Phosphors For White LED Applications Research Articles

Novel Tm3+/Dy3+ co-doped CaMoO4 transparent glass-ceramic phosphor for white LED applications

To develop new inorganic luminescent materials, a set of Dy3+/Tm3+ co-doped molybdate precursor glasses (PGs) were manufactured using the conventional melting method, and a novel CaMoO4 transparent fluorescent glass-ceramic (GC700-2 h) was achieved via controlled crystallization of PG at 700 ℃ for 2 h. The luminescent color of the glass phosphor was facilely modulated by varying the doping levels of Dy3+ and Tm3+. The glass phosphor with optimal doping concentration of 0.6Dy3+ and 0.6Tm3+ exhibits a color coordinate of (0.3334, 0.3107). Compared with PG, the luminous intensity and quantum yield of GC700-2 h sample is obviously increased, and GC720-2 h sample displays the color coordinate (0.3292, 0.2852), belonging to the standard white light region. Moreover, GC720-2 h sample possesses good thermal stability in fluorescence property. The white LED lamp encapsulated with GC720-2 h exhibits color temperature of 7564 K and color rendering index of 75.3. These results clearly show that the 0.6Dy3+/0.6Tm3+ co-doped glass and CaMoO4 glass-ceramic could be used as potential candidate material in the field of white light-emitting diodes.

A novel n-UV convertible colour-tunable emitting oxynitride phosphor: Realization based on Ce3+ -Tb3+ energy transfer.

In the present work, a novel n-UV convertible colour-tunable emitting phosphor was obtained based on the efficient Ce3+ -Tb3+ energy transfer in the Y10 Al2 Si3 O18 N4 host. By properly controlling the ratio of Ce3+ /Tb3+ , the colour hue of the obtained powder covered the blue and green regions, under excitation of 365 nm. The steady-state and dynamic-state luminescence measurement was performed to shed light on the related mechanism, which was justified by the electronic dipole-quadrupole dominating the related energy transfer process. Preliminary studies showed that Y10 Al2 Si3 O18 N4 :Ce3+ ,Tb3+ can be promising as an inorganic phosphor for white LED applications.

Exploration of efficient photoluminescence properties of intense green emitting Er3+ activated NaBi(MoO4)2 phosphor for white LED applications

Exploration of efficient photoluminescence properties of intense green emitting Er3+ activated NaBi(MoO4)2 phosphor for white LED applications

Synthesis and photoluminescence properties of novel orange-emitting Ba2Gd8(SiO4)6O2: Sm3+ phosphors for white LED applications

The solid-state method was utilized to prepare a series of orange-red-emitting Sm3+-doped Ba2Gd8(SiO4)6O2 phosphors. The X-ray powder diffraction patterns indicated that the synthesized phosphors had a pure hexagonal phase. X-ray energy dispersive spectroscopy studies confirmed the elemental composition and distribution of the different elements present in the Ba2Gd8 (SiO4) 6O2: Sm3+ powder. The Sm3+-doped Ba2Gd8 (SiO4) 6O2 phosphors exhibited bright luminescence under 407 nm excitation, with a primary peak at 600 nm. Spectral analysis showed that the Sm3+-doped Ba2Gd8 (SiO4) 6O2 phosphors emitted bright orange-red light. Concentration quenching was detected in Sm3+-doped Ba2Gd8(SiO4)6O2 phosphors with a 0.03 mol% concentration of Sm3+ ions because of the multipolar interaction between the two closest Sm3+ ions. The effective orange-red emission suggests the use of Sm3+-doped Ba2Gd8(SiO4)6O2phosphors for white light-emitting diodes.

Energy transfer induced colour tunable photoluminescence performance of thermally stable Sm3+/Eu3+ co-doped Ba3MoTiO8 phosphors for white LED applications

Energy transfer induced colour tunable photoluminescence performance of thermally stable Sm3+/Eu3+ co-doped Ba3MoTiO8 phosphors for white LED applications

Photoluminescence properties and energy transfer in the color tunable Ba2CaZn2Si6O17:Bi3+, Tb3+, Eu3+ silicate phosphor for white LED applications

A series of Bi3+, Tb3+, and Eu3+ ions doped (separately, and together) with the Ba2CaZn2Si6O17 (here after called BCZSO) silicate host were prepared by using the solid-state reaction technique. The phase formation and the morphology analysis of this phosphor were investigated by using powder X-ray diffraction (PXRD) patterns, and scanning electron microscope (SEM) images. When excited with 291 nm, the BC1-x-yZSO:xBi3+, yTb3+phosphor revealed a broad blue emission centered at 465 nm (due to Bi3+ ions) accompanied by a few sharp peaks at 487, 545, 585, and 624 nm pertaining to the characteristic transitions of the Tb3+ ions. The BC1-x-y-zZSO:xBi3+, yTb3+, zEu3+ phosphor, when excited at 281 nm, emitted a wide band centered at 465 nm due to the Bi3+ ions, along with a few narrow bands due to other co-dopants. The 545 nm emission band is due to the Tb3+ ions, and the bands at 593, 611, 653, and 704 nm are the characteristic transitions of the Eu3+ ions. The efficiency of the energy transfer from the sensitizer Bi3+ ions to the activator Tb3+ ions was investigated. The critical distance Rc between the Bi3+, and the Tb3+ ions was obtained to be 17.98 Å, with respect to the concentration quenching effect. The decay time analysis of the phosphors showed a decreasing trend with increase in the concentration of the activator ions. The CIE chromaticity color coordinates, and the correlated color temperature of these phosphors were calculated. Due to the presence of the Bi3+, and the Tb3+ ions, the color coordinates fall in the bluish white region. Further, the Eu3+ ions when co-doped with the Bi3+/Tb3+ ions, the emission color was shifted towards the near white region. The quantum efficiency of the samples were also measured. The temperature dependent photoluminescence (TDPL) was done for this phosphor, and the corresponding activation energy value of the phosphor was 0.206 eV. These results suggest that the BC1-x-y-zZSO:xBi3+, yTb3+, zEu3+ phosphor can serve as a good candidate in white light emitting diodes (WLEDs) applications.

Synthesis and luminescence properties of novel SrScLiTeO6:Ln (Ln = Eu3+, Sm3+) phosphors for white LED applications

Novel Eu3+ or Sm3+ ions doped SrScLiTeO6 phosphors were successfully prepared by a solid-state reaction, and the phase formation, crystal structure and luminescence properties of the samples were studied in detail. Under the excitation of 394 nm, the SrScLiTeO6:Eu3+ phosphors show the strongest emission peak located at 615 nm corresponding to the electric dipole 5D0 → 7F2 transition. The SrScLiTeO6:Sm3+ phosphors show orange–red light upon near-ultraviolet (n-UV) excitation, and the strongest emission peak occurs at 597 nm, corresponding to the 4G5/2 → 6H7/2 transition. The critical quenching concentrations of Eu3+ and Sm3+ ions in the SrScLiTeO6 phosphors were about 0.08 mol and 0.02 mol, and the corresponding concentration quenching mechanisms were verified to be the dipole–dipole interaction. Due to the different energy transfer between different energy levels, the decay times of Eu3+ and Sm3+ ions are different. The fluorescent thermal quenching studies showed the SrScLiTeO6:Sm3+ phosphors had high thermal-stable properties. The above results indicate that synthetic phosphors have potential application in white light emitting diodes (w-LEDs).

Near-UV-excited Dy3+-doped calcium borophosphate (CBP) phosphors for white LED applications

Calcium borophosphate (CBP) phosphors doped with Dy3+ were synthesized by solid-state reaction method. These phosphors were characterized by photoluminescence spectra and decay curves in the visible region. These phosphors were excited at 350 nm, and emission spectra were studied. Decay curves were obtained for the transition, 4F9/2 → 6H13/2 of Dy3+, and lifetimes were measured for different concentrations of Dy3+ ions. CIE chromaticity coordinates were obtained for these Dy3+-doped CBP phosphors. Correlated color temperature was also calculated using the standard formula.

Novel reddish-orange color emitting Ca2SiO4:Sm3+ phosphors for white LED applications prepared by using agricultural waste

Ca2SiO4:Sm3+ phosphors, where CaO and Si2O are synthesized from agricultural waste, are prepared through regular solid state reaction (SSR) technique. The XRD pattern confirmed their monoclinic structure and well matches with ICDD card No. 01-076-3612. The morphological studies through SEM images reveal that these were irregular in size and shape. Decay rates, emission and excitation spectra are measured to estimate the luminescent characteristics of Ca2SiO4:Sm3+ phosphors. The CIE chromaticity values are evaluated and it is shown in reddish-orange region. The luminescence is quenched for doping concentration of above 0.2 mol % of the Sm3+ ion owing to energy transfer through non-radiative process among the Sm3+ ions at different sites. The decay curves are exhibit near single exponential nature for lower (≤0.1 mol %) Sm3+ ion concentrations and turns in to non-exponential nature for higher (≥0.2 mol %) Sm3+ ion concentration. The lifetime values are increasing from 1.67 to 2.28 ms with decrease in concentration of Sm3+ ions from 0.3 to 0.01 mol %. These results suggest that the Ca2SiO4:Sm3+ phosphors were appropriate candidate for low cost white LED applications.

Broad greenish-yellow luminescence in CaMoO4 by Si4+ acceptor doping as potential phosphors for white light emitting diode applications

Intense broad greenish-yellow luminescence has been observed in CaMoO4 by Si4+ acceptor doping. The broad intense luminescence is attributed to the increased charge transfer transitions in MoO42− groups and defect luminescence due to distortion and defects. The Si4+ doping acts on two fronts, distorting the MoO4 tetrahedron and inducing oxygen vacancies promoting acceptor levels near the VB edge. The XPS core level spectra analysis indicates an asymmetric broadening of the peaks with an increase of fwhm suggesting defects and oxygen vacancies in the system. The defect and charge transfer luminescence increases competitively with Si4+ doping. The lifetime of the defect luminescence increases with Si4+ doping which suggests the increased radiative emissive transitions without quenching. These factors broadened the luminescence covering the most visible region (425–625 nm) enhancing the fwhm. The calculated CIE chromaticity coordinates fall in the greenish-yellow region with values (0.31, 0.45) making them potential phosphors for white LED applications.

Correction to: Sol–gel synthesis and luminescence properties of CaGd2(MoO4)4:Pr3+ phosphors for white LED applications

The original version of the article was published without the first author contact details.

Sol–gel synthesis and luminescence properties of CaGd2(MoO4)4:Pr3+ phosphors for white LED applications

A series of novel red emitting CaGd2(MoO4)4:xPr3+ (x = 0.005–0.045) micro phosphors were successfully prepared via a simple citrate assisted sol–gel method-ray powder diffraction, scanning electron microscope, photoluminescence spectra and decay life time measurement were utilized to study the properties of CaGd2(MoO4)4:xPr3+ phosphors well crystallized, fine and homogenous micro particles appeared at the heat treatment at 900 °C for 6 h. The results confirms that CaGd2(MoO4)4 host has tetragonally distorted scheelite structure with space group I41/a. Under the excitation wavelength of 449 nm Pr3+ activated CaGd2(MoO4)4 phosphor shows the red emission peaked at about 649 nm, which is attributed to 3P0–3F2 transition of Pr3+ ions. The CIE co-ordinates of CaGd2(MoO4)4:0.035Pr3+ phosphor are x = 0.702 and y = 0.289, which are evidently close to the standard NSTC value. The luminescence properties of as prepared phosphors indicates that CaGd2(MoO4)4:xPr3+ phosphor may be a potential red emitting material for W-LED applications.

Synthesis and photoluminescence properties of red-emitting NaLaMgWO6:Sm3+,Eu3+ phosphors for white LED applications

A series of red-emitting NaLaMgWO6:Sm3+,Eu3+ phosphors were successfully synthesized by the solid-state reaction method. The crystal structure, morphology and photoluminescence properties were investigated in detail. The NaLaMgWO6 compound has monoclinic structure with the space group C2/m. Upon excitation of the near-ultraviolet light, the Sm3+ singly doped and Eu3+singly doped phosphors exhibit red emission at 600 nm (4G5/2→6H7/2 transition of Sm3+) and 617 nm (5D0→7F2 transition of Eu3+), respectively, while the Sm3+, Eu3+ co-doped phosphors show the characteristic transition of Eu3+ whether excited by 397 or 406 nm. This indicates the existence of the energy transfer from Sm3+ to Eu3+ ions. Furthermore, the mechanism of energy transfer and energy transfer efficiency were confirmed by the decay time of Sm3+ ion in NaLaMgWO6:Sm3+,Eu3+ phosphors. The mechanism of energy transfer between Sm3+ and Eu3+ is proved to be dipole-dipole interaction, and the energy transfer efficiency of NaLa0.65MgWO6:0.05Sm3+,0.3Eu3+ phosphor is calculated to be 38.89%. The temperature dependent emission spectra demonstrate that the NaLaMgWO6:Sm3+,Eu3+ phosphor has a good thermal stability with an thermal activation energy ΔE of 0.241 eV. The CIE chromaticity coordinate is calculated to be (x = 0.661, y = 0.339).

Near UV excited SrAl2O4:Dy3+ phosphors for white LED applications

Strontium aluminate phosphors containing different concentrations of Dy3+ ions (SrAl2O4:Dy3+) were prepared by solid state reaction method by sintering at 1100 °C for 3 h. These phosphors were crystallized into monoclinic structure and well consistent with the JCPDS No. 34−0379. All these phosphors exhibit the characteristic emission transitions such as 4F9/2 → 6H15/2, 4F9/2 → 6H13/2 and 4F9/2 → 6H11/2 corresponding to blue (∼480 nm), yellow (∼572 nm) and red (∼663 nm) regions when excited at 350 nm near UV wavelength. Beyond 1.0 mol% concentration of Dy3+ ions, a luminescence quenching was noticed and it has been assigned to the energy transfer through dipole-dipole interactions at higher concentrations. Due to crystallization into nanophase, the SrAl2O4:Dy3+ phosphors exhibit novel and excellent luminescence properties at 350 nm excitation. The 1.0 mol% of Dy3+ -doped SrAl2O4 phosphor show a quantum yield of ∼9.52%. The experimental results suggest that the SrAl2O4:1.0 mol% Dy3+ phosphor could be the best choice to design white LEDs with bright and intense luminescence.

Novel Eu2+-activated thiogallate phosphors for white LED applications: structural and spectroscopic analysis.

Novel Eu2+-activated BaGa2SiS6 and Ba2Ga8SiS16 thiogallate phosphors were prepared by solid-state reaction route. The BaGa2SiS6:Eu2+ phosphor generated a green emission upon excitation at 405 nm, whereas the Ba2Ga8SiS16:xEu2+ phosphor could be tuned from cyan to green range with increasing Eu2+ concentration upon excitation at 365 nm. Additionally, the thermal luminescence properties of the thiogallate phosphors were investigated in the temperature range of 25 to 250 °C. A warm-white LED is fabricated using the combination of a 405 nm blue InGaN-based LED chip with the green-emitting BaGa2SiS6:0.01Eu2+ phosphor, and red-emitting Sr2Si5N8:Eu2+ commercial phosphor with the CRI value of ∼88 and the CCT of 4213 K.

Influence of substitution of Al-O for Si-N on improvement of photoluminescence properties and thermal stability of Ba2Si5N8:Eu2+ red emitting phosphors

Red emitting Ba2Si(5-x)AlxN(8-x)Ox:Eu2+ phosphors were successfully produced by high-temperature solid state reaction method and their luminescence properties were experimentally measured. The analysis of the experimental results suggests that the partial substitution of Al-O for Si-N in the host lattice improves the photoluminescence properties and the thermal stability of the produced phosphors. The phosphors exhibited a broad red emission band between 500 and 750 nm. A red shift of emission peak from 588 to 624 nm was recorded with the increase of Al-O content, attributed to the enhancement of stokes shift. The excitation spectrum of the produced phosphors ranged between 200 and 600 nm, covering the UV and the blue region, and suggesting these materials as potentially suitable for use as conversion phosphors for white LED applications in the field of solid state lighting.

Novel single-phase full-color emitting Ba9Lu2Si6O24:Ce3+/Mn2+/Tb3+ phosphors for white LED applications

Novel single-phase full-color-emitting Ba9Lu2Si6O24:Ce3+/Mn2+/Tb3+ phosphors were successfully synthesized by a high-temperature solid-state reaction method. Analysis of the X-ray diffractograms of the produced phosphors suggests that all the luminescence doping cations preferably occupy the Ba2+ sites in the host lattice. Li+ were used according to Ce3+ and Tb3+ concentration as a charge compensation regent. Under UV excitation, the single Ce3+-doped phosphor exhibits an intense blue emission band that peaks at 424 nm. In the co-doped phosphors, the experimental results suggest that an efficient energy transfer mechanism from Ce3+ to Tb3+ and Mn2+ results in the generation of a green emission in the Tb3+-doped phosphors and a red emission in the Mn2+-doped ones. The triple-doped phosphors, which contained specific concentrations of Ce3+, Mn2+, and Tb3+ ions, generated a tunable (in a wide range) white light which had good color rendering index values. Thermal behavior of the present phosphors was investigated which shows better characteristics. This result qualifies the produced powders as potential single-phase trichromatic white light-emitting phosphors.

(BaSr)2SiO4:Eu2+ nanorods with enhanced luminescence properties as green-emitting phosphors for white LED applications

To meet the requirements of warm white light-emitting diodes (WLEDs) with extreme thermal stability, high color rendering index and low color temperature, which is equivalent to natural sunlight, we need to develop novel phosphor materials that can efficiently absorb excitation energy from near-ultraviolet (NUV) LEDs and produce desired visible emissions. The Sr2+ and Eu2+ ions co-activated Ba2SiO4 ((BaSr)Si:Eu2+) green-emitting nanophopshors for NUV or blue excitation-based WLEDs are reported. After annealing at 1300 °C, the X-ray diffraction patterns established the pure orthorhombic phase of (BaSr)Si:Eu2+ nanophosphors. The evolution of (BaSr)Si:Eu2+ nanorods from the surface of the sub-micron sized (BaSr)Si:Eu2+ particles showed a tremendous effect on the luminescent properties by enhancing the transmittance of the (BaSr)Si:Eu2+ nanophosphor. The incorporation of Sr2+ ions along with Eu2+ ions into the Ba2+ sites, the emission intensity was increased, and also the quantum efficiency was enhanced from 47 to 59%. Upon excitation at 370 nm, the Ba2SiO4:Eu2+ phosphor exhibited a bluish-green emission while the yellowish-green emission was revealed by the (BaSr)Si:Eu2+ nanophosphor. The thermal stability of the (BaSr)Si:Eu2+ nanophosphor was verified at elevated temperatures and the activation energy for thermal quenching was found to be 0.38 eV. When the (BaSr)Si:Eu2+ nanophosphor was coated on a NUV LED chip, the enriched green emission was observed by increasing the input current from 100 to 250 mA. The (BaSr)Si:Eu2+ is expected to be a promising green-emitting phosphor material for the fabrication of NUV or blue excitation-based warm WLEDs for general illumination.

Synthesis and luminescence properties of NaLa(WO4)2:Eu3+ phosphors for white LED applications

Eu3+ activated NaLa(WO4)2 (NLW) red phosphors were synthesized via an ethylene glycol route at low temperature as 120 °C for solid state lighting applications. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), FT-IR, Raman, emission and excitation properties were studied for synthesized NLW phosphors. XRD analysis endorsed the formation of NaLa(WO4)2 with scheelite structure. For 9 mol% of Eu3+ concentration, the phosphor demonstrates an intensified narrow excitation peak at 394 nm indicating a strong absorption due to Eu3+ ion. The PL emission spectra of NaLa(WO4)2:0.09 Eu3+phosphors exhibited an intense peak at 615 nm (red) which agrees to 5D0→7F2 transition of Eu3+ at the excitation wavelength of 394 nm. The CIE colour coordinates of NaLa(WO4)2:0.09 Eu3+ red phosphor accord very well with the standard values of NTSC. The sterling luminescent properties of NaLa(WO4)2:0.09 Eu3+ phosphor executes it as a potential red phosphor upon near-UV LED excitation.

Tunable colorimetric performance of Al2O3-YAG:Ce3+ eutectic crystal by Ce3+ concentration

Ce-doped Al2O3-YAG eutectics with different percentage of Ce were successfully grown by the optical floating zone technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the structure. The results show that they have typical eutectic structure of interpenetrating sapphire and garnet phases with the tens of microns lamella spacing. The photoluminescence spectra of the eutectics showed that they have wide excitation band, and samples with 1.6mol% Ce-doped has the highest emission intensity. The eutectic-packaged LED has high luminous efficiency and its color can be modulated by changing Ce concentration. The results reveal that Ce-doped Al2O3-YAG eutectic is a promising phosphor for white LED applications.