Luminescent properties of Eu-activated nanophosphors Ca3Y0.8Gd0.2(VO4)2.4(PO4)0.6: Eu for light-emitting diodes

Eu³⁺-doped Ca₃Y_0.8Gd_0.2(VO₄)_2.4(PO₄)_0.6 nanophosphors have been prepared by modified solid-state reaction. X-ray powder diffraction, transmission electron microscopy (TEM), photoluminescence excitation and emission spectra were used to characterize the resulting samples. X-ray powder diffraction (XRD) analysis confirmed the formation of YVO₄. Photoluminescence (PL) results showed that the phosphor could be efficiently excited by UV-visible light from 350 to 550 nm, exhibiting bright orange-red emission(excited by 397) and red emission(excited by 467), which has potential application as a phosphor for UV and blue GaN-based light-emitting diodes (LEDs). TEM images show that the grain size of Ca₃Y_0.45Eu_0.35Gd_0.2(VO₄)_2.4(PO₄)_0.6 is about 39 nm, which is in full agreement with the theoretical calculation data from the XRD patterns.     

A novel blue emitting phosphor NaBa0.98Eu0.02PO4 and the improvement of its luminescence properties

A novel blue-emitting phosphor NaBa_0.98Eu_0.02PO₄ was synthesized by conventional solid state reaction, and it exhibits efficient blue emission under near-ultraviolet (n-UV) excitation. The emission spectrum shows a single band centered at about 440 nm, which corresponds to the 4f⁶5d¹-4f⁷ transition of Eu²⁺. The excitation spectrum is a broad band in the wavelength range between 200 and 450 nm, which can match the emission of white light emitting diodes (LEDs) by the method of n-UV conversion. The Ca²⁺, Sr²⁺ and Mg²⁺ were co-doped into NaBa_0.98Eu_0.02PO₄ respectively. Special attention was paid to the sample co-doped with Ca²⁺ that could possess a higher luminous efficacy than the analogs co-doped with Sr²⁺ and Mg²⁺. With the co-doping of Ca²⁺, the enhanced intensity of the excitation and emission band appears. The optimum co-doping concentration of Ca²⁺ is 7 mol.%. The emission intensity of NaBa_0.91Ca_0.07Eu_0.02PO₄ phosphoris about 1.68 times than that of NaBa_0.98Eu_0.02PO₄ phosphor. The as-prepared phosphors are the potential blue phosphors for application in white LEDs.     

Novel blue-emitting phosphor NaMg4(PO4)3:Eu, Ce with energy transfer

A blue-emitting phosphor of NaMg₄(PO₄)₃:Eu²⁺, Ce³⁺ was prepared by a combustion-assisted synthesis method. The phase formation was confirmed by X-ray powder diffraction measurement. Photoluminescence excitation spectrum measurements show that the phosphor can be excited by near UV light from 230 to 400 nm and presents a dominant luminescence band centered at 424 nm due to the 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions at room temperature. Effective energy transfer occurs in Ce³⁺/Eu²⁺ co-doped NaMg₄(PO₄)₃ due to large spectral overlap between the emission of Ce³⁺ and excitation of Eu²⁺. Co-doping of Ce³⁺ enhances the emission intensity of Eu²⁺ greatly by transferring its excitation energy to Eu²⁺, and Ce³⁺ plays a role as a sensitizer. Ce³⁺-Eu²⁺ co-doped NaMg₄(PO₄)₃ powders can possibly be applied as blue phosphors in the fields of lighting and display.     

Photoluminescence of Tb and Mn activated Ca8MgGd(PO4)7 under vacuum ultraviolet excitation

Novel Tb³⁺ and Mn²⁺ activated Ca₈MgGd(PO₄)₇ phosphors were synthesized by solid-state reaction and their photoluminescence properties in vacuum ultraviolet region were investigated for the first time. It can be observed from the excitation spectra that the host-related absorption band is located around 170 nm, and it overlaps the O²⁻ → Tb³⁺ charge transfer band of Ca₈MgGd(PO₄)₇:Tb³⁺ around 161 nm and the 3d⁵ → 3d⁴4s transition band of Ca₈MgGd(PO₄)₇:Mn²⁺ near 200 nm. The 4f-4f 5d spin-allowed and spin-forbidden transitions of Tb³⁺ are verified to be located at 170-250 and 257-271 nm, respectively. Upon 147 nm excitation, the dominant emission peak intensity of the Ca₈MgGd_0.1(PO₄)₇:0.9Tb³⁺ phosphor is about 2.7 times stronger than that of the commercial Zn₂SiO₄:Mn²⁺ green phosphor, and the brightness of the former with a short decay time of 2.5 ms is about 98% of the latter’s. The Ca₈MgGd(PO₄):Mn²⁺ phosphor excited at 147 nm exhibits a deep red emission around 650 nm, which could be attributed to the ⁴T₁ → ⁶A₁ transition of Mn²⁺, with the CIE index (0.679, 0.321). In a word, the results above indicate that both Tb³⁺ and Mn²⁺ activated Ca₈MgGd(PO₄)₇ phosphors could be promising for PDP or Hg-free lamp applications.     

Luminescence and microstructures of Eu-doped in triple phosphate Ca8MgR(PO4)7 (R = La, Gd, Y) with whitlockite structure

Eu³⁺-doped triple phosphate Ca₈MgR(PO₄)₇ (R = La, Gd, Y) was synthesized by the general high temperature solid-state reaction. This phosphor was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and emission spectra. XRD and FT-IR analysis indicated that Ca₈MgR(PO₄)₇ (R = La, Gd, Y) crystallized in single-phase component with whitlockite-like structure (space group R3c) of β-Ca₃(PO₄)₂. Under the excitation of UV light, the phosphors show bright red emission assigned to the transition (⁵D₀ → ⁷F₂) at 612 nm. The crystallographic sites of Eu³⁺ ions in Ca₈MgR(PO₄)₇ (R = La, Gd, Y) host were discussed on the base of site-selective excitation and emission spectra, luminescence decay and its host crystal structure.     

Photoluminescence properties of emission-tunable Ca9Y(PO4)7: Tm,Dy phosphor for white light emitting diodes

A white-emitting Ca₉Y(PO₄)₇: Tm³⁺, Dy³⁺ phosphor has been successfully prepared by conventional high-temperature solid-state reaction. X-ray diffraction (XRD) and fluorescence spectrophotometer were used to characterize the as-synthesized phosphors. The excitation and emission spectra show that all the Tm³⁺ and Dy³⁺ co-doped Ca₉Y(PO₄)₇ samples can be effectively excited by UV light and then emit blue and yellow light simultaneously. Furthermore, the emission and color coordinate of as-obtained samples pumped by 365 nm are able to be adjusted around white light by varying the doping concentrations of Tm³⁺ and Dy³⁺. So, the as-fabricated single-composition Ca₉Y(PO₄)₇: Tm³⁺, Dy³⁺ phosphor will have a promising application in the area of white light emitting diodes.     

White-emitting phosphors Ca6La2Na2(PO4)6F2:Dy and luminescence enhancement through Ce → Dy energy transfer

Ce³⁺ and Dy³⁺ activated fluoro-apatite Ca₆La₂Na₂(PO₄)₆F₂ with chemical formulas Ca₆La_2−xLn_xNa₂(PO₄)₆F₂ (Ln = Ce³⁺, Dy³⁺) were prepared by a solid state reaction technique at high temperature. The vacuum-ultraviolet (VUV) and ultraviolet (UV) spectroscopic properties are investigated. The results indicate that Ce³⁺ ions show the lowest 5d excitation band at ∼305 nm and a broad emission band centered at ∼345 nm. Dy³⁺ ions exhibit intense absorption at VUV and UV range. White-emitting under 172 nm excitation is obtained based on two dominant emissions from Dy³⁺ ions centered at 480 and 577 nm. In addition, the energy transfer from Ce³⁺ to Dy³⁺ in the co-doped samples are observed and discussed.     

Synthesis and photoluminescence properties of Yb doped Ba5(PO4)3Cl phosphor for white light-emitting diodes

Yb²⁺ ion doped Ba₅(PO₄)₃Cl phosphor was synthesized by solid state reaction. Four distinct absorption bands were observed in the Ultraviolet (UV) light region due to the electronic transitions of Yb²⁺ ion from ¹S₀ ground state to ²F_5/2(t_2g), ²F_5/2(e_g), ²F_7/2(t_2g), and ²F_7/2(e_g) excited states. The main emission wavelength of the phosphor was around 630 nm. The optimized Yb²⁺ ion concentration was 0.2 mol% (λ_exc. = 400 nm). The calculated critical distance was about 8.729 Å and the concentration quenching was observed above 0.2 mol% due to the electric dipole–dipole interaction.     

Luminescent properties of Eu doped α-Gd2(MoO4)3 phosphor for white light emitting diodes

A novel red emitting phosphor α-Gd₂(MoO₄)₃:Eu³⁺ was developed for white light emitting diodes (LEDs). The phosphor was prepared by solid-state reaction. The effects of the flux content and the activator concentration on the crystal structure, morphology and luminescent properties were investigated by using XRD, SEM, and fluorescent spectra. These results showed that this phosphor can be effectively excited by ultraviolet (UV) (395 nm) and blue (465 nm) light, matching the output wavelengths of ultraviolet or blue LED chips. The α-Gd₂ (MoO₄)₃ phosphor may be a better candidate for solid state lighting application.     

Improvement of alkali corrosion resistance of mullite ceramics at high temperature by depositing Ca0.3Mg0.2Zr2(PO4)3 coating

Ca_0.3Mg_0.2Zr₂(PO₄)₃ coating was deposited on the mullite ceramic to improve its alkali corrosion resistance at high temperatures, using sol–gel method and dip-coating technique. The phase composition and microstructure of the coating were characterized by X-ray diffraction and scanning electron microscopy (SEM). Results show that homogeneous, dense and single-phase Ca_0.3Mg_0.2Zr₂(PO₄)₃ coating was successfully deposited on mullite ceramics. SEM microstructural examination revealed the excellent bonding between Ca_0.3Mg_0.2Zr₂(PO₄)₃ coating and mullite ceramics. The effectiveness of the prepared coating to improve the alkali corrosion resistance of mullite ceramics was assessed through the measurements of mass loss and flexural strength degradation after 96 h and longer exposure time at alkali corrosion condition at 1000 °C. A significant enhancement of the alkali corrosion resistance for Ca_0.3Mg_0.2Zr₂(PO₄)₃-coated mullite samples was observed. Therefore, the effectiveness of the Ca_0.3Mg_0.2Zr₂(PO₄)₃ material as protection coating for mullite ceramic is confirmed.     

Synthesis and photoluminescence properties of a cyan-emitting phosphor Ca3(PO4)2:Eu2+ for white light-emitting diodes

In this paper, a cyan-emitting phosphor Ca₃(PO₄)₂:Eu²⁺ (TCP:Eu²⁺) was synthesized and evaluated as a candidate for white light emitting diodes (WLEDs). This phosphor shows strong and broad absorption in 250–450 nm region, but the emission spectrum is prominent at around 480 nm. The emission intensity of the TCP:Eu²⁺ was found to be 60% and 82% of that of the commercial BaMgAl₁₀O₁₇:Eu²⁺ (BAM) under excitation at 340 nm and 370 nm, respectively. Upon excitation at 370 nm, the absolute internal and external quantum efficiencies of the Ca₃(PO₄)₂:1.5%Eu²⁺ are 60% and 42%, respectively. Moreover, a white LED lamp was fabricated by coating TCP:Eu²⁺ with a blue-emitting BAM and a red-emitting CaAlSiN₃:Eu²⁺ on a near-ultraviolet (375 nm) LED chip, driven by a 350 mA forward bias current, and it produces an intense white light with a color rendering index of 75.     

Luminescence properties of Eu2+-activated Sr5(PO4)2(SiO4) for green-emitting phosphor

A green-emitting phosphor of Eu²⁺-activated Sr₅(PO₄)₂(SiO₄) was synthesized by the conventional solid-state reaction. It was characterized by photoluminescence excitation and emission spectra, and lifetimes. In Sr₅(PO₄)₂(SiO₄):Eu²⁺, there are at least two distinguishable Eu²⁺ sites, which result in one broad emission situating at about 495 nm and 560 nm. The phosphor can be efficiently excited in the wavelength range of 250–440 nm where the near UV (～ 395 nm) Ga(In)N LED is well matched. The dependence of luminescence intensities on temperature was investigated. With the increasing of temperature, the luminescence of the phosphor shows good thermal stability and stable color chromaticity. The luminescence characteristics indicate that this phosphor has a potential application as a white light emitting diode phosphor.     

Near UV-based LED fabricated with Ba5SiO4(F,Cl)6:Eu as blue- and green-emitting phosphor

A series of halosilicate phosphor, Ba₅SiO₄(F,Cl)₆:Eu²⁺, were synthesized by a solid state reaction. Excited by 370-nm light, Ba₅SiO₄Cl₆:Eu²⁺ exhibits a broad emission band peaking at 440 nm. Partial substitution of Cl⁻ with F⁻ in the host lattice leads to red-shift in the emission band with centering wavelength from 440 nm to 503 nm. The possible mechanism for the luminescence change was discussed based on the XRD patterns. Blue and green LEDs were fabricated by combination of a 370 nm-emitting near UV chip and the optimal Ba₅SiO₄Cl₆:Eu²⁺ and Ba₅SiO₄(F₃Cl₃):Eu²⁺, respectively. This series of phosphors is considered as a promising blue and green component used in fabrication of near UV-based white LEDs.     

Near-ultraviolet excitable Ca4Y6(SiO4)6O: Ce,Tb white phosphors for light-emitting diodes

The present investigation aims to demonstrate the potentiality of Tb³⁺ and Ce³⁺ co-doped Ca₄Y₆(SiO₄)₆O phosphors. By incorporation of Ce³⁺ into Ca₄Y₆(SiO₄)₆O: Tb³⁺, the excitation band was extended from short-ultraviolet to near-ultraviolet region. The energy transfer from Ce³⁺ to Tb³⁺ in Ca₄Y₆(SiO₄)₆O host was investigated and demonstrated to be a resonant type via a dipole–dipole mechanism with the critical distance of 10.2 Å. When excited by 352 nm, Ca₄Y₆(SiO₄)₆O: Ce³⁺, Tb³⁺ exhibited a brighter and broader violet-blue emission (421 nm) from the Ce³⁺ and an intense green emission (542 nm) from the Tb³⁺. Combining the two emissions whose intensities were adjusted by changing the doping levels of the co-activator, an optimized white light with chromaticity coordinates of (0.278, 0.353) is generated in Ca₄Y₆(SiO₄)₆O: 2% Ce³⁺, 8% Tb³⁺, and this phosphor could be potentially used in near-ultraviolet light-emitting diodes.     

Crystal structure and luminescent properties of europium-activated Ca10? x M x (PO4)6F2 (M = Pb, Mg) prepared via precipitation from aqueous solutions

Phase-pure polycrystalline fluorapatites with the general formula Ca_10−x M _x (PO₄)₆F₂:Eu³⁺(M = Pb, Mg) have been prepared by precipitation from aqueous solutions, and the effects of the Pb²⁺ and Mg²⁺ ions, differing markedly in ionic radius, on the structure, morphology, and luminescence spectra of the fluorapatites have been investigated. The Pb²⁺ and Mg²⁺ contents are shown to influence the Eu³⁺ distribution over inequivalent sites in the crystal structure of Ca_10−x M _x (PO₄)₆F₂. Original Russian Text ? N.V. Babayevskaya, Yu.N. Savvin, A.V. Tolmachev, 2007, published in Neorganicheskie Materialy, 2007, Vol. 43, No. 8, pp. 976–980.     

A potential Eu-activated Ca10K(PO4)7 red phosphor for white light-emitting diodes

New red Ca₁₀K(PO₄)₇:Eu³⁺, K⁺ phosphors were synthesized by solid state reaction and their photoluminescence properties as well as those by co-doping Mo⁶⁺ under near ultraviolet excitation were investigated. From the excitation spectra monitored at 611 nm, it can be seen that the strongest excitation peak is situated at 393 nm, well matching with the emission wavelength of near-ultraviolet chips for white LEDs. Upon 393 nm excitation, the brightness of Ca₉K(PO₄)₇:0.5Eu³⁺, 0.5 K⁺ with the optimal Eu³⁺-doping concentration is about 2.3 times stronger than that of the commercial red Y₂O₃:Eu³⁺ phosphor. The introducing of Mo⁶⁺, which results in a possible variety for the excited energy level of the host, can enhance the brightness of Eu³⁺ to be maximized by about 15%. The CIE chromaticity coordinates of Ca₉K(PO₄)₇:0.5Eu³⁺, 0.5 K⁺ are calculated to (0.654, 0.345), which are close to the (0.67, 0.33) standard of the National Television System Committee. All the above results indicate Eu³⁺-activated Ca₁₀K(PO₄)₇ is a potential candidate for white LEDs.     

A new yellowish green luminescent material SrMoO4:Tb

A novel yellowish green phosphor tervalent terbium (Tb³⁺) doped strontium molybdate (SrMoO₄) was synthesized by conventional solid-state reaction method and its crystal structure and luminescent properties are investigated in this paper. The X-ray diffraction patterns (XRD) showed that the phosphor sintered at 750 °C for 3 h was a pure SrMoO₄ phase. The excitation spectrum consisted of two bands and the two excitation peaks located at 375 nm and 488 nm respectively. The emission spectrum was composed of four narrow bands, in which the strongest emission was located at 548 nm. The particle size analysis indicated that the median particle size D₅₀ = 2.89 μm and range of particle size distribution was narrow. These results showed that the SrMoO₄:Tb³⁺ phosphor was a promising yellowish green phosphor for ultraviolet light emitting diode (UVLED) and blue LED based white LED. The appropriate concentration of Tb³⁺ was 5 mol% for the highest emission intensity at 548 nm. Natrium ion (Na⁺) was found to be a promising charge compensator for SrMoO₄:Tb³⁺ phosphor.     

Luminescence properties of Ca4Y6(SiO4)6O:RE (RE = Eu, Tb, Dy, Sm and Tm) under vacuum ultraviolet excitation

The vacuum ultraviolet excited luminescent properties of Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺ and Tm³⁺ in the matrices of Ca₄Y₆(SiO₄)₆O were investigated. The bands at about 173 nm in the vacuum ultraviolet excited spectra were attributed to host lattice absorption of the matrix Ca₄Y₆(SiO₄)₆O. For Eu³⁺-doped samples, the O²⁻ → Eu³⁺ CTB was identified at 258 nm. Typical 4f-5d absorption bands in the region of 195-300 nm were observed in Tb³⁺-doped samples. For Dy³⁺-doped and Sm³⁺-doped samples, the broad excitation bands consisted of host absorptions, CTB and f-d transition. For Tm³⁺-doped samples, the O²⁻ → Tm³⁺ CTB was located at 191 nm. About the color purity and emission intensity, Ca₄Y₆(SiO₄)₆O:Tb³⁺ is an attractive candidate of green light PDP phosphor, and Ca₄Y₆(SiO₄)₆O:Dy³⁺ has potential application in the field of mercury-free lamps.     

Visible quantum cutting via downconversion in a novel green-emitting K2Gd(WO4)(PO4):Tb phosphor

A novel phosphor K₂Gd(WO₄)(PO₄):Tb was prepared via a solid-state reaction. The crystal structure of K₂Gd(WO₄)(PO₄) as a new host matrix for luminescence was defined to be the orthorhombic system with space group Ibca (73). Visible quantum cutting under Tb³⁺ 4f⁸–4f⁷5d¹ excitation and host excitation in K₂Gd(WO₄)(PO₄):Tb³⁺ via a downconversion was identified. In order to rationalize the quantum cutting effect, the proper mechanism was proposed. According to calculations, the quantum efficiency was up to 183.2% and 176.4% under excitation at 235 nm and 150 nm, respectively. When compared with Zn₂SiO₄:Mn²⁺ (P1-G1S), KGWP:0.5Tb³⁺ is slightly less bright over 450–650 nm but has a shorter decay time.     

A novel blue emitting phosphor NaBa<Subscript>0.98</Subscript>Eu<Subscript>0.02</Subscript>PO<Subscript>4</Subscript> and the improvement of its luminescence properties

A novel blue-emitting phosphor NaBa_0.98Eu_0.02PO₄ was synthesized by conventional solid state reaction, and it exhibits efficient blue emission under near-ultraviolet (n-UV) excitation. The emission spectrum shows a single band centered at about 440 nm, which corresponds to the 4f⁶5d¹-4f⁷ transition of Eu²⁺. The excitation spectrum is a broad band in the wavelength range between 200 and 450 nm, which can match the emission of white light emitting diodes (LEDs) by the method of n-UV conversion. The Ca²⁺, Sr²⁺ and Mg²⁺ were co-doped into NaBa_0.98Eu_0.02PO₄ respectively. Special attention was paid to the sample co-doped with Ca²⁺ that could possess a higher luminous efficacy than the analogs co-doped with Sr²⁺ and Mg²⁺. With the co-doping of Ca²⁺, the enhanced intensity of the excitation and emission band appears. The optimum co-doping concentration of Ca²⁺ is 7 mol.%. The emission intensity of NaBa_0.91Ca_0.07Eu_0.02PO₄ phosphoris about 1.68 times than that of NaBa_0.98Eu_0.02PO₄ phosphor. The as-prepared phosphors are the potential blue phosphors for application in white LEDs.