Fabrication of YAG:Ce^(3+) and YAG:Ce^(3+),Sc^(3+) Phosphors by Spark Plasma Sintering Technique

In this study,a single-doped phosphors yttrium aluminum garnet(Y_(3)Al_(5)O_(12),YAG):Ce^(3+),single-doped YAG:Sc^(3+),and double-doped phosphors YAG:Ce^(3+),Sc^(3+) were prepared by spark plasma sintering(SPS)(lower than 1 200℃).The characteristics of synthesized phosphors were determined using scanning electron microscopy(SEM),X-ray diffraction(XRD),and fluorescence spectroscopy.During SPS,the lattice structure of YAG was maintained by the added Ce^(3+) and Sc^(3+).The emission wavelength of YAG:Ce^(3+) prepared from SPS(425-700 nm) was wider compared to that of YAG:Ce^(3+) prepared from high-temperature solid-state reaction(HSSR)(500-700 nm).The incorporation of low-dose Sc^(3+) in YAG:Ce^(3+) moved the emission peak towards the short wavelength.

Mn^(4+) activated phosphors in photoelectric and energy conversion devices

Owing to their high luminous efficiency and tunable emission in both red light and far-red light regions,Mn^(4+)ion-activated phosphors have appealed significant interest in photoelectric and energy conversion devices such as white light emitting diode(W-LED),plant cultivation LED,and temperature thermometer.Up to now,Mn^(4+)has been widely introduced into the lattices of various inorganic hosts for brightly redemitting phosphors.However,how to correlate the structure-activity relationship between host framework,luminescence property,and photoelectric device is urgently demanded.In this review,we thoroughly summarize the recent advances of Mn^(4+)doped phosphors.Meanwhile,several strategies like co-doping and defect passivation for improving Mn^(4+)emission are also discussed.Most importantly,the relationship between the protocols for tailoring the structures of Mn^(4+)doped phosphors,increased luminescence performance,and the targeted devices with efficient photoelectric and energy conversion efficiency is deeply correlated.Finally,the challenges and perspectives of Mn^(4+)doped phosphors for practical applications are anticipated.We cordially anticipate that this review can deliver a deep comprehension of not only Mn^(4+)luminescence mechanism but also the crystal structure tailoring strategy of phosphors,so as to spur innovative thoughts in designing advanced phosphors and deepening the applications.

Investigations on Valence-Change Behaviors of Europium Ions in Eu-Doped Aluminate and Silicate Phosphors

Compounds of Sr3Al2O6 ： Eu, SrgAl14O25 ： Eu, and BaZnSiO4 ： Eu were synthesized by high-temperature solid state reactions. The doping Eu^3 ＋ ions were partially reduced to Eu^2＋ in Sr4Al14O25：Eu and BaZnSiOg：Eu prepared in an oxidizing atmosphere, N^2 ＋ O2. However, such an abnormal reduction process could not be performed in Sr3Al2O6：Eu, which was also prepared in an atmosphere of N^2 ＋ O2. Moreover, even though Sr3A1EO6：Eu was synthesized in a reducing condition CO, only part of the Eu^3 ＋ ions was reduced to Eu^2 ＋ . The existence of trivalent and divalent europium ions was confirmed by photoluminescent spectra. The different valence-change behaviors of europium ions in the hosts were attributed to the difference in host crystal structures. The higher the crystal structure stiffness, the easier the reduction process from Eu^3 ＋ to Eu^2 ＋ .

Effect of fluxes on structure and luminescence properties of Y_3Al_5O_(12):Ce^(3+) phosphors

Ce3＋-activated yttrium aluminum garnet （YAG） was prepared by the solid-state reaction, in which H3BO3, LiF, NaF, KF and BaF2 were used as the fluxes. The effect of fluxes on optical properties of phosphors was studied in detail, especially the fluxes of alkali fluorides, which could enhance the emission intensity and change the wavelength of emission peaks. Among these YAG：Ce phosphors, the phosphor sintered with H3BO3 and NaF exhibited the strongest emission. The emission peaks of phosphors prepared with fluxes from LiF to KF were shifted to long wavelength. The effect of NaF concentration on the emission intensity of YAG：Ce was also investigated. The value of emission intensity reached the maximum when the concentration of NaF was 0.5%.

Preparation and luminescent properties of CaAl_2O_4:Eu^(3+),R^+(R=Li,Na,K) phosphors

CaAl2O4:Eu3+,R+(R=Li+,Na+,K+) red phosphors were synthesized by solid state reaction method.X-ray diffraction(XRD) and photoluminescence(PL) were employed to characterize their structural and luminescent properties.It was found that the optimal sintering temperature and sintering time were 1200 °C and 4 h,respectively.The optimal concentration of doped Eu3+ was 3 mol.%.Furthermore,under ultraviolet excitation with a wavelength of 254 nm,these samples showed red luminescence which were probably attributed to...

Synthesis and Characterization of Cerium-Doped Lutetium Aluminum Garnet Phosphors by Nitrate-citrate Sol-Gel Combustion Process

Nanosized cerium-doped lutetium aluminum garnet （LuAG：Ce） phosphors were prepared by nitrate-citrate solgel combustion process using 1：1 ratio of the citrate：nitrate. The prepared LuAG：Ce phosphors were characterized by XRD, TEM, photoluminescence and radioluminescence spectra excited by UV and X-ray, respectively. The purified crystalline phase of LuAG：Ce was obtained at 900 ℃ by directly crystallizing from amorphous materials. The resultant Lu- AG：Ce phosphors were uniform and had good dispersivity with an average particle size of about 30 urn. Both photoluminescence and radioluminescence were well-known Ce^3＋ emissions located in the range of 470 -600 nm consisting of two emission bands because of the transition from the lowest 5d excited state （2D） to the 4f ground state of Ce^3＋, which matched well with the sensitivity curve of the Si-photodiode. There was a little red shift for the emission components from the UV-excited emission spectrum to the X-ray-excited emission spectrum. The fast scintillation decay component of 26 ns satisfies the requirements of fast scintillators.

Sol-gel processed Ce^(3+), Tb^(3+) codoped white emitting phosphors in Sr_2Al_2SiO_7

Sr2Al2SiO7：Ce^3＋, Tb^3＋ white emitting phosphors were fabricated using the sol-gel method. X-Ray Powder Diffraction （XRD） analysis confirmed the formation of Sr2Al2SiO7：Ce^3＋, Tb^3＋. Scanning Electron Microscopy （SEM） observation indicated that the microstructure of the phosphor consisted of regular fine grains with an average size of about 0.5-1 μm. Luminescence properties were analyzed by measuring the photoluminescence spectra. The Ce^3＋, Tb^3＋-codoped Sr2Al2SiO7 phosphors showed four main emission peaks： one at 414 nm for Ce^3＋ and three at 482, 543, and 588 nm for Tb^3＋. The emission spectra of the samples with different doping concentrations showed that the Tb^3＋ emission was dominant because of the persistent energy transfer from Ce^3＋. The decay characteristic was better than that prepared by the solid-state process in the comparable condition. The codoped phosphor displayed long persistent white phosphorescence.

Microwave Assisted Sintering and Photoluminescence Properties of BaaSi6OleNe：Eu^2＋ Green Phosphors

Eu^2＋-doped Ba3Si6012N2 green phosphors were prepared by microwave assisted sintering method at 1275℃ for 4 h, while the counterparts using conventional solid-state reaction method were synthesized at temperature higher than 1300℃ and for to 10 h. Microwave assisted sintering could reduce the activation energy and enhance the diffu- sion rate, thus greatly improved the sintering. Moreover, the influence of Si3N4 content on phase formation, morphol- ogy, absorption, and quantum efficiency, and photoluminescence properties of phosphors were studied. As a result, the Ba3Si6OI2N2：Eu^2＋ samples sintered by microwave assisted sintering method have a higher phase purity and photo- luminescence intensity under ultraviolet excitation as compared with samples sintered in the conventional tube furnace The proposed method is a potential preparation method for the oxynitride phosphors with strong photoluminescence and high phase purity.

Synthesis and luminescence properties of Ca_2SiO_4-based red phosphors with Sm^(3+) doping for white LEDs

Sm3＋-activated Ca2SiO4 red phosphors were prepared by the conventional high-temperature solid-state reaction method, and the effects of sodium （Na＋） and samarium （Sm3＋） ions doping concentrations on their crystal structure and luminescent properties were investigated by X-ray diffraction （XRD） and fluorescent spectrofluorometer. XRD patterns demonstrate that a well-crystalline structure forms in the phosphors when they are treated by calcination at 1200~C for 4 h, and the excitation spectra exhibit good absorption in the range between 350 and 420 nm. Under the irradiation of 405 nm near-ultraviolet （NUV） light, the spectra of the phosphors show a main emission peak at 601 nm attributed to the 4G5/2→6H7/2 transition of Sm3＋ ions, and its intensity is greatly influenced by the concentrations of Sm3＋ and Na2CO3. When the concentrations of Sm3＋ ions and Na2CO3 are 2mol% and 6mol%, respectively, the optimal emission intensity can be obtained. From strong absorption in the near ultraviolet zone, the Na0.06Sm0.02Ca1.92SiO4 phosphor is a promising red-emitting phosphor for white light emitting diodes （W-LEDs）.

Synthesis and Luminescent Properties of Superfine Sr_2CeO_4 Phosphors by Sol-Gel Auto-Combustion Method

Citric acid complexing sol-gel auto-combustion method was explored to synthesize superfine Sr2CeO4 phosphors using the inorganic salts Sr（NO3）2 and Ce（NO3）3 as raw materials together with citric acid （CA） as a chelating agent. TGDTA, XRD, SEM and photoluminescence spectra were used to investigate the formation process, microstructure and luminescent properties of the synthesized Sr2CeO4. The results show that the crystallization of Sr2CeO4 begins at about 800 ℃ and completes around 900 ℃ with an orthorhombic structure. When the calcination temperature is above 1000 ℃, Sr2CeO4 partly decomposes into SrCeO3. SEM studies show that the particles of Sr2CeO4 obtained at 900 ℃ are sphericallike shape and superfine with diameter below 100 nm. The excitation spectrum of the superfine Sr2CeO4 phosphors displays a broad band with two peaks around 290 and 350 nm respectively. The former peak is stronger than the latter one. This broad band is due to the charge transfer （CT） band of the Ce^4＋ ion. Excited by a radiation of 290 nm, the superfine phosphors emit a strong blue-white fluorescence, and the emission spectrum shows a broad band with a peak around 470 nm, which can be assigned to the f→t1g transition of Ce^4＋ . It is found that the emission intensity is affected by the calcination temperature.

Synthesis of SrAl_2O_4:Eu^(2+),Dy^(3+) phosphors by the coupling route of microemulsion with coprecipitation method

Nano-sized SrAl2O4：Eu^2＋,Dy^3＋ phosphors with good monodispersity and narrow size distribution were synthesized by the coupling of water-in-oil （W/O） microemulsion with coprecipitation method. The phase composition, morphology, crystallinity, excitation spectra, emission spectra, and afterglow decay of SrAl2O4：Eu^2＋,Dy^3＋ nanophosphors were measured. It was found that the amount of surfactant that was used had an important effect on the shape and average size of the phosphor particles. SrAl204 phase of the phosphors showed an increase with the increase in calcination temperature. When the calcination temperature reached 1150℃, the fine crystal of SrAl2O4 was formed and the long afterglow luminescence could be obviously observed. In comparison with the samples prepared by the high-temperature solid-state method, the calcination temperature showed an obvious decrease and a dear blue shift occurred in the excitation and emission spectra of the sample. The afterglow time could be more than 8 h.

Luminescence properties of YAl_3(BO_3)_4 phosphors doped with Eu^(3+) ions

YAl3 （BO3）4： Eu^3＋ phosphors were prepared by the conventional solid state reaction. The phase structure and morphology were investigated by X-ray diffraction （XRD） and scanning electron microscope （SEM）. Doping YAl3（BO3）4： Eu^3＋ phosphors with concentration of Eu^3＋ ions of 0, 2, 5, 8 and 10 mol% were studied and their luminescent properties at room temperature were discussed. The excitation spectrum of Y0.95Eu0.05Al3（BO3）4 was composed of a broad band centered at about 252 nm and a group of lines in the longer wavelength region. In the emission spectra, the peak wavelength was about 614 nm under a 252 nm UV excitation. The optimal doping concentration of Eu^3＋ ions in YAl3（BO3）4： Eu^3＋ phosphors was 8 mol%.

Synthesis and characterization of Sr_3Al_2O_6:Eu^(2+), Dy^(3+) phosphors prepared by sol-gel-combustion processing

A type of red luminescent Sr3Al2O6：Eu2＋, Dy3＋ phosphor powder is synthesised by sol-gel-combustion processing, with metal nitrates used as the source of metal ions and citric acid as a chelating agent of metal ions. By tracing the formation process of the sol-gel, it is found that it is necessary to reduce the amount of NO3 by dropping ethanol into the solution for forming a stable and homogeneous sol-gel. Thermogravimetric and Differential Scanning Calorimeter Analysis, x-ray diffractionmeter, scanning electron microscopy and photoluminescence spectroscopy are used to investigate the luminescent properties of the as-synthesised Sr3A1206：Eu2＋, Dy3＋. The results reveal that the Sr3Al2O6 crystallises completely when the combustion ash is sintered at 1250℃. The excitation and the emission spectra indicate that the excitation broadband lies mainly in a visible range and the phosphors emit a strong light at 618 nm under the excitation of 472 nm. The afterglow of （Sr0.94Eu0.03Dy0.03）3Al2O6 phosphors sintered at 1250℃ lasts for over 1000 s when the excited source is cut off.

Up-conversion Properties of Er^(3+)/Yb^(3+) Co-doped Li_3Ba_2Gd_3(MoO_4)_8 Phosphors

Er3＋/Yb3＋ co-doped Li3Ba2Gd3（MoO4）8 phosphors were synthesized by conven- tional solid state reaction method, and their structure and spectral properties were investigated. The diffuse reflectance spectra showed that the 4I15/2→4I11/2 transition of Er3＋ and the 2F7/2→2F5/2 transition of Yb3＋ ions were highly overlapped. Under the excitation of 980 nm, three up-conver- sion （UC） luminescence bands around 530, 555 and 660 nm were observed, corresponding to the 2H11/2→ 4I15/2, 4S3/2 → 4I15/2 and 4F9/2-→4I15/2 transitions of Er3＋ ions, respectively. The effects of the concentration and pumping power on the UC intensities of Li3Ba2Gd3（MoO4）8：Er3＋/yb3＋ phosphors were investigated, and the possible UC mechanism was proposed based on the results.

Sol-Gel Preparation and Luminescence Properties of BaMgAl_(10)O_(17):Eu^(2+) Phosphors

The synthesis of BaMgAl10O17： Eu^2＋ （BAM） phosphors using the sol-gel method and their luminescence properties were reported. The blue-light emitting BAM was synthesized using citric acid and ethylene glycol as chelating materials. Emission of blue-light was obtained from these phosphors. The luminescent intensity increases as the temperature of heat treatment is increased, This study investigated the effects of the molar ratio of ethylene glycol to citric acid （Ф value）, with respect to the phase formation and luminescence properties of BAM. The variation of the Фvalue resulted in the change of the sol-gel reaction mechanism and the microstructures of the resultant powders. An increase in Фvalue leads to an increase in the rate of BAM phase formation. The photoluminescent intensity of the prepared phosphors increases with heating temperatures because of enhanced crystallization.

Long-Lasting Properties of Rare Earth-Doped Y_2O_2S Phosphors

The aim of this presentation is to report a new result of afterglow materials. The Y 2O 2S∶Ln 3+ (Ln=Sm, Tm) phosphors show bright reddish orange and orange-yellow colors when excited by UV or visible light. The main spectroscopic characterizations of Sm 3+ and Tm 3+ in yttrium oxysulfide and their long-lasting phosphorescence were measured and discussed in this presentation. Their long-lasting phosphorescence can be seen by the naked eyes clearly for about one hour in the dark room after the irradiation light sources were removed. XRD and photoluminescence (PL) spectra as well as the luminance decay were used to characterize these long-lasting phosphorescence phosphors. The results of XRD indicate that the products synthesized through the flux fusion method under 1050 ℃ for 6 h have a good crystallization without any detectable amount of impurity phase. Both the PL spectra and luminance decay results reveal that these phosphors have efficient luminescent and good long-lasting properties. We believe that the experimental data gathered in our present work will be useful in finding some new long-lasting phosphors with different colors.

Effects of RE^(3+)(RE=La,Ce,Pr,Sm,Dy,Ho,Er,and Tm) on the luminescence of Sr_2MgSiO_5:Eu^(2+) phosphors

Sr2MgSiO5：Eu^2＋phosphors were synthesized through a high temperature solid state reaction method.The phase and luminescence properties of the samples were characterized by X-ray diffraction（XRD） and a luminescence spectrometer.The effects of RE^3＋（RE = La,Ce,Pr,Sm,Dy,Ho,Er,and Tm） on the luminescent properties of the samples were studied.The results show that the luminescence spectrum of Sr2MgSiO5：Eu^2＋ is a broad band composed of two emission peaks,at 460 and at 530 nm under near-ultraviolet excitation.Rare earth ions Re^3＋（RE = La,Ce,Pr,Sm,Dy,Ho,Er,and Tm） have great influence on the emission of Sr2MgSiO5：Eu^2＋ phosphors.The La^3＋ ion in Sr2MgSiO5：Eu^2＋ phosphors greatly enhances the emission at 460 and 530 nm.

A novel Dy^(3+)-doped GdPO_4 white-light phosphors under vacuum ultraviolet excitation for Hg-free lamps application

Novel Dy3＋-doped GdPO4 white light phosphors with monoclinic system were successfully synthesised by hydrothermal method at 240℃. This paper investigates the luminescence properties of white-light Gd1-xPO4 ： xDy3＋ under vacuum ultraviolet （VUV） excitation. The strong absorption at around 147 nm in excitation spectrum energy can be transferred to the energy levels of Dy3＋ ion from the host absorption. Additionally, this white light phosphors are activated by a single Dy3＋ ion and with a lower preparation temperature, which tend to decrease the consumption of rare earth resource and energy. Therefore, the luminescence of Gd1-xPO4 ： xDy3＋ under VUV excitation is effective, and proves to be promising in application to mercury-flee lamp.

Synthesis and Luminescence Properties of(Y, Gd)(P, V)O_4:Eu^(3+), Bi^(3+) Red Nano-phosphors with Enhanced Photoluminescence by Bi^(3+), Gd^(3+) Doping

A series of(Y_(1-y), Gdy)_(0.95-x)(P_y, V_(1-y))O_4 :0.05Eu^(3+), xBi^(3+)+phosphors have been successfully prepared by a subsection method. The crystal structure, surface morphology and luminescence properties were investigated. It was found that the sintered samples crystallized in a tetragonal crystal system with space group I_(41)/amd(a = b = 0.7119 nm, c = 0.6290 nm). The products presented rod-like morphology with length of 100-150 nm and width of 50-100 nm. A maximum peak at 619 nm(~5D_0 →~7F_2) was observed in emission spectrum of the phosphors. It was also found that co-doping of Bi^(3+)+, P5+and Gd^(3+)ions into YVO_4:Eu^(3+)can not only made the right edge of the excitation band shift to the long-wavelength region, but also increased the emission intensity at 619 nm sharply and decreased the lifetime of fluorescence decay. These results may expand the application scope of the phosphors.

Novel Dy^(3+)-doped Gd(PO_3)_3 white-light phosphors under VUV excitation for Hg-free lamps application

Novel Dy^3＋-doped Gd（PO3）3 white light phosphors each with an orthorhombic system are successfully synthesized by solid-state reaction.The luminescence properties of white-light Gd1-x（PO3）3：xDy^3＋（0 〈 x ≤ 0.25） under vacuum ultraviolet（VUV） excitation are investigated.The strong absorption at around 147 nm in excitation spectrum energy can be transferred to the energy levels of Dy^3＋ ion from the host absorption.Additionally,the white light phosphor is activated by a single Dy^3＋ ion.Therefore,the luminescence of Gd1-x（PO3）3：xDy（0 〈 x ≤ 0.25） under VUV excitation is effective,and it has the promise of being applied to mercury-free lamps.