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.     

Photostimulated luminescence in BaX 2 :Eu 2+ (X=Br,Cl) X-ray storage phosphors

The photostimulated luminescence (PSL) effect in BaX 2 :Eu 2+ (X=Br, Cl) is comparable to that observed in BaFBr:Eu 2+ which is used in commercial X-ray storage phosphor screens. After X-irradiation the PSL stimulation spectra of BaX 2 :Eu 2+ (X=Br, Cl) single crystals are identical to the F centre absorption spectra, i.e. the F centres are the PSL-active electron trap centres. The nature of the hole centres is still unknown. The PSL response time of about 0.70 v s is within experimental error of 0.02 v s identical to the Eu 2+ radiative lifetime, whereas in BaCl 2 :Eu 2+ the PSL response time is 0.60 v s, and thus longer than the Eu 2+ radiative lifetime of 0.47 v s.     

一种新型Ca3Mg3Si4O14:Eu2+绿色荧光粉的制备及其性能研究

采用CaCO3,MgO,SiO2,Eu2O3原料,通过高温固相法制备了Ca3Mg3Si4O14:Eu2+荧光粉.通过XRD图谱和PL光谱图,研究了Eu的掺杂浓度与助溶剂(NH4Cl,BaF2)对Ca3Mg3Si4O14:Eu2+荧光粉结构、发光性能和热稳定的影响.XRD图谱对比结果表明,制备的Ca3Mg3Si4O14:Eu2+荧光粉XRD图与理论计算得到的图谱几乎一致.Ca3Mg3Si4O14:Eu2+荧光粉在360～450 nm有很强的激发强度,并且在440 nm激发下发射峰值波长为530 nm的发射光.随着Eu2+离子浓度的增加,发射光谱出现了红移,且在Eu2+离子浓度约为6％时发生了浓度猝灭现象.当添加NH4Cl和BaF2作为助溶剂,Ca3Mg3Si4O14:Eu2+荧光粉的发光强度有一定提高.与未添加助溶剂的Ca3Mg3Si4O14:Eu2+荧光粉的发光强度相比,添加NH4Cl助溶剂后发光强度增加了70％.此外,当温度升高至150 ℃时,Ca3Mg3Si4O14:Eu2+荧光粉和商用绿色荧光粉的发光强度分别降低了7.6％和14％,表明Ca3Mg3Si4O14:Eu2+荧光粉具有良好的热稳定性.这些发光性能均表明Ca3Mg3Si4O14:Eu2+荧光粉是是一种可应用于固态照明的有前景的绿色荧光粉.     

Synthesis and Spectroscopic Properties of GdAl3(BO3)4 Poly-crystals Codoped with Yb3+ and Eu3+

GdAl3(BO3)4 polycrystals co-doped with Yb3+ and Eu3+ has been synthesised by combustion method with urea. Upon the excitation at 465 nm (Eu3+/7F6-->5D2 transition), emission bands centered at 590, 613, 697 and 702 nm in the wavelength region of 550-750 nm have clearly been observed, assigned to the electronic transitions of 5D0-->7FJ (J=1, 2, 4 and 5) of Eu3+ ions, respectively. Meanwhile, an intense emission centred at 980 nm along with a shoulder at 1,040 nm has also been observed by exploiting a cross-relaxation process between the transitions of Eu3+/5D0-->7F6 and Yb3+/2F7/2-->2F5/2. On the contrary, an intense red up-conversion emission centred at 613 nm originated from the 5D0-->7F2 transition of Eu3+ has been observed upon excitation with 980 nm laser diode. The quadratic dependence of the red up-conversion intensity on the pump-laser power reveals a cooperative energy transfer mechanism from a pair of Yb3+ ions to one Eu3+ ion.     

Synthesis and optical characterization of Gd2O3:Eu nanocrystals: surface states and VUV excitation

This paper reports on the synthesis and characterization of Gd₂O₃:Eu³⁺ nanocrystals of different sizes. The particles have been synthesized by a sol-lyophilization process. This methods allows the synthesis of 7–100 nm diameter cubic-phase particles. The photoluminescence properties have been studied with different excitation from X-ray to VUV and visible wavelengths. Compared to the properties of the bulk materials, some important changes on the luminescence are observed. In particular some bands are strengthened when the size of the particles is diminished. We could therefore ascribe this bands to doping ions on a site close to the surface. Also a very low efficiency of excitation for small particles is observed when exciting with X-ray or high-energy VUV photons (i.e. when exciting the host matrix) compared to the efficiency obtained when exciting in the charge transfer band or in the doping ions related states.     

掺杂型BaFBr:Eu2+的热释发光性质的研究

BaFBr:Eu^2 是利用色心存储电子－空穴对并用可见光激励读出存储信息（产生Eu^2 的4f^65d→4f^7的跃迁）的优良的光激励发光材料。通过热释发光技术研究了BaFBr:Eu^2 的热激活行为，对其低温段和高温段的热释发光峰分别进行了归属，通过对BaFBr:Eu^2 以及掺杂Na^ 或Al^3 的BaFBr:Eu^2 的热释发光（TL）谱和光激励发光（PSL）谱的表征，指出在BaFBr:Eu^2 中掺杂Na^ 或Al^3 影响了F（Br^-）色心，使其陷阱深度变涛，并从理论上加以计算，得出的热致激发能量的变化与光致激光能量的变化能很好地吻合。     

Spherical shape with fast decaying property of solvothermally grown (Y,Gd)BO3:Eu nanophosphor

Monodispersed spherical (Y,Gd)BO₃:Eu³⁺ phosphors have been fabricated by a solvothermal method. Each particle is composed of crystalline hexagonal phase primary nanoparticles (∼10 nm in diameter), leading to an abnormal energy-dependent decay behavior, as compared to a micron scale phosphor prepared by the conventional solid-state reaction method. The faster luminescence decay excited under a specific wavelength region making the resultant phosphor suitable for the up-coming display devices, such as 3-dimensional (3D) imaging.     

Effective energy transfer between Ceand Eu in CaAl2Si2O8 host under vacuum ultraviolet illumination

We presented the energy transfer from Ce³⁺ to Eu²⁺ in CaAl₂Si₂O₈ host. The Ce³⁺-doped CaAl₂Si₂O₈ phosphor had a strong emission band at 378 nm under the vacuum ultraviolet (VUV) light. This emission spectrum of Ce³⁺ well overlapped with the excitation spectrum of Eu²⁺ under the UV illumination. As a result, the energy transfer from Ce³⁺ to Eu²⁺ in CaAl₂Si₂O₈ matrix was observed under VUV excitation, which resulted in a significant enhancement of the emission peak intensity at 446 nm. More details about the luminescent properties were presented.     

Nanosize induced effects in luminescent ZnS:Mn2+ quantum dots

Nanocrystals (NCs) of II–VI semiconductors of few nanometers average size, called quantum dots (QDs), are now intensely investigated as radiation detectors. Besides the expected quantum confinement and influence of surface states, our electron paramagnetic resonance investigations of cZnS QDs doped with Mn²⁺ ions, correlated with structural data, underline that other properties should be also taken into consideration in developing the II–VI semiconductor QDs as radiation detectors. Thus, the preferential localization of Mn²⁺ in the core of the cubic ZnS QDs at substitutional Zn²⁺ cation sites next to a stacking lattice defect is expected to lead, besides changes in the impurity energy levels, to specific aggregation properties. An outer shell of different composition can also influence the structural properties of the QDs core with effects on the optical properties as well.     

Cooperative energy transfer and frequency upconversion in Yb3+-Tb 3+ and Nd 3+-Yb 3+-Tb 3+ codoped GdAl3(BO3)4 phosphors

Polycrystalline GdAl₃(BO₃)₄ phosphors codoped with Yb³⁺/Tb³⁺ and/or Nd³⁺/Yb³⁺/Tb³⁺ have been synthesized by combustion method. Upon excitation with a 980 nm laser diode, an intense green upconversion luminescence has been observed in GdAl₃(BO₃)₄:Yb,Tb phosphor. The quadratic dependence of the luminescence on the pump-laser power indicating a cooperative energy transfer process. Meanwhile, it is noticed that upon excitation with 808 nm laser diode, intense luminescence has clearly been detected in GdAl₃(BO₃)₄:Nd,Yb,Tb phosphor. The luminescence intensity exhibits also a quadratic dependence on incident pump-laser power. However, no green-emission has been observed in GdAl₃(BO₃)₄ phosphors codoped with Yb³⁺/Tb³⁺ or Nd³⁺/Tb³⁺ respectively upon excited at 808 nm laser diode. A proposed upconversion mechanism involving energy transfer from Nd³⁺ to Yb³⁺, and then a cooperative energy transfer process from two excited Yb³⁺ to Tb³⁺ has been presented.     

Al3+掺杂BaFBr:Eu2+中F(Br-)心的性质

作为光激励发光的首选材料BaFBr:Eu^2 ，在其中掺杂一定量的Al^3 后，其光激励发光谱向长波方向发生了较大的红移现象，红移的机理是掺杂的Al^3 离子取代了BaFBr:Eu^2）晶格中的Ba^2 离子，且处于F（Br^-）心的次近邻位所致。本文利用喇曼光谱和电子顺磁共振谱对受掺杂Al^3 微扰的F（Br^-)心的结构进行了研究，首次在喇曼光谱的高频移区观测到了由于掺参Al^3 所引起的新结构的产生，通过电子顺磁共振谱表征了在BaFBr:Eu^2＋中Al^3 与F（Br^-）心的相对位置，并且得出F（Br^-)心与OF^-心存在着空间相关性。     

Calcination temperature optimization,energy transfer mechanism and fluorescence temperature dependence of KLa(MoO4)2:Eu3+ phosphors

The optimum calcination temperature for KLa(MoO₄)₂:Eu³⁺ phosphor was confirmed to be 1000 °C via checking the XRD patterns, SEM images and fluorescence spectra for the samples derived from solid state reaction. The energy transfer behavior between Eu³⁺ ions was studied. It was found that electric dipole–dipole interaction is responsible for the fluorescence quenching of ⁵D₂ and ⁵D₁ levels, but exchange interaction is in charge of ⁵D₀ fluorescence quenching. It was also observed that color coordinates of the studied phosphor can be tuned when the doping concentration is relatively low. The fluorescence thermal quenching process was investigated. It was found the thermal quenching followed well crossover model. Judd–Ofelt parameters of Eu³⁺ in KLa(MoO₄)₂ were obtained, and the optical transition properties were further discussed.     

Preparation and luminescence of water soluble poly (N-vinyl-2-pyrrolidone)/LaF3:Eu nanocrystals

Lanthanide-doped luminescent nanocrystals have great potential as biological luminescent labels, but their use has been limited because of most of these nanocrystals are hydrophobic. In this work, water soluble LaF₃:Eu³⁺ down-conversion nanocrystals were prepared by encapsulated individual nanocrystals with polyvinylpyrrolidone (PVP). Their morphology, surface structure and luminescence properties were explored in detail. The results indicate that these nanocrystals can be readily dispersed in water, forming a stable and transparent colloidal solution. The colloidal solution displayed unique red luminescence with high emission intensity under ultraviolet excitation. These results suggest that these nanocrystals have great potential as luminescent labeling materials for biological applications.     

Crystal-Size Dependence of Replenishment Effect in BaFBr:Eu

Excitation spectra of photo-stimulated luminescence (PSL) in BaFBr:Eu and BaFBr:Eu ? Na crystals were studied. Replenishment of PSL at liquid helium temperature was investigated in crystals of various sizes including a commercially available X-ray storage phosphor plate (Image Plate). Although a weak replenishment effect was observed in the fine powder crystals, no replenishment effects were observed in Image Plate, while it showed strong PSL at liquid helium temperature. Results indicate that there are two types of PSL centers, one consists of spatially correlated electrons and holes and the other consists of electrons and holes trapped at isolated centers. Lack of the replenishment effect in Image Plate indicates that trapped electrons are stabilized by the surface and need thermal activation to recombine with holes which are possibly trapped at doped Eu^2?.     

Fabrication of red-emitting CaAlSiN3: Eu2+ through phosphor-in-glass approach for application in rear combination lamp

In this study, the red-emitting phosphor-in-glass (PiG) using the CaAlSiN₃: Eu²⁺ (CASN) phosphor is reported for the first time. The CASN: Eu²⁺ PiG samples with a maximum luminous flux of 25.1–29.4 for l minute at laser power of 1 W/mm² was obtained using a low-temperature glass frit and GPS furnace. Despite the increase in the phosphor from 15 to 25 wt%, the PiG produced at low temperature of 380 °C showed robust properties. Finally, the red PiG module designed for rear lamp applications maintains over 90% lumens for a minute at 350 mA and achieves an intense red light having a color temperature of 4589 K.     

The photoluminescent properties of Eu in MgO-Ga2O3-SiO2 nanocrystalline glass-ceramic

The MgO-Ga₂O₃-SiO₂ glass-ceramic (GC) containing MgGa₂O₄ nanocrystals and glasses doped with Eu³⁺ ions were prepared by the sol-gel method. The down-conversion and up-conversion luminescence (UCL) properties were studied. The results indicated that the relative intensity of f-f transitions of Eu³⁺ decreased in contrast with that of charge transfer (CT) absorption with the increase in heating temperature. Using a Xe lamp and 800 nm femtosecond (fs) laser excitation, strong red luminescence of Eu³⁺ in MgO-Ga₂O₃-SiO₂ glasses and GC was observed.     

电子俘获光存储材料BaLiF3:Eu2+的光激励发光及光存储性质研究

利用高温固相反应法制备了混晶状的BaLiF3:Eu2 样品.其紫外光激发的发射峰与光激励发光峰均在410 nm处,属于Eu2 的5d-4f跃迁发光.光激励峰位于660 nm,因而可以配用简单廉价的氦氖激光器.根据光谱特征给出了光激励发光的简单机理.测量了该材料光激励发光衰减性能,结果表明BaLiF3:Eu2 存储的信息可以方便地擦除掉.该材料具有优良的光激励发光特性,是一类很有发展前途的电子俘获光存储材料.     

A potential reddish orange emitting phosphor Ca2BO3Cl:Eu for white light-emitting diodes

A series of phosphors Ca₂BO₃Cl:Eu³⁺ were synthesized by using a high-temperature solid-state reaction technique, and their UV–vis luminescence properties were investigated. The f–f transitions of Eu³⁺ in the host lattice were assigned and discussed. The excitation and emission spectra indicate that this phosphor can be effectively excited by ultraviolet (394 nm), and exhibit reddish orange emission corresponding to the ⁵D₀→⁷F_J (J=0, 1, 2) transitions of Eu³⁺. The influence of the doping concentration and charge compensators on the relative emission intensity of Eu³⁺ was investigated, and the optimum doping concentration is 0.04. The critical distance R_c was estimated to be 17.1 Å in terms of the concentration quenching data. The present study suggests that Ca₂BO₃Cl:Eu³⁺ can be a potential candidate as an UV-convertible phosphor for white light-emitting diodes (LEDs).     

KGd(MoO4)2:Eu as a promising red phosphor for light-emitting diode application

A red phosphor KGd(MoO₄)₂:Eu³⁺ was prepared by solid-state reaction technique at high temperature. Its photoluminescent property was investigated and the optimum concentration of Eu³⁺ doped in the KGd(MoO₄)₂ is 25 mol%. Compared with Y₂O₂S:0.05Eu³⁺, the obtained KGd(MoO₄)₂:Eu³⁺ shows wider excitation band around 400 nm, higher intensity of Eu^{3+ 5}D₀–⁷F₂ emission upon excitation 393 nm, and the CIE chromaticity coordinates (x = 0.655, y = 0.345) are closer to the standard of National Television Standard Committee (NTSC). The optical properties of KGd(MoO₄)₂:Eu³⁺ suggest that it is an efficient red-emitting phosphor for light-emitting diode applications.