A new green-yellowish emitting fluoro-apatite compound phosphor Ba_3TbK(PO_4)_3F:Sm~(3+) with high thermal stability

A novel fluoro-apatite-type compound, Ba_3TbK(PO_4)_3F was developed via a high-temperature solid-state reaction route for the first time. X-ray photoelectron spectroscopy(XPS), scanning electron microscopy(SEM), and high-resolution TEM(HRTEM) were used to investigate the component element and microstructure of the phosphor was systematically investigated. The luminescence properties of Ba_3TbK(PO_4)_3F:Sm~(3+) were investigated systemically. The results revealed that the Ba_3TbK(PO_4)_3F:Sm~(3+) phosphor could be efficiently excited in a broad wavelength region ranging from 200 to 400 nm, which matched perfectly with the ultraviolet(UV) light-emitting diode(LED) chips. Based on the energy transfer(ET) between Tb~(3+) and Sm~(3+), the color hue of Ba_3Tb_1–nK(PO_4)_3F:n Sm~(3+)(n=0–0.03) was modulated from green(0.305, 0.591) to yellow(0.486, 0.437) area by controlling the Sm~(3+)doping concentration. The critical distance between Tb~(3+) and Sm~(3+) ions in Ba_3TbK(PO_4)_3F:Sm~(3+) was calculated and the corresponding energy quenching mechanism was identified. Fascinatingly, both the Ba_3TbK(PO_4)_3F and Ba_3Tb_(0.995)K(PO_4)_3F: 0.005Sm~(3+) phosphors exhibited very high thermal stability from room temperature(25 oC) to 300 oC, which is extremely important for practical application. In addition, the activation energy for thermal quenching of the Ba_3Tb_(0.995)K(PO_4)_3F:0.005Sm~(3+) sample was estimated to be as high as 0.312 eV. These findings demonstrated that as-prepared phosphor may serve as a high-performance candidate for the application in w-LEDs.     

Samarium doped apatite-type orange-red emitting phosphor Ca_5(PO_4)_2SiO_4 with satisfactory thermal properties for n-UV w-LEDs

A novel single-phase Sm~(3+) activated Ca_5(PO_4)_2SiO_4 phosphor was successfully fabricated via a conventional solid-state method, which can be e fficie ntly excited by near ultraviolet(n-UV) light-emitting chips.The crystal structure and luminescence properties were characterized and analyzed systematically by using relevant instruments. The Ca_5(PO_4)_2SiO_4:Sm~(3+) phosphor shows an orange-red emission peaking at600 nm under the excitation of 403 nm and the optimal doping concentration of Sm~(3+) is determined to be 0.08, The critical distance of Ca_5(PO_4)_2SiO_4:0.08 Sm~(3+) is calculated to be 1.849 nm and concentration quenching mechanism of the Sm~(3+) in Ca_5(PO_4)_2SiO_4 host is ascribed to energy transfer between nearestneighbor activators. The decay time of Ca_5(PO_4)_2 SiO_4: 0,08 Sm~(3+) is determined to be 1.1957 ms. In addition, the effect of temperature on the emission intensity was also studied, 72.4% of the initial intensity is still preserved at 250 ℃, better thermal stability compared to commercial phosphor YAG:Ce~(3+) indicates that Ca_5(PO_4)_2SiO_4:0.08 Sm3+ has excellent thermal stability and active energy is deduced to be 0.130 eV.All the results demonstrate that orange-red emitting Ca_5(PO_4)_2SiO_4:0.08 Sm~(3+) phosphor exhibits good luminescent properties. Owing to the excellent thermal quenching luminescence property,Ca_5(PO4)_2SiO_4:0.08 Sm~(3+) phosphor can be applied in n-UV white light emitting diodes and serve as the warm part of white light.     

Photoluminescence properties of a novel orange-red emitting Ba_2CaZn_2Si_6O_(17):Sm~(3+) phosphor

Novel orange-red emitting Ba_2Ca_(1–x)Zn_2Si_6O_(17):x Sm~(3+)(0.02≤x≤0.08) phosphors were synthesized using conventional solid-state reaction method under air atmosphere. The phase formation of the samples was characterized by powder X-ray diffraction patterns. Scanning electron microscopy(SEM) and photoluminescence properties were also investigated. The narrow excitation and emission spectra indicated the typical 4f-4f transitions of Sm~(3+). The dominant excitation line was around 405 nm attributed to ~6H_(5/2)→ ~4F_(7/2) and the emission spectrum consisted of four emission peaks at 562, 600, 647, and 708 nm corresponding to the various transitions ~4G_(5/2) to ~6HJ(J=5/2, 7/2, 9/2 and 11/2) of the Sm~(3+) ions in the same order. The strongest emission band located at 600 nm was attributed to ~4G_(5/2)→~6H_(7/2) transition of Sm~(3+), producing bright orange-red color emission. The optimal dopant concentration of Sm3+ ion in Ba_2CaZn_2Si_6O_(17):x Sm~(3+) phosphor was around 4 mol.% and the critical transfer distance(Rc) of Sm~(3+) was calculated to be 2.65 nm. Decay time varied with the Sm~(3+) concentrations in Ba_2 CaZn_2Si_6O_(17) phosphors. In addition, the Commission International del'Eclairagethe(CIE) chromaticity coordinates of Ba_2Ca_(0.96)Zn_2Si_6O_(17):0.04Sm~(3+) phosphor was located in the orange-red region(0.547, 0.450) and the correlated color temperature(CCT) was 2543 K. The present results indicated that Sm~(3+) activated Ba_2CaZn_2Si_6O_(17) phosphors may be used as an orange-red emitting phosphor for near-ultraviolet(n-UV) based white light emitting diodes(WLEDs) applications.     

Influence of reaction parameters on the luminescence properties of monodisperse NaGd(1−x−y)(WO4)2:xEu3+,yTb3+ phosphor by molten salt synthesis

Eu~(3+) activated and Eu~(3+), Tb~(3+) co-activated monodisperse sodium double tungstates NaGd(WO4)2 phosphors were prepared by molten salt method at 750 ℃ for 10 h using NaCl as a flux. The crystal structure and morphology of the as-synthesized phosphors were measured by XRD and SEM, respectively. The photoluminescence properties were characterized by PL spectra, decay lifetime and CIE. The presence of NaCl plays an important role in the morphology and luminescence properties. In this work,NaCl and one of the raw material Na_2 CO_3 in a certain proportion will form a low eutectic salt to decrease the reaction temperature and benefit the formation of monodisperse NaGd(WO_4)_2 crystals. The color of Eu~(3+) and Tb~(3+) co-doped NaGd(WO_4)_2 phosphors can be tuned from creamy white to orange, red and green by adjusting the doping concentration of rare earth ions, since the emission contain the broad blue-green emission origin from NaGd(WO_4)_2 host and characteristic red and green emission origin from Eu~(3+) and Tb~(3+) ions. The electroluminescent spectra and CIE measurement shows that the LED device with NaGd_((1-x))(WO_4)_2:xEu~(3+)(x = 0.24) phosphor can be excited by 365 nm and 380 nm LED chip, and their CIE coordinate is(x = 0.45, y = 0.45) and(x = 0.36, y = 0.37), Ra is 80.3 and 86.3, T_c is 3196 and4556 K, respectively. As a single-component phosphor, NaGd(WO_4)_2:Eu~(3+),Tb~(3+) have potential application in UV-pumped WLEDs.     

Synthesis and luminescent properties of Ba_2V_2O_7:Sm~(3+)

Samarium doped pyrovanadate Ba_2V_2O_7:Sm~(3+) phosphors were synthesized by traditional high-temperature solid-state reaction method. The phase and the structure of the samples were characterized by powder X-ray diffraction(XRD), and the luminescent properties and the energy transfer mechanism of the material were investigated using quantitative photoluminescence(PL) spectroscopy. The excitation spectrum of the sample exhibited a broad ultraviolet(UV) band with maximum at around 341 nm due to V–O charge transfer transition of the host. The emission spectrum displayed a yellow-greenish broadband(peaking at around 498 nm) coming from the host Ba_2V_2O_7 and three narrow peaks(at 561, 599 and 646 nm) attributed to the dopant Sm~(3+) ions. The PL spectra revealed the energy transfer from the host to the Sm~(3+) ions. In addition, the color coordinates and the color temperature of the phosphor Ba_(1.95)V_2O_7:5%Sm~(3+) were(0.314, 0.365) and 6135 K, respectively, under 365 nm excitation, suggesting it to be a candidate of single-phase converting phosphors for white-light-emitting diodes(WLEDs) with near-UV chips.     

A novel blue-purple Ce~(3+) doped whitlockite phosphor:Synthesis,crystal structure,and photoluminescence properties

At present,the rare earth(RE) ions doped phosphors have attracted more and more attention because of their excellent properties.In this paper,a series of novel blue-purple β-Ca_3(PO_4)_2:Ce~(3+) phosphors were synthesized by a high temperature solid phase method.The X-ray diffraction(XRD),infrared spectrum,energy dispersive spectroscopy(EDS),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),photoluminescence excitation and emission spectra were used to investigate the crystal structure,composition and the luminescent properties of the resulting samples.The phosphor shows a strong absorption in the ultraviolet band.Under the excitation of 269 nm,the phosphor emits a strong purple fluorescence ranging from 360 to 520 nm.When Ce~(3+) doping content is 0.07 mol,the strongest luminescence intensity is reached,and the concentration quenching mechanism is dipole-dipole(d-d)interaction for Ce~(3+) based on Dexter theory.     

Luminescence properties of near-UV excitable yellow-orange light emitting warm CaSrAl2SiO7:Sm3+ phosphors

Single-phase CaSrAl_2 SiO_7:Sm~(3+) phosphors were synthesized by traditional high temperature solid state reaction method. Formation of samples and phase analysis were confirmed by X-ray diffraction technique. Morphology was done by field emission scanning electron microscopy and elemental compositions were confirmed by energy dispersive X-ray analysis. Present phosphors have tetragonal crystallography with space group P42_1 m. Average crystallite size was calculated by using Scherrer and Williamson-Hall method. Photoluminescence study of CaSrAl_2 SiO_7:Sm~(3+) phosphor was investigated.Under different excitation wavelengths, PL spectra consist of four emission bands at 564, 570, 601 and650 nm. The emission bands located at 564 and 570 nm are associated with the transition ~4 G_(5/2)→~6 H_(5/2)while emission bands at 601 and 650 nm are due to ~4 G_(5/2)→~6 H_(7/2) and ~4 G_(5/2)→~6 H_(9/2),respectively.Intense emission was obtained when phosphor was excited under 404 nm wavelength. Non-radiative energy transfer process involved in concentration quenching, was also discussed. CIE coordinate is found in yellow-orange region, hence CaSrAl_2SiO_7:Sm~(3+) phosphors emit yellow-orange light when efficiently excited by near UV(～400 nm) LED chip. Color purity and CCT of the phosphor were determined; CCT suggests that present phosphor is a good candidate as a warm yellow-orange color emitting phosphor. Effect of different heating rates and different UV exposure time on the TL glow curve of the phosphor was investigated. Activation energies and kinetic parameters for different traps were calculated by using peak shape method. TL emission spectrum was also recorded. Present article explains all the possible mechanisms associated with luminescence process in CaSrAl_2 SiO_7:Sm~(3+) phosphors.     

Effect of Eu~(3+) contents on structure and luminescence properties of Na_3Bi_(2–x)(PO_4)_3:xEu~(3+) and Na_3Bi_(1–x)(PO_4)_2:xEu~(3+) phosphors

A series of Na_3Bi_(2–x)(PO_4)_3:xEu~(3+) and Na_3Bi_(1–x)(PO_4)_2:xEu~(3+) phosphors were successfully synthesized by solid-state method.The structure and luminescence properties were carefully investigated.The excitation spectra presented an obvious excitation band,and the peak was located at 396 nm,which matched well with the popular emissions from near-UV light-emitting diode chips.With the phase of Na_3Bi_(2–x)(PO_4)_3:xEu~(3+) changing to that of Na_3Bi_(1–x)(PO_4)_2:xEu~(3+),the intensity of magnetic dipole transition(~5D_0→F_1) at 598 nm became stronger than that of electric dipole transition(~5D_0→~7F_2) at 621 nm.Under 396 nm excitation,the chromaticity coordinates and the decay curves of the entitled phosphors were also investigated.Based on all experiments without concentration quenching,we could control the luminescence intensity of the material by adjusting the doping amount of the active ions.All results indicated that Na_3Bi_(2–x)(PO_4)_3:xEu~(3+) and Na_3Bi_(1–x)(PO_4)_2:xEu~(3+) phosphors have potential application as red phosphors in near UV chip-based white light emitting diodes.     

Photoluminescence properties and energy transfer of a single-phased white-emitting NaAlSiO_4:Ce~(3+),Sm~(3+) phosphor

A series of tunable phosphors NaAlSiO_4:Ce~(3+),Sm~(3+) were synthesized using a conventional high-temperature, solid-state method. Crystal structure, photoluminescence excitation, and emission spectra with fluorescence decay curves were investigated. Under UV excitation(325 nm), NaAlSiO_4:Ce~(3+),Sm~(3+) showed strong blue emission located at 444 nm and orange-reddish emission centered at 563, 601, 648 and 712 nm, stemming from the characteristic emission for 4f-5d transition of Ce~(3+) and ~4G_(5/2)→~6H_J(J=5/2, 7/2, 9/2, 11/2) transition of Sm~(3+), respectively. In addition, we studied the detailed energy transfer process between Ce~(3+) and Sm~(3+) and found that it belonged to dipole-dipole resonance energy transfer. Furthermore, we noted that the white light emitting from the Ce~(3+), Sm~(3+) co-doped phosphors with the color coordinate(x=0.313, y=0.283) could be observed under 325 nm excitation, which was close to the ideal white light(x=0.33, y=0.33). The results indicated that this phosphor has a potential application as a single-phased alumino-silicate phosphor for ultraviolet white light-emitting diodes(UV-WLEDs).     

A novel narrow band UV-B emitting phosphor-YPO_4:Sb~(3+),Gd~3

YPO_4 phosphors single-doped with Sb~(3+) or Gd~(3+) and co-doped with Sb~(3+) and Gd~(3+) were prepared by a solid-state reaction method. The phase purity, morphology, photoluminescence excitation and emission properties of the prepared phosphors were investigated. The results showed that Sb~(3+) could sensitize Gd~(3+) in the co-doped phosphors which made the phosphors excitable by short-wave ultraviolet(UV) at a wavelength between 220 and 260 nm. Under 253.7 nm excitation, the co-doped phosphors Y_(1–x–y) PO_4: Sb~(3+)x,Gd~(3+)y showed strong emission of Gd~(3+) at a wavelength of 312 nm whose intensity changed with the doping concentrations of Gd~(3+) and Sb~(3+). The optimized Y_(0.77)PO_4:Sb~(3+)0.07,Gd~(3+)0.16 phosphor showed an intensity comparable to commercial LaPO_4:Ce phosphor(UVB-315), making it a potential candidate for mercury low-pressure discharge narrow-band UV-B emitting lamps.     

Color tunable and white light emitting via energy transfer in single-phase BiOCl:Er3+,Sm3+ phosphors for WLEDs

BiOCl crystal shows potential as efficient optical host due to its special layered structure. Here,the luminescence properties of the Er~(3+)/Sm~(3+) co-doped BiOCl phosphors as single-phase phosphors were reported. Upon near ultraviolet excitation(NUV, 380 nm corresponding the ~4 I_(15/2)→ ~4 G_(11/2) transition of Er~(3+) ions), the phosphors exhibit the efficient characteristic emissions of Er~(3+) and Sm~(3+) ions simultaneously. The energy transfer(ET) from Er~(3+) to Sm~(3+) ions in the layered crystals has been validated by the variation of emission intensities and decay lifetimes respectively, which is ascribed to be a dipoledipole interaction. By virtue of the ET behavior and increasing Sm~(3+) ion concentration, the enhancing emission intensity of Sm~(3+) and the tunability of emission color from yellowish-green(0.318, 0.420) to white(0.343, 0.347) are realized. The results of our work indicate that the Er~(3+)/Sm~(3+) co-doped BiOCI phosphor has a promising application serving as single component white emitting phosphors for NUV excited WLEDs.     

Tunable emission properties of tri-doped Ca_9LiY_(2/3)(PO_4)_7:Ce~(3+),Tb~(3+),Mn~(2+) phosphors with warm white emitting based on energy transfer

Tri-doped Ca_9 LiY_(2/3)(PO_4)_7:Ce~(3+),Tb~(3+),Mn~(2+)phosphors were prepared by a high-temperature solid state method.Under UV light excitation,Ca_9 LiY_(2/3)(PO_4)_7:Ce~(3+)samples exhibit a broad band ranging from 320 to 500 nm.At 77 K,the emission spectra of Ca_9 LiY_(2/3)(PO_4)7:Ce~(3+)samples present two obvious emission peaks,indicating that Ce~(3+)ions occupy two different kinds of lattice sites(Ca(1/2) and Ca(3)),As a good sensitizer for Tb~(3+),Ce~(3+)ions in Ca_9 LiY_(2/3)(PO_4)_7 lattice can effectively transfer part of energy to Tb~(3+),and the energy trans fer mechanism is determined to be dipole-dipole interaction.Consequently,the emitting color for Ce~(3+) and Tb~(3+) co-doped Ca_9 LiY_(2/3)(PO_4)_7 samples can be tuned from bluish violet to green.In order to further enlarge the emission gamut,Mn~(2+)ions as red emission components were added,forming tri-doped single-phase Ca_9 LiY_(2/3)(PO_4)_7:Ce~(3+),Tb~(3+),Mn~(2+)phosphors.The Ca_9 LiY_(2/3)(PO_4)_7:Ce~(3+),Tb~(3+),Mn~(2+)phosphors exhibit tunable emission properties through controlling the relative doping concentration of Ce~(3+),Tb~(3+)and Mn~(2+).Especially,Ca_9 LiY_(2/3)(PO_4)_7:0.09 Ce~(3+),0.12 Tb~(3+),0.30 Mn~(2+)can emit warm white light.The sample shows good thermal stability.At 150℃,the emission intensity for Ce~(3+)(360 nm),Tb~(3+)(545 nm) and Mn~(2+)(655 nm) decreases to 63%,69%,and 72% of its initial intensity,respectively.Moreover,the sample obtains good stability after 10 cycles between room temperature and150℃.     

Synthesis and optical characterization of Eu2+,Tb3+-codoped Sr3Y(PO4)3 green phosphors

A series of Eu~(2+),Tb~(3+)-codoped Sr_3 Y(PO_4)_3(SYP) green phosphors were synthesized by hightemperature solid-state reaction. Several techniques, such as X-ray diffraction, UV-vis spectrum,and photoluminescence spectrum, were used to investigate the obtained phosphors. The present study investigates in detail photoluminescence excitation and emission properties, energy transfer between the two dopants, and effects of doping ions on optical band gap. SYP:0.05 Eu2+ phosphor shows an intense and broad excitation band ranging from 220 to 400 nm and exhibits a bright green emission band with CIE chromaticity coordinates(0.189, 0.359) under 350 nm excitation. Green emission of SYP:0.03 Tb3+ is intensified by codoping with Eu~(2+), and energy transfer mechanism between them is demonstrated to be a dipole-dipole interaction. Upon 350 nm excitation, SYP:Eu~(2+),Tb~(3+) phosphors exhibits two dominating bands peaking at 466 and 545 nm, which are assigned to 4 f~65 d~1→4 f~7 transition of Eu~(2+) ions and ~5 D_4→~7 F_5 transition of Tb~(3+) ions, respectively. Optimal doping concentrations of Eu~(2+) and Tb~(3+) in the SYP host are 5 mol% and 15 mol%, respectively. Results indicate that SYP:Eu~(2+),Tb~(3+) phosphors are potentially used as green-emitting phosphors for white light-emitting diodes.     

Photoluminescence characterization and energy transfer of NaBa1-x-yPO4：xCe3＋, yTb3＋ phosphors

A series of NaBa1-x-yPO4: xCe3+, yTb3+ phosphors were synthesized by solid-state reaction method. The crystal structure, photoluminescence emission and excitation spectra and decay times of the phosphors were carefully investigated. The results revealed that an efficient energy transfer occurred from Ce3+ to Tb3+ ions in NaBaPO4 host by means of dipole-dipole interactions and the critical distance of the energy transfer was about 0.638 nm. Moreover, the phosphor emitted strong green emission under UV excitation, indicating that the phosphors are potentially useful as a highly efficient, green-emitting phosphor.     

Influence of dysprosium concentration on sensitivity of luminescent thermometers of phosphors Ca_9Tb(PO_4)_5(SiO_4)F_2

Tb~(3+),Dy~(3+)-co-doped Ca_9 Tb_xDy_(1-x)(PO_4)_5(SiO_4)F_2 phosphors were prepared via high-temperature solidphase reaction method and the potential application in optical temperature measurements due to their color-tunable property was investigated in detail.The photoluminescence emission(PL) and photoluminescence excitation(PLE) spectra results show that the as-prepared phosphors exhibit both Tb~(3+) and Dy~(3+) emissions at 546 nm(~5 D_4-~7 F_5 transition of Tb~(3+)) and 587 nm(~4 F_(9/2)-~6 H_(13/2) transition of Dy~(3+)) upon376 nm excitation,respectively.In addition,the fluorescence decay analysis shows that the lifetime of the Tb3+emission rapidly decreases,which confirms the energy transfer existence between Dy~(3+) and Tb~(3+).Under 376 nm excitation,the temperature dependence of the fluorescence intensity ratios for the dualmission bands peaked at 546 and 587 nm was studied in the temperature range from 303 to 573 K.The results show that with the increase of Dy~(3+) concentration,the relative sensitivity first increases and then decreases,what's more,the maximum relative sensitivity is 3.142×10~(-3)%/K for Ca_9 Tb_xDy_(1-x)(PO_4)_5(SiO_4)-F_2(x=0.4).As a consequence,this preliminary study provides a novel method for exploring the novel thermo meters.     

Energy transfer,superior thermal stability and multi-color emitting properties of langbeinite-type solid-solution phosphor K_2Dy_(1.5-x)Eu_xTa_(0.5)(PO_4)_3

Langbeinite type compounds are a large kind of oxometallate with good flexibility structure.Herein,we synthesized a new langbeinite type compound K_2 Dy_(1.5)Ta_(0.5)(PO_4)_3,in which the Dy~(3+) and Ta~(5+) were blended to occupy the same crystallographic sites.Simultaneously,solid solutions of K_2 Dy_(1.5)_(-x)Eu_xTa_(0.5)(PO_4)_3(x=0-1.5) were prepared and their photoluminescence properties were investigated.Due to energy transfer from Dy~(3+) to Eu~(3+),both Dy~(3+) and Eu~(3+) characteristic emissions are observed under 393 nm light excitation.The emitting color of K_2 Dy_(1.5-x)Eu_xTa_(0.5)(PO_4)_3 turns from green through yellow to red by simply adjusting the Eu~(3+) concentration from 0 to 0.4.Moreover,K_2 Dy_(1.48)Eu_(0.02)Ta_(0.5)(PO_4)_3 phosphor possesses excellent fluorescence thermal stability and exhibits zero thermal quenching at 150 ℃.These results manifest that K_2 Dy_(1.5-x)Eu_xTa_(0.5)(PO_4)_3 solutions are promising multi-color emitting phosphors candidate for near-UV LED.     

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...     

High thermal stability and quantum yields of green-emitting Sr_3Gd_2(Si_3O_9)_2:Tb~(3+) phosphor by co-doping Ce~(3+)

A series of Tb~(3+) mono-doped and Ce~(3+)-Tb~(3+) co-doped Sr_3Gd_2(Si_3O_9)_2 phosphors with high thermal stability and quantum yields were successfully prepared via the solid state reaction. The as-prepared Sr_3Gd_2(Si_3O_9)_2:Tb~(3+) samples showed broad excitation spectrum from 250 to 400 nm and presented characteristic emission transitions ~5D_4→~7F_J(J=6, 5, 4, 3) of Tb~(3+) under 313 nm excitation, which were located at about 488, 541, 584 and 620 nm. The emission intensities of Tb~(3+) rose steadily in Sr_3Gd_2(Si_3O_9)_2 host with the increase of Tb~(3+) concentration even though Gd~(3+) ions were completely replaced by Tb~(3+) ions. The Ce~(3+) ion as a sensitizer could efficiently improve the performance of Tb~(3+) ion. First, with Ce~(3+) co-doping, the excitation spectrum of Tb~(3+) monitored at 541 nm showed a similar band that responds to the violet emission of Ce~(3+) monitored at 416 nm. Second, the quantum yields of Sr_3Gd_2(Si_3O_9)_2:Tb~(3+) phosphors could be enhanced from 26.6% to 80.2% by co-doping Ce~(3+). Finally, the co-doping of Ce~(3+) was also effective to improve the thermal stability of Sr_3Gd_2(Si_3O_9)_2:Tb~(3+). As the temperature rose to 150 oC, the emission intensity of Tb~(3+) remained at about 83.6% of that measured at room temperature, which was better than the commercial YAG:Ce phosphor in terms of their thermal quenching properties. These results indicated that the as-prepared Sr_3Gd_2(Si_3O_9)_2:Tb~(3+),Ce~(3+) samples could be used as green emission phosphors for possible applications in near ultraviolet based WLEDs.     

Reddish orange long lasting phosphorescence of Sm3+ in Sr2ZnSi2O7:Sm3+ phosphors

Long lasting phosphorescence phosphors with composition of (Sr1-xSmx)2ZnSi2O7 were prepared by conventional high-temperature solid-state method. Their properties were systematically investigated utilizing XRD, photoluminescence, phosphorescence and thermoluminescence spectra. The results showed that these phosphors emitted reddish orange light that corresponds to the characteristic emission due to the 4G5/2→6H5/2, 6H7/2 and 6H9/2 transitions of Sm3+. After the UV light excitation source was switched off, th...     

White light-emitting Ba0.05Sr0.95WO4:Tm3+ Dy3+ phosphors

Tm~(3+) and Dy~(3+) co-doped Ba_(0.05)Sr_(0.95)WO_4 phosphors were synthesized by a low temperature combustion method. The structures of the samples were SrWO_4 phase and were identified by X-ray diffraction. The surface topographies of Ba_(0.05)Sr_(0.91)WO_4:0.01 Tm~(3+) 0.03 Dy~(3+) were tested by scanning electron microscopy. The particles are ellipsoid, and their average diameter is approximately 0.5 μm. The emission spectra of Ba_(0.05)Sr_(0.95)WO_4:Tm~(3+) show a peak at 454 nm which belongs to the ~3 H_6→~1 D_2 transition of Tm~(3+), and the optimum doping concentration of Tm~(3+) ions was 0.01. The emission spectra of Ba_(0.05)Sr_(0.95)WO_4:Dy~(3+) consist of the ~4 F_(9/2)→~6 H_(13/2) dominant transition located at 573 nm, the weaker ~4 F_(9/_2→~6 H_(15/2) transition located at 478 and 485 nm. and the weakest ~4 F_(9/2)→~6 H_(11/2) transition located at660 nm, and the optimum doping concentration of Dy~(3+) ions was 0.05. A white light is achieved from Tm~(3+) and Dy~(3+) co-doped Ba_(0.05)Sr_(0.95)MoO_4 crystals excited at 352-366 nm. With the doping concentration of Tm~(3+) fixed at 0.01, the luminescence of Ba_(0.05)Sr_(0.95)MoO_4:Tm~(3+)Dy~(3+) is closest to standard white-light emissions when the concentration of Dy~(3+) is 0.03; the chromaticity coordinates are(0.321,0.347), and the color temperature is 6000 K.