Luminescence Properties of （ Y, Gd） Al3 （BO3） 4 ： Eu^3＋ under VUV excitation

(Y, Gd)Al3 (BO3)4:Eu^3 samples were prepared by the conventional solid state reaction. The XRD results indicate that the crystal symmetry is low. The excitation spectrum is composed of two broad bands centered at about 170 and 250 nm respectively. In the emission spectra, the peak wavelength is about 616 nm under 147 nm VUV excitation. The luminescent chromaticity coordinate and the relative intensity change along with Gd^3 mole concentration in the range of 0.15 to 0.85 mol (and Eu^3 mole concentration, 0.02 to 0. 1 mol). The correlative data show that the concentration quenching occurs when the Eu^3 mole concentration ranges from 0.02 to 0.1 mol, and the Gd^3 →Gd^3 , Gd^3 →Eu^3 and host→Eu^3 , Gd^3 energy transfers exist, and Gd^3 mole concentration influences Eu^3 emission.     

Luminescent properties of Ca2SiO4：Eu^3＋ red phosphor for trichromatic white light emitting diodes

The luminescent properties of Eu^3＋doped Ca2SiO4 red phosphors synthesized by the flux fusion reaction method were investigated. It was found that the excitation spectrum included two regions： the weak excitation band below 325 nm and strong narrow peaks above 325 nm. The main peak of the excitation band was located at 400 nm. The peaks located at 290 nm were assigned to the combination of the charge transfer transition of O-Eu, peaks above 325 nm （325, 385, 400, 470, 511, and 539 nm） were assigned to the f-f transitions of Eu^3＋. The emission spectrum was dominated by the red peak located at 612 nm due to the electric dipole transition of ^5D0-^7F2. In addition, the effects of the Eu^3＋ content and charge compensators of Li^＋, Na^＋, K^＋, and Cl^- ions on the emission intensity were investigated. The experiment results suggested that the strongest emission was obtained when the concentration of the Eu^3＋ ions was 0.3 mol^-1, and Li^＋ ions gave the best improvement to enhance the emission intensity. Ca2SiO4：Eu^3＋, Li^＋ was thus suitable for low-cost trichromatic white light emitting diodes （WLED） based on UV InGaN chip.     

Photoluminescent properties of Ca2Gd8（SiO4）6O2： Dy^3＋ phosphor films prepared by sol-gel process

There are growing interests on phosphor thin films owing to their potential application in high-resolution devices such as cathode ray tubes and flat panel display devices. The solution-based sol-gel method is one of the most important techniques for the synthesis of various functional coating films. Compounds with the apatite structure are very suitable host lattices for various luminescent ions. Ca2RE8（SiO4）6O2 （ RE=Y, Gd, La ） is a kind of ternary rare-earth-metal silicate with oxyapatite structure, which has been used as host material for the luminescence of various rare earth and mercury-like ions. In this article, Ca2Gd8（SiO4）6O2：Dy^3＋phosphor films were dip-coated on quartz glass substrates through the sol-gel process. X-ray diffraction （XRD）, atomic force microscopy （AFM）, photoluminescence （PL） spectra, as well as lifetimes were used to characterize the resulting films. AFM study revealed that the phosphor films consisted of homogeneous particles. The Dy^3＋ showed its characteristic emission in crystalline phosphor films, i.e., ^4F9/2-^6H15/2 and ^4F9/2-^6H13/2.     

Photoluminescence of SrGdGa3O7：RE（RE=Ce^3＋, Pr^3＋ ,Tb^3＋） under VUV-UV Excitation

SrGdGa3O7:RE(RE=Ce^3 ,Pr^3 ,Tb^3 ) were prepared by traditional solid-state reaction and their luminescence properties in the range of VUV-Vis were investigated. The two broad bands situated at about 177 and 217nm in excitation spectra are attributed to the host lattices absorption, and they have no considerable change when doped different rare earth ions. The f-d transitions of Pr^3 and Tb^3 calculated by the formula gathered by Dorenbos were compared to the experimental results. The excitation spectra also show the sharp Gd^3 excitation line at about 274 nm pointing to an efficient energy transfer from Gd^3 to Pr^3 and Tb^3 . All of the emission spectra present the characteristic emissions of rare earth ions when excited by VUV and UV.     

Study on Spectra of La2CaB10O19：Eu^3＋ in VUV-VIS Range

Excitation and emission spectra of new borate La2CaB10O19 doped Eu^3 in VUV-VIS range, high resolution emission spectra at room temperature and lifetime of Eu^3 were investigated. The emission line at about 616nm attributed to the ^5D0-^7F2 transition of Eu^3 is the most intense emission of Eu^3 . The broad band at about 244nm is originated from charge transition band (CTB) of O^2→Eu^3 . According to the numbers of spectral lines ^5D0-^7F0 and ^5D0-7F1 in highresolution spectrum, Eu^3 ions occupy two crystallographic sites. The lifetimes of ^5D0-^7F0 transition of Eu^3 of two kinds of lattice sites are individually 2.1 and 2.6ms, and both are exponential decay. In the VUV excitation spectrum, complicated band between 130 and 170nm consists of host absorption and f-d transition of Eu^3 .     

Luminescent properties of Eu~（3＋） doped Gd_2WO_6 and Gd_2（WO_4）_3 nanophosphors prepared via co-precipitation method

Eu3+ doped Gd2WO6 and Gd2(WO4)3 nanophosphors with different concentrations were prepared via a co-precipitation method. The structure and morphology of the nanocrystal samples were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The emission spectra and excitation spectra of samples were measured. J-O parameters and quantum efficiencies of Eu3+ 5D0 energy level were calculated, and the concentration quenching of Eu3+ luminescence in different matrixes were studied. The results indicated that effective Eu3+:5D0-7F2 red luminescence could be achieved while excited by 395 nm near-UV light and 465 nm blue light in Gd2WO6 host, which was similar to the familiar Gd2(WO4)3:Eu. Therefore, the Gd2WO6:Eu red phosphors might have a potential application for white LED.     

Preparation, Structural Analysis and Luminescence Properties of Nanocrystalline Phosphor Gd203 ： Eu

Nanocrystalline monoclinic and cubic Gd2O3:Eu with different Eu^3 concentration were prepared using glycinenitrate combustion synthesis. By changing the ratio of glycine to nitrate and proper heat treatment, pure monoclinic and cubic Gd203:Eu with particle size less than 40 nm can be easily formed. Under ultraviolet excitation, main emission of Eu^3 (^5D0→^7F2) locates at 624 nm in monoclinic Gd2O3:Eu and 611 nm in cubic sample, In excitation spectrum two broad bands corresponding to the host absorption and charge transfer state (CTS) and f-f transitions of Gd^3 and Eu^3 were observed and discussed. The quenching concentration of monoclinic and cubic Gd2O3:Eu is 10% and 15 %, respectively,both of which are much higher than that of bulk Gd2O3 : Eu.     

Eu2＋ and Dy3＋ codoped （Ca,Sr）7（SiO3）6Cl2 highly efficient yellow phosphor

Eu2+ and Dy3+ codoped(Ca,Sr)7(SiO3)6Cl2 yellow phosphors were successfully synthesized by self-flux method. The structure, morphology and photoluminescence properties were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM) and photoluminescence spectra. The as-prepared phosphor showed a broad emission spectrum centered at 550 nm for Eu2+single-doped phosphor, while located at 548–544 nm for the Eu2+, Dy3+ codoped samples under excitation at 380 nm light. The emission intensity was greatly improved when Dy3+ was doped into the(Ca,Sr)7(SiO3)6Cl2:Eu2+ system. The composition-optimized sample with 3 mol.% of Dy3+ and constant 10 mol.% of Eu2+ exhibited a 220% PL enhancement compared to the phosphor with 10 mol.% Eu2+ single-doped. Meanwhile, it was found that the quantum efficiency of phosphor namely(Ca,Sr)7(SiO3)6Cl2:3 mol.% Dy3+, 10 mol.% Eu2+ could get up to 24.6%. The synthesized yellow-emitting(Ca,Sr)7(SiO3)6Cl2:Dy3+,Eu2+ is a promising candidate as high-efficiency yellow phosphor for NUV-excited white LEDs.     

Luminescence of Eu^3 ＋ in LnAlO3 （Ln = Gd, Y） under UV and VUV Excitation

Single phases of LnAlO3 : Eu^3 ( Ln = Gd, Y ) were obtained by the process of evaporation of their nitric acid solution, and then pyrolysis of their nitrate salts. On monitoring by 613 nm emission, broad bands at around 270 and 170nm were observed in the excitation spectrum of Gd0.95Eu0.05AlO3. These peaks could be assigned to charge transfer (CT)transitions of Eu^3 -O^2- and Gd^3 -O^2- respectively. All the transitions observed in Gd0.95Eu0.05AlO3 are faithfully reproduced in the Y0.95Eu0.05AlO3, but with an exception of the ^8S7/2→^6I11/2 transition of Gd^3 . The 153 nm broad band could be the CT transition of Y^3 -O^2 - . Accordingly, the efficiency luminescence of (Gd, Y) BO3 : Eu^3 was explained as a result of CT transitions of Gd^3 -O^2- and Y^3 -O^2- under 147 nm excitation. Under VUV excitation, Gd0.95Eu0.05AlO3 exhibits a bright red luminescence with CIE chromaticity coordinates of (0.623, 0. 335) with a PL intensity of 30 of the commercial phosphor (Gd, Y) BO3 : Eu^3 (KX-504A). The PL spectrum of Y0.95Eu0.05AlO3 is similar to that of Gd0.95Eu0.05AlO3. Calculation of the color coordinates gives x = 0. 636, y = 0. 340 with a PL intensity of 50 of the (Gd, Y) BO3 : Eu^3 ( KX-504A) for Y0.95Eu0.05AlO3, and confirms that it has the appearance of pure spectral red, corresponding approximately to 608 nm. It can be concluded that LnAlO3:Eu^3 is a promising red VUV phosphor.     

Vacuum ultraviolet excited photoluminescence properties of Gd2O2CO3：Eu^3＋ phosphor

The Gd2O2CO3：Eu^3＋ with type-Ⅱ structure phosphor was successfully synthesized via flux method at 400 ℃ and their photoluminescence properties in vacuum ultraviolet （VUV） region were examined. The broad and strong excitation bands in the range of 153-205 nm owing to the CO3^2- host absorption and charge transfer （CT） of Gd^3＋-O2^- were observed for Gd2O2CO3：Eu^3＋. Under 172 nm excitation, Gd2O2CO3：Eu^3＋ exhibited strong red emission with good color purity, indicating Eu^3＋ ions located at low symmetry sites and the chromaticity coordination of luminescence for Gd2O2CO3：Eu^3＋ was （x=0.652, y=0.345）. The photoluminescence quenching concentration of Eu^3＋ excited by 172 nm for Gd2O2CO3：Eu^3＋ was about 5%. Gd2O2CO3：Eu^3＋ would be a potential VUV-excited red phosphor applied in mercury-free fluorescent lamps.     

Rare earth （Eu2＋,ce3＋） activated BaAIESi2O8 blue emitting phosphor

Blue emitting rare earth（Eu2＋,Ce3＋） doped BaAl2Si2O8 phosphors were synthesized by combustion methods at 600 oC. BaAl2Si2O8： Eu2＋ phosphor showed isolated broad blue emission band at 455 nm, when it was excited with the wavelength of 329 nm. Whereas BaAl2Si2O8：Ce3＋ phosphor exhibited blue emission band at 442 nm, under 303 nm excitation wavelength. These observed emission bands of Eu2＋ and Ce3＋ ions corresponded to 5d-4f allowed transitions. The position of emission band was calculated by using the equationE=Q[1-〔V/4〕^1/V）]× 10 （nEar/80）Also the spin orbit splitting difference in the ground state levels of Ce3＋ ion was studied by Gaussian curve fitting. Broad absorption and emission bands in blue regions made prepared phosphors a promising blue host for the white-LEDs.     

Photoluminescence of BaGdB9O（16）：Eu^3＋ co-doped Al^3＋ or Sc^3＋ under UV-VUV excitation

Single phase of BaGd0.9-xMxEu0.1B9O16 (M=Al or Sc, 0≤x≤0.3) powder was prepared by the solid-state reaction and its photoluminescence (PL) properties were investigated under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. Monitored with 613 nm emission, the excitation spectra of BaGd0.9-xMxEu0.1B9O16 consisted of three broad bands peaking at about 242, 208, and 142 nm, respectively. The one at about 242 nm originated from the charge transfer band (CTB) of O2-→Eu3+. The other two were assigned to the absorption of the host, which was overlapped with absorptions among borate groups, f→d transition of RE3+ (RE=Gd, Eu), and the charge transfer transition of O2-→Gd3+. The maximum emission peak was observed at about 613 nm in the emission spectra of BaGd0.9-xMxEu0.1B9O16 under both 254 and 147 nm excitation, which originated from the electric dipole 5D0→7F2 transition of Eu3+. When excited with 254 nm, the integral emission intensity of Eu3+ increased after Al3+ or Sc3+ substituting Gd3+ partly in BaGd0.9Eu0.1B9O16. Under 147 nm excitation, the integral emission intensity of Eu3+ decreased after some Gd3+ was replaced by Sc3+, but increased after adding appropriate Al3+ into BaGd0.9Eu0.1B9O16.     

Luminescent properties of MMgP_2O_7：Eu~（3＋）（M=Ca,Sr,Ba） phosphor

A series of red phosphors Eu3+-doped MMgP2O7(M=Ca,Sr,Ba) were synthesized by solid-state reaction method.X-ray powder diffraction(XRD) analysis confirmed the formation of pure CaMgP2O7,SrMgP2O7 and BaMgP2O7 phase.Photoluminescence spectra of MMgP2O7(M=Ca,Sr,Ba):Eu3+ phosphors showed a strong excitation peak at around 400 nm,which was coupled with the characteristic emission(350-400 nm) from UV light-emitting diode.The CaMgP2O7:Eu3+,SrMgP2O7:Eu3+ and BaMgP2O7:Eu3+ phosphors showed strong emission bands peaking at 612,593 and 587 nm,respectively.Due to the difference of the ion sizes between Ba2+(0.142 nm),Sr2+(0.126 nm),Ca2+(0.112 nm),Mg2+(0.072 nm) and Eu3+(0.107 nm),Eu3+ ions were expected to substitute for different sites in CaMgP2O7,SrMgP2O7 and BaMgP2O7 lattice.     

Luminescence properties of red phosphors Ca_（10）Li（PO_4）_7：Eu~（3＋）

A series of red phosphors Ca10Li (PO4)7:Eu3+ were synthesized by high temperature solid-state reaction method. Their luminescence properties were characterized by means of photoluminescence excitation and emission spectra,CIE chromaticity and quantum efficiency. Results indicated that the phosphors could be effectively excited by the near ultraviolet (NUV) light (393 nm). The main emission peaks of the phosphor were ascribed to the transition 5D0-7F2 (613 and 617 nm) of Eu3+ ion when samples were excited by...     

Combustion synthesis and luminescence properties of Ca4Y6（SiO4）60：Eu3＋ red phosphor for white LEDs

Eu3＋ activated Ca4Yt（SiO4）60 phosphors were prepared by combustion synthesis method, and their morphologies and lu- minescent properties were investigated. Field scanning electron microscopy （FSEM） confirmed that the crystallite sizes of nanoparti- cles with narrow diameter ranging from 30 to 60 rim. The excitation spectra of CaaY6（SiO4）60：Etl3＋ showed that there existed two strong excitation bands at around 399 nm （TFo----~SL6） and 469 nm （TF0---＊SD2）, which were consistent with the output wavelengths of near-UV and blue LEDs, respectively. The emission spectra of Ca4Y6（SiO4）60：Eu3＋ were dominant by a red peak located at 614 nm due to the 5Do→7TF2 transition of Eu3＋. With the increase of Eu3＋concentration, the luminescence intensity of the red phosphor reached maximum and then decreased. The optimum concentration for Eug＋in Ca4Y6（SiO4）60 was 21 mol.%.     

Tunable color emission in K3Gd（PO4）2:Tb3+,Sm3+ phosphor for n-UV white light emitting diodes

A series of K3Gd(PO4)2:Tb3+,Sm3+ phosphors were synthesized through solid state reaction. By co-doping Tb3+ and Sm3+into K3Gd(PO4)2 host and singly varying the doping concentration of Sm3+, tunable colors from green to yellow and then to orange were obtained in K3Gd(PO4)2:Tb3+,Sm3+ phosphors under the excitation at 373 nm. The energy transfer process from Tb3+ to Sm3+ was verified through luminescence spectra and fluorescence decay curves. Moreover, the energy transfer mechanism was demonstrated to be the quadrupole-quadrupole interaction. The results indicated that K3Gd(PO4)2:Tb3+,Sm3+ phosphors could be a potential application for n-UV white light emitting diodes.     

Photoluminescent properties of Ca2RE8（SiO4）6O2：A （RE=Y,Gd; A=Pb^2＋, Mn^2＋） phosphor films prepared by sol-gel process

Ca2RE8（SiO4）6O2：A （RE=Y, Gd; A=Pb^2＋, Mn^2＋） phosphor fdms were dip-coated on quartz glass substmtes through the sol-gel process. X-ray diffraction （XRD）, photoluminescence （PL） spectra as well as lifetimes were used to characterize the resulting films. Under short wavelength UV excitation, the film showed a red emission with medium intensity. The decay curve of Mn^2＋ luminescence in Ca2Gd8（SiO4）6O2：Pb Mn film could be fitted into a single exponential function. The lifetime of Mn^2＋ was 10.21 ms in Ca2Gd8（SiO4）6O2.     

A novel long lasting phosphor Sr5 （PO4）3FxCll_x：Eu2＋,Gd3＋ prepared in air condition

A series of blue long afterglow mixed halide-phosphate phosphors Sr5 （PO4）3 FxCll-x：Eu2＋,Gd3＋ were synthesized in air by traditional solid-state reaction routte. The crystal structures, photoluminescence, thermolurninescenee properties and afterglow proper- ties of the phosphors were characterized systematically using X-ray diffraction （XRD）, luminescence spectrophotometer, microcom- puter thermoluminescence dosimeter and single photon counter, respectively. Under 280 nm excitation, the broadband emissions of Eu2＋ ions were observed at 445 nm （blue） due to the 4f7→4f65d transition. It was demonstrated that there existed the self-reduction of the Eu3＋ to Eu2＋ ions in this special halide-phosphate matrix in air condition. The addition of Gd3＋ ions obviously enhanced the after- glow properties of the single doped Eu2＋ ions in the halide-phosphate phosphors. And the content of the fluoride anions also had sig- nificant influence on the afterglow properties. All results indicated that Srs （PO4）3 FxCI1-x：Eu2＋,Gd3＋ might be potential phosphors for long lasting phosphorescence （LLP） materials.     

Preparation and Long Persistence Red Luminescence of M0.2Ca0.8TiO3 ： Pr^3＋ （M = Mg^2＋ , Sr^2＋ , Ba^2＋ , Zn^2＋）

M0.2Ca0.8TiO3 : Pr^3 (M = Mg^2 , Sr^2 , Ba^2 , Zn^2 ) long persistence red phosphors were prepared by solid state reaction. The influence of the partially replacing Ca^2 in CaTiO3 with Mg^2 , Sr^2 , Ba^2 , Zn^2 on the excitation spectra, the emission spectra and the long persistence properties were studied. The results suggest that certain quantity of Mg^2 , Sr^2 , Ba^2 , Zn^2 which partially replace Ca^2 can enhance the luminescent intensity and prolong the afterglow persistence of the samples. The intensity of Mg0.2Ca0.8TiO3: Pr^3 is above all of the samples. Take Mg0.2Ca0.8TiO3:Pr^3 as the basic sample, the influence of Pr^3 concentrations (C (Pr^3 )) on the long afterglow properties were also studied.The results suggest that when the C (Pr^3 ) is 0.10% (tool fraction) the intensity of the sample is the highest. The excitation spectra of all these samples show broad band spectra ranging from 300 - 500 nm peaking at about 342 nm. The emission spectra also exhibit a broad band peaking at 613 nm (CaTiO3: Pr^3 is 612 nm). XRD research indicates that the crystalline phases change due to the replacement of divalent metal ions. The research on the thermoluminescence spectra of Mg0.2Ca0.8TiO3:Pr^3 indicates that the peak is at 107.35℃ and the depth of the trap energy is about 0.852 eV.     

VUV Spectroscopy of GdPO4： Eu^3＋ and GdBO3： Eu^3＋

The emission and the excitation spectra of GdPO4 ： Eu^3＋ and GdBO3： Eu^3 ＋ prepared by solid state reaction method were investigated using the synchrotron radiation source of SUPERLUMI station of HASYLAB. The energy transfer between Gd^3＋ and Eu^3＋ was discussed with the probability of quantum cutting process. In the excitation spectra monitoring the red emission from Eu^3＋ , the distinct lines corresponding to the intraconfigurational 4f-4f transitions from Gd^3＋ were observed for both samples, indicating an efficient energy transfer from host Gd^3＋ ions to the doped Eu^3＋ ions. The efficient energy transfer is necessary for the quantum cutting process based on the two-step energy transfer from Gd^3＋ to Eu^3＋ . However, the overlapping of the lines corresponding to Gd^3＋ ：^8S7/2→^6GJ and the broad excitation band （180 - 270 nm） due to Eu^3＋- O^2- charge transfer states （CTS） around 200 nm cause excitation energy on ^6GJ levels to dissipate into CTS by direct energy transfer, unfavorable to the cross relaxation energy transfer between Gd^3＋ and Eu^3＋, thus unfavorable to the quantum cutting process. With the help of the general rules governing the energy positions of Eu^3＋-O^2- ：CTS, the suggestions concerning searching suitable oxide hosts for Gd^3＋-Eu^3＋ quantum cutting were made.