Improved optical photoluminescence by charge compensation in the phosphor system CaMoO4:Eu3+

It has been found that charge compensated CaMoO₄:Eu³⁺ phosphors show greatly enhanced red emission under 393 and 467 nm-excitation, compared with CaMoO₄:Eu³⁺ without charge compensation. Two approaches to charge compensation, (a) 2Ca²⁺ → Eu³⁺ + M⁺, where M⁺ is a monovalent cation like Li⁺, Na⁺ and K⁺ acting as a charge compensator; (b) 3Ca²⁺ → 2Eu³⁺ + vacancy, are investigated. The influence of sintering temperature and Eu³⁺ concentration on the luminescent property of phosphor samples is also discussed.     

A novel red phosphor NaLa4(SiO4)3F: Eu

A novel red phosphor NaLa₄(SiO₄)₃F: Eu³⁺ was synthesized by the conventional solid-state reaction at 950 °C for the first time. The luminescence properties of NaLa₄(SiO₄)₃F: Eu³⁺ were investigated, and the critical concentration of the activator concentration (Eu³⁺) was found to be 0.1 mol per formula unit. The phosphor presented red luminescence under the ultraviolet excitation of 254 or 395 nm, attributed to the transitions from ⁵D₀ excited states to ⁷F_J ( J = 0-4) ground states of Eu³⁺ ions. The results indicated that this newly-developed phosphor could find applications in tricolor fluorescent lamp, phosphor-liquid crystal displays and white lighting devices utilizing GaN-based excitation in the near UV.     

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.     

Dynamical processes of energy transfer in red emitting phosphor CaMoO4:Sm, Eu

Upon ⁴K_11/2 excitation of Sm³⁺ at 405 nm, the performance of energy transfer from Sm³⁺ to Eu³⁺ in the red emitting phosphor CaMoO₄:Eu³⁺, Sm³⁺ significantly extends its excitation region for better matching the near-UV LED. Photoluminescence spectra indicate that the energy transfer pathway concerns the relaxation from ⁴K_11/2 to ⁴G_5/2 of Sm³⁺ and subsequent transfer to ⁵D₀ of Eu³⁺ rather than ⁵D₁ of Eu³⁺. The fluorescent decay pattern of Sm³⁺⁴G_5/2 level in CaMoO₄:0.5% Sm³⁺, 2% Eu³⁺ is studied at 77 K based on the Inokuti-Hirayama formula, revealing an electronic dipole-dipole interaction between Sm³⁺ and Eu³⁺. The coefficient for the energy transfer is obtained to be 8.5 × 10⁻⁴⁰ s⁻¹ cm⁶. The fluorescence rise and decay pattern of Eu³⁺⁵D₀ level as Sm³⁺ is only excited at 77 K is well described by the dynamical processes of the energy transfer.     

Enhancement of photoluminescence properties of green to yellow emitting Y3Al5O12: Ce phosphor by AlN addition for white LED applications

AlN-substituted in Y₃Al₅O₁₂: Ce³⁺ phosphor was synthesized to improve the phosphor efficiency of phosphor-converted white light emitting diodes. The photoluminescence properties of AlN-substitued for Al₂O₃ in Y₃Al₅O₁₂: Ce³⁺ phosphor showed excellent green to yellow emission intensity under 460 nm. The highest emission intensity was observed at an AlN concentration of 0.3 mol and a Ce³⁺ concentration in the optimized flux of 0.20 mol. The green to yellow emitting AlN-substituted in Y₃Al₅O₁₂: Ce³⁺ phosphor can be applied to white LEDs.     

Synthesis and photoluminescence properties of Yb doped Ba5(PO4)3Cl phosphor for white light-emitting diodes

Yb²⁺ ion doped Ba₅(PO₄)₃Cl phosphor was synthesized by solid state reaction. Four distinct absorption bands were observed in the Ultraviolet (UV) light region due to the electronic transitions of Yb²⁺ ion from ¹S₀ ground state to ²F_5/2(t_2g), ²F_5/2(e_g), ²F_7/2(t_2g), and ²F_7/2(e_g) excited states. The main emission wavelength of the phosphor was around 630 nm. The optimized Yb²⁺ ion concentration was 0.2 mol% (λ_exc. = 400 nm). The calculated critical distance was about 8.729 Å and the concentration quenching was observed above 0.2 mol% due to the electric dipole–dipole interaction.     

Enhanced red emission in ZnB2O4:Eu by charge compensation

Eu³⁺ doped ZnB₂O₄ without or with different charge compensation (CC) approaches (co-doping Li⁺, Na⁺, K, decreasing the content of Zn²⁺) were prepared by solid state reactions. The phosphors can strongly absorb 393 nm ultraviolet (UV) light which is coupled well with the emission of currently used InGaN-based near UV light emitting diodes (LEDs) and emit red light with a good color purity. The luminescent intensity of phosphors can be remarkably enhanced with any of CC methods. However, the shape and position of excitation and emission spectra keep unchanged. The introduction of Li⁺ can enhance the red emission intensity of Eu³⁺ by ∼4 times with the optimal effect. Red emission of Eu³⁺ can also be enhanced with the other three CC approaches but the effects are not as good as Li⁺ because the volume unbalance in Li⁺ compensation approach is the smallest while net positive charge was offset. The results of this work suggest that volume compensation and equilibrium of mole number should also be taken into account when a CC approaches is selected.     

Synthesis and luminescent properties of SrAl2O4:Eu green-emitting phosphor for white LEDs

SrAl₂O₄:Eu²⁺ phosphor was prepared by a solid-state reaction in CO-reductive atmosphere. X-ray powder diffraction (XRD) analysis confirmed the formation of SrAl₂O₄:Eu²⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated that the microstructure of the phosphor consisted of irregular fine grains with an average size of about 7–8 μm. Photoluminescence measurements showed that the phosphor can be efficiently excited by UV–visible light from 350 to 430 nm, and exhibited bright green emission peaked at about 516 nm. Bright green LEDs were fabricated by incorporating the phosphor with an InGaN-based UV chip. All the characteristics indicated that SrAl₂O₄:Eu²⁺ is a good candidate phosphor applied in white LEDs.     

Synthesis and optical properties of KCaPO4:Eu phosphor

A series of Eu²⁺ doped KCaPO₄ phosphors were prepared by high temperature solid state reaction and an efficient blue-green emission was observed. The photoluminescence (PL) spectrum of the phosphor appeared one asymmetric peak under near-ultraviolet (n-UV) excitation and two emission bands at 480 nm and 540 nm were obtained using Gaussian fit, which was because Eu²⁺ ions inhabited two different Ca²⁺ sites: Eu(I) and Eu(II) in the host lattice, respectively. The excitation spectrum was a broadband extending from 250 to 450 nm, which matched well with the emission of ultraviolet light-emitting diodes (UV LEDs). The effect of Eu²⁺ concentration on the emission intensity of KCaPO₄:Eu²⁺ phosphor was investigated in detail.     

Synthesis and photoluminescence properties of SrLu2O4:Eu superfine phosphor

Superfine powder SrLu₂O₄:Eu³⁺ was synthesized with a precursor prepared by an EDTA - sol-gel method at relatively low temperature using metal nitrate and EDTA as starting materials. The heat decomposition mechanism of the precursor, formation process of SrLu₂O₄:Eu³⁺and the properties of the particles were investigated by thermo-gravimetric (TG) - differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) analyses. The results show that pure SrLu₂O₄:Eu³⁺ superfine powder has been produced after the precursor was calcinated at 900 °C for 2 h and has an elliptical shape and an average diameter of 80-100 nm. Upon excitation with 250 nm light, all the SrLu₂O₄:Eu³⁺ powders show red and orange emissions due to the 4f-4f transitions of Eu³⁺ ions. The highest photoluminescence intensity at 610 nm was found at a content of about 6 mol% Eu³⁺. Splitting of the ⁵D₀-⁷F₁ emission transition revealed that the Eu³⁺ ions occupied two nonequivalent sites in the crystallite by substituting Lu³⁺ ions.     

A yellow-emitting Ca3Si2O7: Eu phosphor for white LEDs

A series of yellow-emitting phosphors based on a silicate host matrix, Ca_3 − xSi₂O₇: xEu²⁺, was prepared by solid-state reaction method. The structure and photoluminescent properties of the phosphors were investigated. The XRD results show that the Eu²⁺ substitution of Ca²⁺ does not change the structure of Ca₃Si₂O₇ host and there is no impurity phase for x < 0.12. The SEM images display that phosphors aggregate obviously and the shape of the phosphor particle is irregular. The EDX results reveal that the phosphors consist of Ca, Si, O, Eu and the concentration of these elements is close to the stoichiometric composition. The Ca_3 − xSi₂O₇: xEu²⁺ phosphors can be excited at a wavelength of 300-490 nm, which is suitable for the emission band of near ultraviolet or blue light-emitting-diode (LED) chips. The phosphors exhibit a broad emission region from 520 to 650 nm and the emission peak centered at 568 nm. In addition, the shape and the position of the emission peak are not influenced by the Eu²⁺ concentration and excitation wavelength. The phosphor for x = 0.045 has the strongest excitation and emission intensity, and the Ca_3 − xSi₂O₇: xEu²⁺ phosphors can be used as candidates for the white LEDs.     

Low temperature synthesis and photoluminescent properties of CaMoO4:Eu red phosphor with uniform micro-assemblies

Scheelite-type Eu³⁺-doped CaMoO₄ red phosphor with uniform micro-assemblies has been successfully synthesized via a facile hydrothermal method at 120 °C for 10 h. The Eu³⁺-doped CaMoO₄ microstructures were assembled by small nanostructures and the morphology of materials was found to be manipulated by dropping different alkalis into the stock solution for the first time. The structure, morphology, and luminescent property were characterized and investigated by techniques of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL). The luminescent investigations confirmed that the Eu³⁺ ions have been effectively doped into CaMoO₄ nanostructures. The successfully achieved Eu³⁺-doped CaMoO₄ nanostructures will be potential in technological applications on near UV chip-based white light emitting diode (WLED).     

Mechanism of energy transfer in Sr2CeO4:Eu phosphor

Blue–white phosphor Sr₂CeO₄ belongs to a particular class of optical materials whose luminescence is governed by optical transitions associated with the electron charge transfer. The originality of its crystallographic structure, a chain-like sequence of luminescent centers, permits an effective transfer of the electronic excitation energy from the host to doped centers. Sr₂CeO₄, рure and doped with Eu³⁺-ions of different concentrations, was synthesized by the Pechini citrate-gel method. The luminescence spectra and luminescence decay curves of Sr₂CeO₄ and Sr₂CeO₄:Eu³⁺ at 300 and 80 K were investigated. The performed experiments revealed the Förster nonradiative energy transfer under the energy migration condition from the crystal host to the doped europium ions.     

A novel blue-emitting Sr3Al2O5Cl2:Ce,Li phosphor for near UV-excited white-light-emitting diodes

A novel blue-emitting Sr₃Al₂O₅Cl₂:Ce³⁺,Li⁺ phosphor has been synthesized by solid state reaction. The excitation spectrum shows a broad band extending from 300 to 400 nm, and the emission spectrum shows a broad blue band peaking at 450 nm with a half width of about 100 nm. The emission intensity at 250 °C remains at about 50% of that at room temperature. The decay curve at the emission peak consists of fast and slow components. The Sr₃Al₂O₅Cl₂:Ce³⁺,Li⁺ should be a promising blue phosphor for near ultraviolet-based white-light-emitting diodes.     

Preparation and luminescence properties of nanocrystalline La2O3:Eu phosphor

Powders La₂O₃ doped with 1 mol% Eu were prepared via a combustion route using different reducers (urea, glycine and citric acid). The structure and morphology were determined with XRD and HRTEM measurement. The main emission positions centered at 626 nm for ⁵D₀ → ⁷F₂ transition are observed. The variation of CT band with different reducers is observed. The intensity of ⁵D₀ → ⁷F₂ transition centered at 626 nm with respect to that of ⁵D₀ → ⁷F₁ transition is a function of the energy difference ΔE between the two CT band positions.     

Luminescent properties of Eu-activated nanophosphors Ca3Y0.8Gd0.2(VO4)2.4(PO4)0.6: Eu for light-emitting diodes

Eu³⁺-doped Ca₃Y_0.8Gd_0.2(VO₄)_2.4(PO₄)_0.6 nanophosphors have been prepared by modified solid-state reaction. X-ray powder diffraction, transmission electron microscopy (TEM), photoluminescence excitation and emission spectra were used to characterize the resulting samples. X-ray powder diffraction (XRD) analysis confirmed the formation of YVO₄. Photoluminescence (PL) results showed that the phosphor could be efficiently excited by UV-visible light from 350 to 550 nm, exhibiting bright orange-red emission(excited by 397) and red emission(excited by 467), which has potential application as a phosphor for UV and blue GaN-based light-emitting diodes (LEDs). TEM images show that the grain size of Ca₃Y_0.45Eu_0.35Gd_0.2(VO₄)_2.4(PO₄)_0.6 is about 39 nm, which is in full agreement with the theoretical calculation data from the XRD patterns.     

Luminescent properties of Eu doped α-Gd2(MoO4)3 phosphor for white light emitting diodes

A novel red emitting phosphor α-Gd₂(MoO₄)₃:Eu³⁺ was developed for white light emitting diodes (LEDs). The phosphor was prepared by solid-state reaction. The effects of the flux content and the activator concentration on the crystal structure, morphology and luminescent properties were investigated by using XRD, SEM, and fluorescent spectra. These results showed that this phosphor can be effectively excited by ultraviolet (UV) (395 nm) and blue (465 nm) light, matching the output wavelengths of ultraviolet or blue LED chips. The α-Gd₂ (MoO₄)₃ phosphor may be a better candidate for solid state lighting application.     

Ca10K（PO4）7:Eu3+红色荧光粉的制备及其发光性质

高温固相法合成了Ca10-xK(PO4)7:xEu3+(x=0.02,0.04,0.06,0.08,0.10,0.12,0.14和0.16)的红色荧光粉。X射线衍射表明,样品具有标准的Ca10K(PO4)7六角晶体结构,且无第二相存在。在393nm的波长激发下,样品获得由Eu3+的4f-4f跃迁产生红光发射,其中以613nm附近的5 D0→7F2电偶极跃迁发射为最强。通过调节Eu3+的掺杂浓度,获得了色坐标与商业化Y2O2S:Eu3+荧光粉十分接近的接近纯色的红色荧光粉。Ca10K(PO4)7:Eu3+是一种可望应用于紫外激发的白光LED的红色荧光粉。     

Hydrothermal synthesis and photoluminescence properties of nano-crystalline GdBO3:Eu phosphor

Nano-crystalline GdBO₃:Eu³⁺ was prepared by a hydrothermal method and the effects of some processing variables such as pH, temperature were investigated. The as-synthesized powders were spherical shaped agglomerates of nanoparticles. The luminescent properties were compared with samples synthesized by conventional solid-state reaction method. Both the photoluminescence intensity and chromaticity were improved and a red-shift in the CT band was observed for the hydrothermally synthesized samples. Possible mechanisms of phase formation were investigated and explanations for the changes in optical properties are proposed.     

CaMoO4:Eu3+纳米荧光粉的尺寸调控及光学性能研究

采用水热法制备了CaMoO₄:Eu³⁺纳米荧光粉.研究了反应温度、反应时间和Eu³⁺掺杂浓度对CaMoO₄:Eu³⁺纳米晶的颗粒尺寸以及光学性能的影响.利用XRD、SEM、FT-IR、UV-Vis和PL对所得样品的相结构、形貌、光学吸收以及发光性能进行了表征.研究结果表明：所合成样品均为四方晶系白钨矿结构的CaMoO₄纳米晶;一方面,随着水热反应温度的降低或者反应时间的缩短,CaMoO₄:Eu³⁺纳米晶都表现出尺寸减小的趋势,荧光强度逐渐减弱,样品的紫外可见光吸收带边发生蓝移;另一方面,随着Eu³⁺掺杂浓度的增加,CaMoO₄:Eu³⁺纳米晶的颗粒尺寸逐渐减小,样品的紫外可见光吸收带边出现红移.同时,在275 nm的光激发下,CaMoO₄:Eu³⁺荧光粉在614 nm处的⁵D₀→⁷F₂跃迁具有最高的荧光强度,观察到红光发射,且发现其荧光猝灭摩尔浓度为6%.