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Multicolor emitting phosphors LiBaPO4:RE (RE = Eu2+, Tb3+, Sm3+) reported as interesting down-conversion luminescent materials in white light-emitting diodes (w-LEDs) have been prepared by a conventional solid-state reaction. The excitation and emission spectra indicate that these phosphors can be effectively excited by the near-UV light, and emit blue, green, and red light, respectively. The photoluminescence properties, decay times, and Commission Internationale de I'Eclairage (CIE) chromaticity indexes are determined for various concentrations of the activators Eu2+, Tb3+, and Sm3+ in LiBaPO4 host. Furthermore, the temperature-dependent luminescence of these phosphors was investigated. The emission intensities of Tb3+- and Sm3+-doped LiBaPO4 increased unexpectedly with increasing temperature. This interesting phenomenon is proposed to be the result of two ground states in the configurational coordination diagram. The present investigation suggests that LiBaPO4:RE (RE = Eu2+, Tb3+, Sm3+) were potential candidates for application in w-LEDs. [ABSTRACT FROM AUTHOR]

In this study, Ba2Y1−xTaO6:xEu3+ (BY1−xT:xEu3+; x = 0.03–0.20), as a double perovskite orange-red-emitting phosphor, was synthesized by solid-state reaction. The prepared phosphor samples were characterized by XRD, SEM, photoluminescence spectra, temperature-dependent photoluminescence spectra and decay curve measurements. The X-ray diffraction patterns indicated that the phosphor is a pure phase of a double perovskite structure [space group Fm-3m (225)]. Upon near-ultraviolet excitation, the sample exhibited a strong orange-red emission at 592 nm due to the 5D0 → 7F1 transition, which revealed that the Eu3+ ions were located at the central symmetric lattice position. The critical concentration of Eu3+ ions in Ba2YTaO6 (BYT) was determined to be 12 mol.%. The as-prepared phosphors showed excellent thermal stability according to temperature-dependent emission spectroscopy. The CIE values of BY1−xT:xEu3+ phosphors were found to be located in the red region. These results suggested that the prepared BY1−xT:xEu3+ phosphors will have a potential application in white light emitting diodes (WLEDs). [ABSTRACT FROM AUTHOR]

A novel Sr2Y1−xTaO6:xEu3+ (x = 0.04-0.20) red-emitting phosphor was synthesized by using the conventional solid-state reaction method. The crystal structure, photoluminescence properties, thermal stability and decay lifetimes were investigated in detail. Upon near UV light excitation, this sample exhibited a strong red emission peak centered at 612 nm due to 5D0 → 7F2, which indicated that Eu3+ occupies low symmetry sites within the Sr2YTaO6 host lattice. The optimized doping concentration of Eu3+ ion is about 12 mol%. The excellent thermal stability of Sr2YTaO6:Eu3+ phosphor was tested according to the temperature dependent emission spectra. In addition, the Sr2Y1−xEuxTaO6 phosphors exhibited good color coordinate (0.6076, 0.3879) and high color purity about 84.55%. All results indicated that the Sr2Y1−xTaO6:xEu3+ phosphors can serve as an efficient red phosphor in the white light emitting diodes. [ABSTRACT FROM AUTHOR]

A series of SrLu(PO): xSmphosphors were synthesized via a conventional solid-state reaction method. The prepared phosphors were investigated using X-ray diffraction and Scanning electron microscopy. The excitation and emission spectra, concentration quenching mechanism, and fluorescence decays of the phosphors were also measured and discussed. Under 403 nm excitation, the G → H (J = 5/2, 7/2, 9/2, and 11/2) emissions of Sm were obviously observed with peaks located at 564, 599, 646 and 705 nm, respectively. The optimum dopant concentration of Sm ions in SrLu(PO) is 3 mol% and the corresponding Commission Internationale deL'Eclairage chromaticity coordinate of the SrLu(PO):0.03Sm phosphor was located in the orange reddish region. In addition, the temperature dependent luminescence and the absolute quantum efficiency of the typical sample was also investigated. The results confirmed that the as-synthesized SrLu(PO):Sm phosphors can act as a suitable candidate of the warm components of near-ultraviolet white light-emitting diodes. [ABSTRACT FROM AUTHOR]

Single-component-tunable blue-to green-light-emitting phosphors BaSr(BO)F: Ce, Tb, Na (BSBF: Ce, Tb, Na) promising for near-UV-pumped light-emitting diodes (LEDs) were synthesized via high-temperature solid-state reactions, and their photoluminescence properties were systematically investigated. Upon the excitation of 360 nm, the BSBF: Ce, Tb, Na phosphors exhibited a broad blue emission band at 422 nm and a series of sharp emission lines at 490, 544, 585, and 623 nm, which originated from the 4 f5 d-4 f transition of Ce ions, and D- F ( J = 6, 5, 4, 3) transitions of Tb ions, respectively. Through the resonance-type energy transfer, the varied emitted colors from blue through cyan and eventually to green were achieved by properly tuning the relative dopant composition of Ce/Tb. Moreover, the energy transfer from Ce to Tb in BSBF host matrix was demonstrated via the dipole-dipole interaction mechanism. Additionally, the critical distances ( $$ R_{\text{C}} $$ ) calculated by quenching concentration and spectral overlap method in such system were 2.166 and 1.940 nm, and the activation energy for thermal quenching (Δ E) was determined to be 0.117 eV. These results indicate that the developed color-tunable phosphors BSBF: Ce, Tb, Na are competitive as the promising single-component phosphor-converted materials for near-UV-pumped LEDs. [ABSTRACT FROM AUTHOR]

Sr 3 (Gd 1− x Dy x )(PO 4 ) 3 phosphors for white light-emitting diodes (w-LEDs) were prepared by the conventional solid-state reaction. X-ray diffraction (XRD) and photoluminescence spectra were utilized to characterize the structure and luminescence properties of the as-synthesized phosphors. Luminescence properties shows that the phosphor can be efficiently excited by the ultraviolet visible light in the region from 300 to 450 nm, and it exhibits blue (483 nm) and yellow (575 nm) emission corresponding to 4 F 9/2 → 6 H 15/2 transition and 4 F 9/2 → 6 H 13/2 transition, respectively. It has been found that concentration quenching occurs via dipole–dipole interaction according to Dexter׳s theory. The temperature dependence of photoluminescence properties is investigated from 25 to 250 °C and the prepared Sr 3 Gd(PO 4 ) 3 :Dy 3+ phosphors show good thermal quenching properties. [ABSTRACT FROM AUTHOR]

A series of yellow-emitting Na 2 (Ba 2 −x Sm x )Si 2 O 7 phosphors have been prepared via solid-state reaction technique. X-ray diffraction (XRD), photoluminescence (PL) spectra, temperature-dependent luminescence property, concentration quenching mechanism and luminescence lifetime are applied to characterize the obtained samples. Under 402 nm near ultraviolent excitation, the samples emit yellow light and the color purity is close to 100%. The critical quenching concentration of Sm 3+ in the Na 2 Ba 2 Si 2 O 7 host is about 3.6 mol% and corresponding quenching behavior is ascribed to be electric dipole–dipole interaction. Furthermore, the phosphor has good thermal stability property, superior to the commercial yellow Y 3 Al 5 O 12 :Ce 3+ phosphor and the activation energy for thermal quenching is calculated as 0.18 eV. [ABSTRACT FROM AUTHOR]

Abstract: A series of new luminescent emission-tunable phosphors Sr3Gd(PO4)3(SGP):0.006Ce3+, xMn2+ have been synthesized by a high-temperature solid-state reaction. The energy transfer from Ce3+ to Mn2+ in SGP:Ce3+/Mn2+ phosphors has been validated and demonstrated to be a resonant type via a dipole–quadrupole mechanism based on the decay lifetime data, and the critical distance (R C ) calculated by quenching concentration method and spectral overlap method are 25.24 and 24.26Å, respectively. Tuning the Ce3+/Mn2+ ratio via the energy transfer varied the emission hue of from blue to white-light and eventually to yellow. These results indicate that the developed phosphor may be promising as a single-component white-light-emitting phosphor for white LEDs. [Copyright &y& Elsevier]

Abstract: Novel Y2Si4N6C:Sm3+ phosphors for white light-emitting diodes (w-LEDs) were prepared by a carbothermal reduction and nitridation method. X-ray diffraction (XRD) and photoluminescence spectra were utilized to characterize the structure and luminescence properties of the as-synthesized phosphors. The emission spectrum obtained by excitation into 291nm contains exclusively the characteristic emission of Sm3+ at 568, 607 and 654nm which correspond to the transitions from 4G5/2 to 6H5/2, 6H7/2, and 6H9/2 of Sm3+, respectively. The strongest one is located at 607nm due to 4G5/2–6H7/2 transition of Sm3+. It was found that concentration quenching occurred as a result of dipole–dipole interaction according to Dexter''s theory. The temperature dependence of photoluminescence properties was investigated from 25 to 300°C and the prepared Y2Si4N6C:Sm3+ phosphors showed superior thermal quenching properties. [Copyright &y& Elsevier]

Abstract: Novel blue/green NaSrPO4 phosphors co-doped with Eu2+ and Tb3+ were synthesized by a conventional solid-state reaction. Their luminescent properties were characterized by using powder X-ray diffraction, photoluminescence excitation and emission spectra, lifetime, and temperature dependent emission spectra, respectively. The NaSrPO4:Eu2+,Tb3+,Na+ phosphor showed an intense broad excitation band between 250 and 430nm, which was in agreement with the near-UV chip (350–420nm), and it exhibited two dominating emission bands at 445 and 545nm, corresponding to the allowed 4f65d1→4f7(8S7/2) transition of Eu2+ ion and the 5D4→7F5 transition of Tb3+ ion, respectively. The emission intensity and lifetime of Eu2+ ion decreased with the increasing concentration of Tb3+ ion, which strongly indicated that an effective energy transfer occurred from Eu2+ to Tb3+ in NaSrPO4 host. The principle of the energy transfer should be the combined effect of the non-radiative resonant energy transfer and the phonon-assisted non-radiative process. [Copyright &y& Elsevier]

Abstract: Novel LiSrPO4:Dy3+ phosphors for white light-emitting diodes (w-LEDs) were synthesized by the conventional solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the phase formation of LiSrPO4:Dy3+ materials. Luminescence properties results showed that the phosphor could be efficiently excited by the UV–vis light region from 250 to 460nm, and it exhibited blue (483nm) and yellow (574nm) emission corresponding to 4F9/2 → 6H15/2 transitions and 4F9/2 → 6H13/2 transitions, respectively. The luminescence intensity of LiSrPO4:xDy3+ phosphor firstly increased and then decreased with increasing Dy3+ concentration, and reached the maximum at x =0.03. It was found that concentration quenching occurred as a result of dipole-dipole interaction according to the Dexter''s theory. The decay time was also determined for various concentrations of Dy3+ in LiSrPO4. [Copyright &y& Elsevier]

Sr 3−2 x Sm x Na x B 2 SiO 8 phosphors were synthesized by the solid-state reactions. X-ray diffraction, diffuse reflection, photoluminescence excitation and emission, as well as fluorescence decay measurements were utilized to investigate the structural and spectral properties of the samples. The results indicated that Sr 3−2 x Sm x Na x B 2 SiO 8 phosphors could be efficiently excited by the near-ultraviolet light to realize a novel reddish orange luminescence corresponding to the characteristic transitions 4 G 5/2 → 6 H J (J = 5/2, 7/2, 9/2, 11/2) of Sm 3+ ions, with a maximum intensity at 600 nm. Based on the theoretical calculation, the dipole–dipole interaction was dominantly involved concentration quenching of Sm 3+ in the phosphors, and the critical transfer distance ( R c ) was determined to be 13.59 Å. Furthermore, Judd-Ofelt analysis was applied to evaluate three phenomenological Judd-Ofelt intensity parameters ( Ω λ , λ = 2, 4, 6), and in turn radiative properties such as radiative transition probabilities ( A R ), radiative lifetimes ( τ R ) and fluorescence branching ratios ( β R ) for the excited 4 G 5/2 luminescent level of Sm 3+ ions were determined. Upon 402 nm excitation, the composition-optimized Sr 2.90 Sm 0.05 Na 0.05 B 2 SiO 8 exhibited the preferable photoluminescence intensity and CIE coordinates of (0.534, 0.448). These results suggest that the Sm 3+ -doped Sr 3 B 2 SiO 8 phosphors are competitive as the reddish orange-emitting phosphor-converted materials for application in near-ultraviolet-pumped LEDs. [ABSTRACT FROM AUTHOR]

Abstract: A blue-emitting Ca2B5O9Br:Eu2+ phosphor for white light-emitting diodes was synthesized via a microwave calcination route. The phosphor powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectrophotometer, respectively. The obtained results revealed that the Ca2B5O9Br:Eu2+ phosphor prepared by the microwave calcination route possessed a rod-like morphology with the single phase orthorhombic structure. Based on the photoluminescence analysis, it was found that Ca2B5O9Br:Eu2+ phosphor exhibited a broad excitation band chiefly in the near ultraviolet region (270–420nm) and a blue broad emission band of main peak at 452nm under the strongest excitation of 411nm. Further investigation on concentration-dependent emission spectra indicated that Ca2B5O9Br:0.03Eu2+ phosphor exhibited the strongest luminescent intensity, and the concentration quenching for the two Eu-site emission centers was caused by dipole–dipole interactions. [Copyright &y& Elsevier]

Highlights • SrZnO 2 has self-excitation luminescence properties. • Excitation properties of SrZnO 2 were regulated by doping Ca2+ ions. • Excitated at 374 nm, Sr 0.85 Ca 0.15 ZnO 2 :Eu3+ obtains a broad emission band. • Tunable red-emitting was realized by doping Ca2+ ions into SrZnO 2 :Eu3+. • Sr 0.85 Ca 0.15 ZnO 2 :Eu3+ obtains the red emission with 90.05% color purity. Abstract A series of Sr 1− x Ca x ZnO 2 :0.02 Eu3+ phosphors have been prepared by solid-state method. The effects of Ca2+ ions on luminescent properties of SrZnO 2 :0.02 Eu3+ have been systematically investigated by X-ray diffraction (XRD) patterns, the photoluminescence excitation and emission spectra, and International Commission on Illumination (CIE) chromaticity diagram. The red-emitting of Eu3+ doped Sr 1− x Ca x ZnO 2 phosphors can be tuned based on the host-sensitized luminescence effect, in which the maximum emission intensity and 90.05% color purity at 396 nm excitation, a broad emission band ranging from 475 to 800 nm at 374 nm excitation have been achieved in the Sr 0.85 Ca 0.15 ZnO 2 :0.02 Eu3+ sample, which demonstrate the occurrence of energy transfer from host to Eu3+ ions. Therefore, Eu3+ doped Sr 1− x Ca x ZnO 2 phosphors will become a promising candidate as a new single-host red-emitting phosphor for white LEDs applications. [ABSTRACT FROM AUTHOR]

Abstract A series of Eu2+ and/or Tb3+ doped Sr 3 NaSc(PO 4) 3 F phosphors were prepared under a high temperature solid-state reaction. The crystal structure and morphology of the phosphors were characterized by the X-ray diffraction and field emission scanning electron microscopy. Blue phosphor Sr 3 NaSc(PO 4) 3 F:Eu2+ has the high quantum efficiency and can be excited by the intense broad excitation from 220 to 420 nm, matching well with the commercial near-UV chips. The photoluminescence properties and quantum efficiency are substantially improved by the doping of Eu2+ ions into the Sr 3 NaSc(PO 4) 3 F:Tb3+ phosphors, which is attributed to the efficient energy transfer from Eu2+ to Tb3+. Furthermore, the energy transfer process from Eu2+ to Tb3+ in Sr 3 NaSc(PO 4) 3 F is demonstrated by fluorescence spectra and decay time, where a resonant type via a dipole-dipole mechanism was demonstrated. In addition, the color tunable emission from blue to green can be realized by adjusting the Eu2+/Tb3+ ratio. The temperature-dependent photoluminescence results of as-prepared samples revealed that the Sr 3 NaSc(PO 4) 3 F:Eu2+ and Sr 3 NaSc(PO 4) 3 F:Eu2+,Tb3+ phosphors have excellent thermal stability, being available to near-UV LEDs. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Na 2 BaMgP 2 O 8 :Eu 2+ , Tb 3+ phosphors were synthesized via a solid-state reaction method and their phase structures were carefully studied by powder X-ray diffraction (XRD) and detailed Rietveld refinement, respectively. Upon excitation with a wavelength at 365 nm, the as-obtained phosphors exhibited two characteristic emission bands ascribed to the allowed 4f–5d transition of Eu 2+ ion and the 5 D 4 − 7 F J ( J = 6, 5, 4, 3) transition of Tb 3+ ion, respectively. The emission intensities and lifetime values of Eu 2+ emission for Na 2+ y Ba 0.99−2 y MgP 2 O 8 :0.01Eu 2+ , y Tb 3+ phosphors decreased with increasing the concentration of Tb 3+ ion, which strongly verified that an effective energy transfer occurred from Eu 2+ to Tb 3+ in Na 2 BaMgP 2 O 8 host. [ABSTRACT FROM AUTHOR]

Abstract: A novel green emitting phosphor, Eu2+-activated Ca6Sr4(Si2O7)3Cl2, was synthesized using the solid-state reaction and its temperature-dependent luminescence characteristic was reported for the first time. Crystallographic site-occupations of Eu2+ ions in this host were assigned and two distinguishable Sr2+ sites were confirmed. As the temperature increases, the emission lines of Ca6Sr3.99(Si2O7)3Cl2:0.01Eu2+ show an anomalous blue-shift along with the broadening bandwidth and decreasing emission intensity, which is ascribed in terms of the phonon-assisted back tunneling from the excited state of low-energy emission band to the high-energy emission band in the configuration coordinate diagram. Further, the luminescence quenching temperature, the activation energy for thermal quenching (ΔE), and the chromaticity coordinates were also investigated. In view of its preferable excitation spectrum profile, intense green emission peaking at 511nm, and high thermal luminescence stability, the as-prepared phosphor is expected to find applications as a new green emitting phosphor for near-UV light emitting diodes. [Copyright &y& Elsevier]

Single-phased Sr 3 NaY(PO 4) 3 F:Ce3+, Mn2+ phosphors were synthesized by solid-state reaction method. The X-ray powder diffraction (XRD), photoluminescence (PL) spectrum and energy transfer from Ce3+ to Mn2+ of the samples were investigated. The PL spectrum of Sr 3 NaY(PO 4) 3 F:Ce3+, Mn2+ show there is a wide hump in the range of 300 to 450 nm of Ce3+ ions and characteristic peak of Mn2+ ions. The emission intensity of Mn2+ increased and that of Ce3+ decreased with increasing Mn2+ concentration. The color-tunable of the Sr 3 NaY(PO 4) 3 F:Ce3+, Mn2+ phosphors adjust from blue to yellow by changing the Mn2+ doping concentration. The decay curves show that energy transfer mechanism between Ce3+ and Mn2+ is quadrupole-quadrupole interaction. Moreover, the Sr 3 NaY(PO 4) 3 F:Ce3+, Mn2+ phosphors exhibit excellent thermal stability. Based on obtained results, the Sr 3 NaY(PO 4) 3 F:Ce3+, Mn2+ phosphors can act as efficient candidate phosphors materials for NUV-pumped white light-emitting diodes. [ABSTRACT FROM AUTHOR]