Luminescence properties of Eu- and Mg-doped LiTaO3 obtained via the polymeric precursor method

This work reports the pure lithium tantalate (LiTaO₃), europium (III)-doped LiTaO₃ and magnesium (II)-europium (III)-doped LiTaO₃ preparation by the polymeric precursor method, using four different powered samples of Eu³⁺ ion concentrations 0.1 and 1 at%, observing their effect on the luminescent property of the material. Results indicated LiTaO₃ phase free of secondary phases at 650 °C and the photoluminescence (PL) emission spectra showed the characteristic sharp emission bands given by Eu³⁺ ions when they are excited at a wavelength of 399 nm. An increase of dopants led us to a non-homogeneous broadening and showed a slightly larger one when Mg was added. A displacement of the transition ⁵D₀→⁷F₀ to shorter wavelengths as function of Eu³⁺concentration was also noticed.     

Long lasting phosphorescence of Eu in reduced SrO-B2O3 glasses

The blue long-lasting phosphorescence (LLP) phenomenon was observed for Eu²⁺-doped SrO-B₂O₃ glasses prepared in the reducing atmosphere. The phosphorescence peaks at about 450 nm due to the 4f5d→4f transition of Eu²⁺. With the doping of different amounts of Eu²⁺, the concentration-quenching phenomenon was observed for both the LLP and photoluminescence of the glasses, and the critical concentration for the two cases was same, i.e., 0.02 mol% Eu²⁺. And by the investigation of the TL curves, the content of Eu²⁺ had an effect on the trap depth of the samples. At last the possible mechanism of the LLP of the samples was suggested.     

Potential PDP phosphors with strong absorption around 172 nm: Rare earth doped NaLaP2O7 and NaGdP2O7

NaLaP₂O₇ and NaGdP₂O₇ powder samples are prepared by solid-state reactions at 750 and 600 °C, respectively, and the VUV-excited luminescence properties of Ln³⁺ (Ln=Ce, Pr, Tb, Tm, Eu) in both diphosphates are studied. Ln³⁺ ions in both hosts show analogous luminescence. For Ce³⁺-doped samples, the five Ce³⁺ 5d levels can be clearly identified. As for Pr³⁺ and Tb³⁺-doped samples, strong 4f-5d absorption band around 172 nm is observed, which matches well with Xe-He excimer in plasma display panel (PDP) devices. As a result, Pr³⁺ can be utilized as sensitizer to absorb 172 nm VUV photon and transfer energy to appropriate activators, and Tb³⁺-doped NaREP₂O₇(RE=La, Gd) are potential 172 nm excited green PDP phosphors. For Tm³⁺ and Eu³⁺-doped samples, the Tm³⁺-O²⁻ charge transfer band (CTB) is observed to be at 177 nm, but the CTB of Eu³⁺ is observed at abnormally low energy position, which might originate from multi-position of Eu³⁺ ions. The similarity in luminescence properties of Ln³⁺ in both hosts indicates certain structural resemblance of coordination environment of Ln³⁺ in the two sodium rare earth diphosphates.     

Blue light emission from Eu ions in sol-gel-derived Al2O3-SiO2 glasses

Blue light-emitting glasses were successfully prepared by doping Eu²⁺ ions in the system Al₂O₃-SiO₂. The Al₂O₃-SiO₂ glasses doped with Eu³⁺ ions were synthesized using a sol-gel method, followed by heating in hydrogen gas atmosphere to reduce into the Eu²⁺ ions. The obtained glasses exhibited emission spectra with peak at ∼450 nm due to 4f⁶5d→4f⁷ (⁸S_7/2) transition, the intensities of which strongly changed depending on their glass composition and heating conditions. The emission quantum efficiency of 48% was achieved by heating the glass with the ratio of Al³⁺ to Eu³⁺ at about 6 at 1000 °C in hydrogen gas atmosphere. It was found that the Al₂O₃-SiO₂ glasses were appropriate not only for homogeneously doping the Eu³⁺ ions in glass structure but also reducing to Eu²⁺ ions, resulting in enhanced blue light-emission properties.     

Thermoluminescence of rare earth activated CdSO4, SrSO4 and BaSO4

The thermoluminescence (TL) of rare earth (RE) activated sulfates of Cd, Sr and Ba was studied above room temperature. Many of the phosphors prepared exhibit an extremely bright TL following X-irradiation (most notably with Sm, Eu, Tb, Dy and Tm dopants), having an efficiency comparable to that of the highest sensitivity phosphors available for TL dosimetry, and exhibiting activator-induced glow peaks between 405 and 480°K. In a given lattice, the RE³⁺ ions produce a characteristic glow peak at the same temperature (independent of the particular RE ion), whereas Eu²⁺ produces a single glow peak at a different temperature. A decrease in glow peak temperature with increasing interatomic spacing was observed in the homologous SrSO₄-BaSO₄ system - this shift being most pronounced in the Eu²⁺ -doped materials. TL emission spectra were obtained for trivalent Sm, Tb, Dy and Tm and for divalent Eu in these sulfates (and also in CaSO₄).     

Hydrothermal synthesis of Sb doped and (Sb, Eu) co-doped YBO3 with nearly white light luminescence

Sb³⁺-doped, Eu³⁺-doped and (Sb³⁺, Eu³⁺) co-doped YBO₃ crystals have been synthesized using Y₂O₃, B₂O₃, SbCl₃ and Eu₂O₃ as raw materials through a hydrothermal method. Phase-pure YBO₃ crystal with hexagonal flake shape has been synthesized at 473 K for 3 days. The photoluminescent property of YBO₃ with different activators were investigated using luminescent spectrometer at room temperature. The color of the (Sb³⁺, Eu³⁺) co-doped YBO₃ crystal could be controlled from blue to red by changing the Sb³⁺/Eu³⁺ ratio in the initial reactants. The nearly white emission could be obtained through changing the Sb³⁺/Eu³⁺ ratio in reaction.     

KBaPO4:Ln (Ln=Eu, Tb, Sm) phosphors for UV excitable white light-emitting diodes

This letter reports the novel three emission bands based on phosphate host matrix, KBaPO₄ doped with Eu²⁺, Tb³⁺, and Sm³⁺ for white light-emitting diodes (LEDs). The phosphors were synthesized by solid-state reaction and thermal stability was elucidated by measuring photoluminescence at higher temperatures. Eu²⁺-doped KBaPO₄ phosphor emits blue luminescence with a peak wavelength at 420 nm under maximum near-ultraviolet excitation of 360 nm. Tb³⁺-doped KBaPO₄ phosphor emits green luminescence with a peak wavelength at 540 nm under maximum near-ultraviolet excitation of 370 nm. Sm³⁺-doped KBaPO₄ phosphor emits orange-red luminescence with a peak wavelength at 594 nm under maximum near-ultraviolet excitation of 400 nm. The thermal stabilities of KBaPO₄:Ln (Ln=Eu²⁺, Tb³⁺, Sm³⁺), in comparison to commercially available YAG:Ce³⁺ phosphor were found to be higher in a wide temperature range of 25-300 °C.     

Abnormally enhanced Eu emission in Y2O2SO4:Eu inherited from their precursory dodecylsulfate-templated concentric-layered nanostructure

A new nanostructure-mediated approach was demonstrated to synthesize Eu³⁺-doped yttrium oxysulfates Y₂O₂SO₄:Eu³⁺ giving rise to abnormally enhanced Eu³⁺ emission. Yttrium and europium salts, sodium dodecylsulfate (SDS), and urea at various Eu³⁺ concentrations were reacted in aqueous solution at 80, 85, and 87 °C to yield Eu³⁺-doped dodecylsulfate-templated yttrium oxide mesophases with straight-layered (S-type), concentric-layered (C-type) and layer-to-hexagonal transient-layered (T-type) structures, respectively. On calcination at 1000 °C, all of these mesophases were converted into Y₂O₂SO₄:Eu³⁺ to exhibit luminescence bands including the ⁵D₀-⁷F₂ transition with a tendency in intensity to saturate or reach a maximum at 10-12 mol% Eu doping. The Eu³⁺ emissions for Y₂O₂SO₄:Eu³⁺ mediated by the T- and C-type mesophases were enhanced in intensity by a factor of about two and three times, respectively, stronger than those for not only compositionally the same sulfate Y₂O₂SO₄:Eu³⁺ obtained from yttrium-based sulfates but also Y₂O₃:Eu³⁺ obtained in the SDS-free system. In contrast, the emission intensities for the S-type-mesophase-mediated Y₂O₂SO₄:Eu³⁺ were close to those for the latter sulfates. The abnormally enhanced emission is likely based on specific deformation of sulfate groups induced through the conversion of concentric dodecylsulfate-layers to straight sulfate-layers in the oxysulfate framework upon calcination.     

Probing of inversion symmetry site in Eu-doped GdPO4 by luminescence study: Concentration and annealing effect

Eu³⁺-doped gadolinium orthophosphate (GdPO₄) (Eu³⁺ at%=0, 2, 5, 7, 10, 15, 20 and 30) nanoparticles have been prepared by ethylene glycol route and subsequently heated at 500 and 900 °C. The crystallite size increases with increasing heat-treatment temperature. Luminescence study shows that magnetic dipole transition (⁵D₀→⁷F₁) is prominent over the electric dipole transition (⁵D₀→⁷F₂), which has been attributed to occupancy of inversion symmetry site by more Eu³⁺ ions in Eu³⁺-doped GdPO₄. The luminescence intensity is enhanced as heat-treatment temperature increases from 500 to 900 °C due to the improved crystallinity. Optimum luminescence is observed for 5–7 at% Eu³⁺ in GdPO₄ nanoparticles. Above this concentration, luminescence intensity decreases due to concentration quenching effect. This is supported by lifetime study.     

Eu photoluminescence enhancement due to thermal energy transfer in Eu2O3-doped SiO2-B2O3-PbO2 glasses system

In this work, Eu³⁺-doped lead borosilicate glasses (SiO₂-B₂O₃-PbO₂) synthesized by fusion method had their optical properties investigated as a function of temperature. Atomic Force Microscopy images obtained for a glass matrix annealed at 350 and 500 °C show a precipitated crystalline phase with sizes 11 and 21 nm, respectively. Besides, as the temperature increases from 350 to 300 K a strong Eu³⁺ photoluminescence (PL) enhancement takes place. This anomalous feature is attributed to the thermally activated carrier transfer process from nanocrystals and charged intrinsic defects states to Eu³⁺ energy levels. In addition, the PL peaks in this temperature range were assigned to the Eu³⁺ transitions ⁵D₀→⁷F₂, at 612 nm, ⁵D₀→⁷F₁, at 595 nm, and ⁵D₀→⁷F₀, at 585 nm. It was also observed that the ⁵D₀→⁷F₃ and ⁵D₀→⁷F₄ PL bands at 655 and 700 nm, respectively, show a continuous decrease in intensity as the temperature increases.     

Orange emission enhancement by energy transfer in Sr3Al2O5Cl2:Ce, Eu phosphor for solid-state lighting

Orange-emissive Ce³⁺/Eu²⁺ co-doped Sr₃Al₂O₅Cl₂ phosphors were synthesized by a solid-state reaction. The large overlap between the emission spectrum of blue Sr₃Al₂O₅Cl₂:Ce³⁺ and the excitation spectrum of orange Sr₃Al₂O₅Cl₂:Eu²⁺, and the shortening trend in lifetime of Ce³⁺ donors with increasing Eu²⁺ concentration in Sr₃Al₂O₅Cl₂:Ce³⁺, Eu²⁺ provide the strong evidence of energy transfer from Ce³⁺ to Eu²⁺ ions. It supports that the orange emission intensity of the optimal co-doped phosphor is 1.5 times stronger than that of single Eu²⁺-doped one. The Sr₃Al₂O₅Cl₂:Ce³⁺, Eu²⁺ phosphor is a promising orange-emitting phosphor for warm-white-light-emitting diode because of its effective excitation in the near ultraviolet range.     

Novel red perovskite phosphor Ca2AlNbO6:Eu for white light-emitting diode application

Eu³⁺-doped perovskite phosphors of Ca₂AlNbO₆ were synthesized from a solid state reaction. A small amount of the Li₂CO₃ flux was found to greatly shorten calcination time and reduce reaction temperature. The structural and optical properties of the samples were systematically investigated. The excitation spectra of Ca₂AlNbO₆:Eu³⁺ reveal two excitation bands at 398 (⁷F₀→⁵L₆) and 466 nm (⁷F₀→⁵D₂), which match well with the two popular emissions from near-UV and blue LED chips. Under blue light excitation, the red emission of Ca₂AlNbO₆:0.05Eu³⁺ is twice more intense than that of (Y_0.95Eu_0.05)₂O₃. The chromaticity coordinates of (Ca_0.95Eu_0.05)₂AlNbO₆ (x=0.654, y=0.346) are close to the standard values (x=0.670, y=0.330) of National Television Standard Committee (NTSC). The optical properties suggest that Ca₂AlNbO₆:Eu³⁺ is an efficient red-emitting phosphor for light-emitting diode applications.     

白光LED用LiBaBO3:Eu2+材料发光特性研究

采用高温固相法制备了LiBaBO₃:Eu²⁺绿色发光材料.测量了Eu²⁺浓度为1mol%时样品的激发与发射光谱,其发射光谱为双峰宽谱,主峰分别为482和507nm,与理论计算值符合很好;监测482nm发射峰时,对应激发光谱的峰值为287和365nm,监测507nm发射峰时,对应的激发峰为365和405nm.研究了Eu²⁺浓度对材料发射光谱的影响,结果显示,随Eu²⁺浓度的增大,蓝、绿发射峰均发生了     

Luminescence studies on ZnO-P2O5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Zinc phosphate glasses doped with Gd₂O₃:Eu nanoparticles and Eu₂O₃ were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P₂O₅ glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu³⁺ ions has been observed when Eu₂O₃ is incorporated in ZnO-P₂O₅ glasses. Lack of energy transfer from these defect centres to Eu³⁺ in Gd₂O₃:Eu nanoparticles doped ZnO-P₂O₅ glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu³⁺ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd₂O₃:Eu nanoparticles or Eu₂O₃ incorporation.     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu³⁺ ions.     

Photoluminescent properties of Eu 3 +(Dy 3 +)-activated YNb x Ta 1 - x O 4 and REVTa 2 O 9 (RE?=?Y, La, Gd) phosphors from the hybrid precursors

In the context, Eu³⁺ (Dy³⁺)-doped YNb_xTa_1-xO₄ and REVTa₂O₉ (RE=Y, La, Gd) phosphors have been synthesized from the hybrid precursors. Both XRD and SEM indicated the particles present good crystalline state, whose crystalline grain sizes were in the range of 0.5 to 1 μm. Besides, XRD patterns of YNb_xTa_1-xO₄ (x=0.1, 0.2, 0.3, 0.5, 0.9) have shown that the phase has been changed from M^′-type YTaO₄ to M-type YNbO₄ with increasing niobium content. Furthermore, from the luminescent spectra of Eu³⁺-doped YNb_xTa_1-xO₄, it was observed that the ⁵ D ₀–⁷ F ₂ transition of Eu³⁺ was predominated and its intensity increases with increasing niobium content, as well as the intensity ratio of ⁵ D ₀–⁷ F ₂ transition to ⁵ D ₀–⁷ F ₁ transition for Eu³⁺. The optimum concentrations of Eu³⁺ and Dy³⁺ in YNb_0.5Ta_0.5O₄ have been found to be 6 and 5 mol %, respectively. At the same time, the luminescent properties of Eu³⁺ and Dy³⁺ in REVTa₂O₉ (RE=Y, La, Gd) have also been investigated that GdVTa₂O₉:Eu³⁺ (Dy³⁺) presents high luminescence, while LaVTa₂O₉:Eu³⁺ (Dy³⁺) shows weak luminescence. PACS 78.20.-e; 78.55.-m; 61.72.Ss; 32.50.+d; 81.40 Tv     

Self-assembled CaMoO4 and CaMoO4:Eu hierarchical superstructures: Facile sonochemical route synthesis and tunable luminescent properties

Tetragonal CaMoO₄ and CaMoO₄:Eu³⁺ with various novel three-dimensional (3D) hierarchical architectures were successfully synthesized via a facile, efficient sonochemistry process in the absence of any surfactant or template. XRD, EDS, FE-SEM, and photoluminescence (PL) were employed to characterize the as-obtained products. It was found that morphology modulation could be easily realized by changing pH value of the precursor. The pH value of the precursor not only affected the substructures of the hierarchical structures, but also determined the size distributions of the final products. The formation mechanism for different hierarchical architectures was proposed on the basis of time-dependent experiments. The luminescence spectra showed that CaMoO₄:Eu³⁺ phosphors can be effectively excited by the near ultraviolet (UV) (396 nm) and blue (466 nm) light, and exhibited strong red emission around 615 nm, which was attributed to the Eu³⁺⁵D₀→⁷F₂ transition. Compared with Y₂O₃:Eu³⁺ phosphor, CaMoO₄:Eu³⁺ is much more stable, efficient and suitable, therefore, this phosphors could be a promising red component for possible applications in the field of LEDs.     

A potential red phosphor LiGd(MoO4)2:Eu for light-emitting diode application

Eu³⁺-doped LiGd(MoO₄)₂ red phosphor was synthesized by solid-state reaction, and its photoluminescent properties were measured. The effect of Eu³⁺ doping concentration on PL intensity was investigated, and the optimum concentration of Eu³⁺ doped in LiGd(MoO₄)₂ was found to be 30 mol%. Compared with Y₂O₂S:0.05Eu³⁺, Na_0.5Gd_0.5MoO₄:Eu³⁺ and KGd(MoO₄)₂:Eu³⁺, the LiGd(MoO₄)₂:Eu³⁺ phosphor showed a stronger excitation band around 395 nm and a higher intensity red emission of Eu³⁺ under 395 nm light excitation. For the first time, intensive red light-emitting diodes (LEDs) were fabricated by combining phosphor and a 395 nm InGaN chip, confirming that the LiGd(MoO₄)₂:Eu³⁺ phosphor is a good candidate for LED applications.     

Photoluminescence of (Ba1−xEux)Si6N8O (0.005≤x≤0.2) phosphors

Eu²⁺-doped BaSi₆N₈O phosphors (Ba_1−xEu_xSi₆N₈O, 0.005≤x≤0.2) were synthesized by gas-pressure sintering of the powder mixture of BaCO₃, Si₃N₄, and Eu₂O₃ at 1750 °C under 0.5 MPa N₂. The fired powder consists of a major BaSi₆N₈O phase and a trace amount of impurity phases. The structural result of the BaSi₆N₈O powder, refined by the Rietveld method, agrees well with that of single crystals. A wide blue luminescence band peaking at about 500 nm is observed in BaSi₆N₈O:Eu²⁺, upon excitation with the ultraviolet light of 310 nm. Although Eu is covalently bonded to six nearest neighbor nitrogen atoms, the luminescence of Eu²⁺ is not significantly redshifted but shows a very narrow excitation spectrum at high energies. The origin of the short-wavelength luminescence is mainly ascribed to a small crystal-field splitting as a result of extremely long distances between europium and nitrogen ligands in BaSi₆N₈O:Eu²⁺.     

Luminescent properties of green- or red-emitting Eu-doped Sr3Al2O6 for LED

Eu²⁺-doped Sr₃Al₂O₆ (Sr_3−xEu_xAl₂O₆) was synthesized by a solid-state reaction under either H₂ and N₂ atmosphere or CO atmosphere. When H₂ was used as the reducing agent, the phosphor exhibited green emission under near UV excitation, while CO was used as the reducing agent, the phosphor mainly showed red emission under blue light excitation. Both emissions belong to the d-f transition of Eu²⁺ ion. The relationship between the emission wavelengths and the occupation of Eu²⁺ at different crystallographic sites was studied. The preferential substitution of Eu²⁺ into different Sr²⁺ cites at different reaction periods and the substitution rates under different atmospheres were discussed. Finally, green-emitting and red-emitting LEDs were fabricated by coating the phosphor onto near UV- or blue-emitting InGaN chips.