nm. Dy³⁺ ions exhibit intense absorption at VUV and UV range. White-emitting under 172 nm excitation is obtained based on two dominant emissions from Dy³⁺ ions centered at 480 and 577 nm. In addition, the energy transfer from Ce³⁺ to Dy³⁺ in the co-doped samples are observed and discussed.     

Conversion of green emission into white light in Gd2O3 nanophosphors

Gd₂O₃ nanophosphors were prepared by combustion synthesis with and without doping of Dy³⁺ ions. The X-ray powder diffraction patterns indicate that as-prepared Gd₂O₃ and 0.1 mol% Dy₂O₃ doped Gd₂O₃ nanophosphors have monoclinic structures. The transmission electron microscope (TEM) studies revealed that the as-prepared phosphors had an average crystallite sizes around 37 nm. The excitation and emission properties have been investigated for Dy³⁺ doped and undoped Gd₂O₃ nanophosphors. New emission bands were observed in the visible region for Gd₂O₃ nanophosphors without any rare earth ion doping under different excitations. A tentative mechanism for the origin of luminescence from Gd₂O₃ host was discussed. Emission properties also measured for 0.1 mol% Dy³⁺ doped Gd₂O₃ nanophosphors and found the characteristic Dy³⁺ visible emissions at 489 and 580 nm due to ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions, respectively. The chromaticity coordinates were calculated based on the emission spectra of Dy³⁺ doped and undoped Gd₂O₃ nanophosphors and analyzed with Commission Internationale de l'Eclairage (CIE) chromaticity diagram. These nanophosphors exhibit green color in undoped Gd₂O₃ and white color after adding 0.1 mol% Dy₂O₃ to Gd₂O₃ nanophosphors under UV excitation. These phosphors could be a promising phosphor for applications in flat panel displays.     

Preparation, characterization and luminescence of La2TeO6 phosphor doped with Eu

Phosphors of La₂TeO₆ doped with Eu³⁺ ions have been synthesized by the oxidation of the corresponding rare-earths oxytellurides of formula La_2−xEu_xO₂Te (x = 0.02, 0.06, and 0.1) at 1050 K. Powder X-ray diffraction confirms that the as prepared materials consist of the orthorhombic La₂TeO₆ as main phase. The photoluminescence (PL) of red-emitting La_2−xEu_xTeO₆ powder phosphors is reported. The emission spectrum, exhibits an intense emission peak due to ⁵D₀ → ⁷F₂ transition at 616 nm, which indicates that the Eu³⁺ ion occupies a non-centrosymmetric site in the host lattice. These materials could find application for use as lamp phosphors in the red region.     

Intense red-emitting phosphors for LED solid-state lighting

The phosphors Gd_2−xEu_x(MoO₄)₃ (x = 0.20, 0.40, 0.60, 0.80, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0), Gd_0.8−xY_xEu_1.2(MoO₄)₃ (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8) and Gd_0.2Y_0.6−xEu_1.2Sm_x(MoO₄)₃ (x = 0.02, 0.024, 0.028, 0.032, 0.036, 0.04) were prepared by solid-state reaction technique at 950 °C. The presence of the Y³⁺ and Sm³⁺ ions strengthen and broaden the absorption of the phosphors at ∼400 nm. The intense red-emitting phosphor Gd_0.2Y_0.572Eu_1.2Sm_0.028(MoO₄)₃ with orthorhombic structure was obtained. Both Eu³⁺ and Sm³⁺ f-f transition absorptions are observed in the excitation spectra, the main emission line is at 616 nm (⁵D₀ → ⁷F₂ transition of Eu³⁺) and the chromaticity coordinates (x = 0.66, y = 0.33) is very close to the NTSC standard values (x = 0.67, y = 0.33). It is considered to be an efficient red-emitting phosphor for GaN-based light emitting diode (LED).     

Synthesis,characterization and photoluminescence properties of (Gd1−x,Eux)2O2SO4 sub-microphosphors by homogeneous precipitation method

(Gd_1−x,Eu_x)₂O₂SO₄ sub-microphosphors were synthesized by homogeneous precipitation method from commercially available Gd₂O₃, Eu₂O₃, H₂SO₄ and (NH₂)₂CO (urea) starting materials. Fourier transform infrared spectra show that the precursors with different molar ratios of (NH₂)₂CO to Gd₂(SO₄)₃ (the m value) are mostly composed of gadolinium hydroxyl, carbonate and sulfate groups with some crystal water. X-ray diffraction indicated that the precursor (m = 5) can be transformed into pure Gd₂O₂SO₄ phase after heat treated at 900 °C for 2 h in air. Field emission scanning electron microscope micrographs illustrate that the Gd₂O₂SO₄ phosphor particles (m = 5) are quasi-spherical in shape and well dispersed, with a mean particle size of about 300–500 nm. Photoluminescence spectroscopy reveals that the strongest emission peak for (Gd_1−x,Eu_x)₂O₂SO₄ sub-microphosphors is located at 618 nm under 270 nm light excitation, which corresponds to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The quenching concentration of Eu³⁺ ions is 5 mol% and the concentration quenching mechanism is due to the electric dipole–dipole interaction. Decay study reveals that the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions fits with a mono exponential function.     

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.     

Crystal growth and characterization of Yb-doped Gd3Ga5O12

Single crystals of (Yb_xGd_1−x)₃Ga₅O₁₂ (0.0 ≤ x ≤ 1.0) have been grown by the micro-pulling-down method. Formation of continuous solid solutions with a garnet structure was confirmed. Composition dependence of the lattice constant, thermal diffusivity, specific heat capacity and thermal conductivity was investigated. Assignment of the Yb³⁺-energy levels in Gd₃Ga₅O₁₂-host lattice has been performed by using absorption, emission and Raman spectroscopy measurements at both, room temperature and at 12 K.     

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.