Luminescent properties of red-emitting LiSr4B3O(9−3x/2)Nx:Eu2+ phosphor for white-LEDs

An Eu²⁺-activated oxynitride LiSr_(4?y)B₃O_(9?3x/2)N_x:yEu²⁺ red-emitting phosphor was synthesized by solid-state reactions. The synthesized phosphor crystallized in a cubic system with space group Ia–3d. The LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphors exhibited a broad red emission band with a peak at 610 nm and a full width at half maximum of 106 nm under 410 nm excitation, which is ascribed to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The optimal doped nitrogen concentration was observed to be x=0.75. The average decay times of two different emission centers were estimated to be 568 and 489 ns in the LiSr_3.99B₃O_8.25N_0.5:0.01Eu²⁺ phosphors, respectively. Concentration quenching of Eu²⁺ ions occurred at y=0.07, and the critical distance was determined as 17.86 Å. The non-radiative transitions via dipole–dipole interactions resulted in the concentration quenching of Eu²⁺-site emission centers in the LiSr₄B₃O₉ host. These results indicate LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphor is promising for application in white near-UV LEDs.     

On the Luminescence of Ce<Superscript>3+</Superscript>, Eu<Superscript>3+</Superscript>, and Tb<Superscript>3+</Superscript> in Novel Borate LiSr<Subscript>4</Subscript>(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>

This paper reports on the photoluminescence (PL) and time-resolved properties of Ce³⁺, Eu³⁺, and Tb³⁺ in novel LiSr₄(BO₃)₃ powder phosphors. Ce³⁺ shows an emission band peaking at 420 nm under 350-nm UV excitation. Energy transfer from Ce³⁺ to Mn²⁺ takes place in the co-doped samples. Eu³⁺ shows red emission under near UV excitation. LiSr₄(BO₃)₃:Eu³⁺ phosphor could be a suitable candidate for phosphor-converted solid state lighting. The luminescence lifetime is 2.13 ms for Eu³⁺ in LiSr₄(BO₃)₃:0.001Eu³⁺. As Eu³⁺ concentration increasing, the decay curves deviate from exponential behavior. Tb³⁺ shows the strongest ⁵D₄→⁷ F₅ emission line at 540 nm. Decay curves of ⁵D₄→⁷ F₅ and ⁵D₃→⁷ F₅ emission with different Tb³⁺ concentrations were also measured. Cross-relaxation process is discussed based on the decay curves.     

Ca8Mg(SiO4)4Cl2:Ce3+, Tb3+: A potential single-phased phosphor for white-light-emitting diodes

A single-phased white-light-emitting phosphor Ca₈Mg(SiO₄)₄Cl₂:Ce³⁺, Tb³⁺ (CMSC:Ce³⁺, Tb³⁺) is synthesized by a high temperature solid-state reaction method, and its photoluminescence properties are investigated. The obtained phosphor exhibits a strong excitation band between 250 and 410 nm, matching well with the dominant emission band of a UV light-emitting-diode (LED) chip. Energy transfer from Ce³⁺ to Tb³⁺ ions has been investigated and demonstrated to be a resonant type via a dipole–dipole mechanism. The energy transfer efficiency as well as the critical distance is also estimated. Furthermore, the phosphors can generate light from yellow-green through white and eventually to blue by properly tuning the relative ratio of Ce³⁺ to Tb³⁺ ions grounded on the principle of energy transfer. The results show that this phosphor has potential applications as a single-phased phosphor for UV white-light LEDs.     

Synthesis and luminescence properties of green phosphors Ca6Sr4(Si2O7)3Cl2:Eu2+ for white light emitting diodes

Divalent europium-activated chlorosilicate Ca₆Sr₄(Si₂O₇)₃Cl₂:Eu²⁺ phosphors were synthesized by a conventional solid-state reaction under reductive atmosphere. These phosphors can be efficiently excited by UV–visible light from 320 to 420 nm, which matches that of a near UV-emitting InGaN chip. Under the 360 nm excitation, Ca₆Sr_3.97(Si₂O₇)₃Cl₂:0.03Eu²⁺ phosphor shows a strong and broad emission centering at 515 nm, which is attributed to the 5d→4f transition of Eu²⁺ ion. The mechanism of concentration quenching was determined to be the dipole–dipole interaction and the critical energy-transfer distance of Eu²⁺ was calculated as 3.31 nm. The CIE chromaticity coordinates of Ca₆Sr_3.96(Si₂O₇)₃Cl₂:0.03Eu²⁺ phosphor are (0.127, 0.770) according to the emission spectrum. It can be expected that Ca₆Sr₄(Si₂O₇)₃Cl₂:Eu²⁺ phosphor is a promising candidate as the green component for near-ultraviolet InGaN-based white LED.     

Ca2BO3Cl:Ce,Eu: A potential tunable yellow-white-blue-emitting phosphors for white light-emitting diodes

Polycrystalline Ca₂BO₃Cl:Ce³⁺,Eu²⁺ phosphors were synthesized by a solid-state reaction and which could display tunable color emission from blue to yellow under an ultraviolet (UV) source by adjusting the ratio of Ce³⁺ and Eu²⁺ appropriately. The mechanism of resonance-type energy transfer from Ce³⁺ to Eu²⁺ was established to be electric dipole-dipole natured, and the critical distance was estimated to be 31 Å based on the spectral overlap and concentration quenching model. A white light was obtained from Ca₂BO₃Cl:0.06Ce³⁺,0.01Eu²⁺ phosphor with chromaticity coordinates (x=0.31, y=0.29) and relative color temperature of 7330 K upon excitation with 360 nm, which is potentially a good candidate as an UV-convertible phosphor for white light-emitting diodes (LEDs).     

Photoluminescence characterization of a novel red-emitting phosphor In2(MoO4)3:Eu3+ for white light emitting diodes

The red-emitting phosphor In₂(MoO₄)₃:Eu³⁺ with cubic crystal structure was synthesized by a conventional solid-state reaction technique and its photoluminescence properties were investigated. The prepared phosphor can be efficiently excited by ultraviolet (395 nm) and blue (466 nm) light. The emission spectra of the phosphor manifest intensive red-emitting lines at 612 nm due to the electric dipole ⁵D₀→⁷F₂ transitions of Eu³⁺. The chromaticity coordinates of x=0.63, y=0.35 (λ_ex=395 nm) and x=0.60, y=0.38 (λ_ex=466 nm) are close to the standard of National Television Standard Committee values (NTSC) values. The concentration quenching of In₂(MoO₄)₃:Eu³⁺ is 40 mol% and the concentration self-quenching mechanism under 466 nm excitation was the dd intereaction. As a result of the strong emission intensity and good excitation, the phosphor In₂(MoO₄)₃:Eu³⁺ is regarded as a promising red-emitting conversion material for white LEDs.     

Concentration quenching of Eu2+ in a thermal-stable yellow phosphor Ca2BO3Cl:Eu2+ for LED application

A piece-shaped phosphor Ca₂BO₃Cl: Eu²⁺ was synthesized by solid-state reaction method. This phosphor exhibited wide absorption in ultra-violet and visible range, and bright yellow emission band centering at 570 nm. The concentration quenching mechanism was verified to be a dipole–dipole interaction, and its critical transfer distance was about 17 Å by both calculated crystal structural method and experimental spectral method. This phosphor has a good thermal stability with a quenching temperature (T_1/2) of 200 °C. Yellow and white LEDs were fabricated with this phosphor and near UV chips, and the yellow LED has a high color purity of 97.0% and promising current tolerant property, while the white LED shows a luminous efficiency of 11.68 lm/W.     

Synthesis and photoluminescence properties of YVO4:Eu3+, Al3+ phosphor

The Y_0.95?xAl_xVO₄:5%Eu³⁺ (0≤x≤0.1) phosphors were successfully synthesized by solid state reaction at 900 °C for 6 h, and their luminescence properties were investigated under UV and VUV excitation. Monitoring at 619 nm, a strong broad absorption was enhanced by co-doping of Al³⁺ into the YVO₄:Eu³⁺ lattices at 256 nm under UV excitation. The VUV excitation spectra also showed the enhanced excitation bands at about 156 and 200 nm. Under 254 or 147 nm excitation, it was found that Y_0.95?xAl_xVO₄:Eu³⁺(0≤x≤0.1) phosphors showed strong red emission at about 619 nm corresponding to the electric dipole ⁵D₀^–7F₂ transition of Eu³⁺. The improvement of luminescence intensity of YVO₄:Eu³⁺ was also observed after partial substituting Y³⁺ by Al³⁺ and the optimal luminescence intensity appeared with incorporation of 2.5 mol% Al³⁺.     

Luminescent properties of Mg3Ca3(PO4)4: Eu2+ blue-emitting phosphor for white light emitting diodes

A blue-emitting phosphor, Eu²⁺-activated Mg₃Ca₃(PO₄)₄ phosphor was synthesized by conventional solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the phase formation. Photoluminescence (PL) results showed that Mg₃Ca₃(PO₄)₄: Eu²⁺ could be efficiently excited by UV–visible light from 250 to 430 nm, which matched well with the emission wavelengths of near-UV and UV LED chips. The effects of the doped-Eu²⁺ concentration in Mg₃Ca₃(PO₄)₄: Eu²⁺ on the PL were also investigated. The result reveals that Mg₃Ca₃(PO₄)₄: Eu²⁺ is a potential blue-emitting phosphor for white LEDs.     

Synthesis and luminescence properties of Eu, Ce and Tb-activated Sr3La2(BO3)4 under UV excitation

The spectroscopic properties in UV-excitable range for the phosphors of Sr₃La₂(BO₃)₄:RE³⁺ (RE³⁺=Eu³⁺, Ce³⁺, Tb³⁺) were investigated. The phosphors were synthesized by conventional solid-state reactions. The photoluminescence (PL) spectra and commission international de I'Eclairage (CIE) coordinates of Sr₃La₂(BO₃)₄:RE³⁺ were investigated. The f-d transitions of Eu³⁺, Ce³⁺ and Tb³⁺ in the host lattices are assumed and corroborated. The PL and PL excitation (PLE) spectra indicate that the main emission wavelength of Sr₃La₂(BO₃)₄:Eu³⁺ is 611 nm, and Sr₃La₂(BO₃)₄:Ce³⁺ shows dominating emission peak at 425 nm, while Sr₃La₂(BO₃)₄:Tb³⁺ displays green emission at 487, 542, 582 and 620 nm. These phosphors were prepared by simple solid-state reaction at 1000 °C. There are lower reactive temperature and more convenient than commercial phosphors. The Sr₃La₂(BO₃)₄:Tb³⁺ applied to cold cathode fluorescent lamp was found to emit green light and have a major peak wavelength at around 542 nm. These phosphors may provide a new kind of luminescent materials under ultraviolet excitation.     

Photoluminescence properties of a new Eu2+-activated CaLaGa3S7 yellowish-green phosphor for white LED applications

A thiogallate chalcogenide phosphor CaLaGa₃S₇:Eu²⁺ was synthesized by a solid-state reaction at 950 °C in a H₂S atmosphere. The photoluminescence excitation,emission spectra, concentration quenching, fluorescence lifetime, and thermal quenching process of the phosphor were investigated in detail. It was found that the synthesized phosphor emitted intense and broadband yellowish-green light with a peak at 554 nm. Thus, the proposed phosphor is suitable for the development of blue or near UV LED. The critical dopant concentration of Eu²⁺ (R_c=15 Å) per unit formula was found to be 0.15 mol. At room temperature, the fluorescence lifetime of Eu²⁺ in CaLaGa₃S₇ was found to be 0.216 μs. The activation energy for thermal quenching was 0.29 eV. The chromaticity coordinates of our phosphor is very close in color to Y₃Al₅O₁₂:Ce³⁺. Therefore, CaLaGa₃S₇:Eu²⁺ can be a good alternative as a yellowish-green phosphor and can be used for white light generation in phosphor-converted LEDs.     

Double emitting phosphor NaSr4(BO3)3:Ce, Tb for near-UV light-emitting diodes

Blue and green double emitting phosphor, Ce³⁺ and Tb³⁺ co-doped NaSr₄(BO₃)₃, was synthesized in a weak reducing atmosphere by a conventional high temperature solid-state reaction technique. For comparison, Ce³⁺ or Tb³⁺ singly doped NaSr₄(BO₃)₃ was also prepared. The emission and excitation spectra of all samples have been investigated. NaSr₄(BO₃)₃:Tb³⁺ excitation includes a strong absorption at about 240 nm and some weak sharp lines in near-ultraviolet (n-UV) spectral region. The excitation of Ce³⁺ and Tb³⁺ co-doped NaSr₄(BO₃)₃ shows a strong broad band absorption in the n-UV region from the contribution of Ce³⁺, which makes it suitable for excitation by a n-UV LED chip. The emission of NaSr₄(BO₃)₃:Ce³⁺,Tb³⁺ consists of a blue emission band from Ce³⁺ and a green emission from Tb³⁺ under the excitation of n-UV light. Energy transfer between Ce³⁺ and Tb³⁺ is also discussed, and the relative intensity of blue emission and green emission could be tuned by adjusting the concentration of Ce³⁺ and Tb³⁺. The phosphor NaSr₄(BO₃)₃:Ce³⁺,Tb³⁺ could be considered as a double emission phosphor for n-UV excited white light-emitting diodes.     

Synthesis and luminescence properties of a broad-band red phosphor Ca3Si2O7:Eu2+ for warm white light-emitting diodes

Single-phase broad-band red-emitting Ca₃Si₂O₇:Eu²⁺ phosphors, with photoluminescence features that qualify them as candidates for white light-emitting diodes applications, were successfully synthesized via a modified solid-state reaction method that employed H₃BO₃ as a flux. The phosphors produced have an intense broad red emission band, with a peak at 603 nm, a full width at half maximum of 110 nm, and color coordinates of (0.550, 0.438). Concentration quenching occurred at 0.01 mol Eu²⁺. The discussion of the results shows that Eu²⁺ ions should be accommodated at the Ca-sites of the lattice, dipole–dipole interactions should predominantly govern the energy transfer mechanism among them, and the critical distance between them is ～31 Å.     

Photoluminescence properties of Ca9Lu(PO4)7:Ce3+, Mn2+ prepared by conventional solid-state reaction

A new red-emitting phosphor Ca₉Lu(PO₄)₇:Ce³⁺, Mn²⁺ has been synthesized by solid-state reaction, and its luminescence properties have been investigated. The broad red emission peaked at 645 nm of Mn²⁺ is greatly enhanced by the sensitizer Ce³⁺ due to efficient energy transfer from Ce³⁺ to Mn²⁺. The energy transfer was demonstrated to belong to a resonant type via a dipole–quadrupole mechanism. The critical distance for Ce³⁺→Mn²⁺ energy transfer was calculated to be 15.04 Å by concentration quenching method. Preliminary results indicate that the phosphor might be a promising red phosphor for UV-based white LEDs.     

Photoluminescence properties of Eu2+–Mn2+ codoped Ca-α-SiAlON phosphors

Eu²⁺–Mn²⁺ codoped Ca-α-SiAlON phosphors, Ca_0.736?ySi_9.6Al_2.4O_0.8N_15.2:0.064 Eu²⁺, yMn²⁺, were firstly synthesized by the high temperature solid state reaction method. The effects of doped Eu²⁺ and Eu²⁺–Mn²⁺ concentrations on the photoluminescence properties of the as-prepared phosphors were investigated systematically. Powder X-ray diffraction shows that pure Ca-α-SiAlON phase is synthesized after sintering at 1700 °C for 2 h under 0.5 MPa N₂ atmosphere. The excitation spectra of Eu²⁺-doped Ca-α-SiAlON phosphors are characterized by two dominant bands centered at 286 nm and 395 nm, respectively. The photoluminescent spectrum of Eu²⁺-doped Ca-α-SiAlON phosphor exhibits an intense emission band centered at 580 nm due to the allowed 4f ⁶5d→4f ⁷ transition of Eu²⁺, showing that the phosphor is a good candidate for creating white light when coupled to a blue LED chip. The intensities of both excitation and emission spectra monotonously decrease with the increment of codoped Mn²⁺ content (i.e. y value), indicating that energy transfer between Eu²⁺ and Mn²⁺ is inefficient in the case of Eu²⁺–Mn²⁺ codoped Ca-α-SiAlON phosphors.     

Emission-tunable phosphors Ca9MgM′ (PO4)7: Eu2+,Mn2+ (M′=Li,Na, K) for white light-emitting diodes

A series of single-composition phosphors Ca₉MgM′(PO₄)₇:xEu²⁺, yMn²⁺ (CMM′ P:Eu²⁺, Mn²⁺; M′=Li, Na, K; 0.003≤x≤0.03; 0 ≤y≤0.1) were synthesized by solid state reactions. Upon excitation at 337 nm, phosphors Ca₉MgM′ (PO₄)₇: Eu²⁺ exhibit strong blue emissions centered at 417 (Ca₉MgLi(PO₄)₇:Eu²⁺), 457 (Ca₉MgNa(PO₄)₇:Eu²⁺), and 453 (Ca₉MgK(PO₄)₇:Eu²⁺) nm respectively, which correspond to the 4f⁶5d¹→4f⁷ transitions of Eu²⁺ ions, Through an effective resonance-type energy transfer, CMM′P:Eu²⁺,Mn²⁺ phosphors exhibit a series of colors by adjusting the concentration of Mn²⁺. The result indicates that CMM′P:Eu²⁺,Mn²⁺ can be potentially used as a UV excited phosphor for white light-emitting diodes (LEDs).     

A potential red emitting K4Ca(PO4)2: Eu3+ phosphor for white light emitting diodes

Europium (III) ions doped red phosphors K₄Ca(PO₄)₂ were prepared first time by high temperature solid state reaction method. The prepared phosphors structure was examined by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analyses. The thermal properties of the synthesized phosphor were investigated by differential scanning calorimetry (DSC) analysis. Photoluminescence (PL) spectra of K₄Ca(PO₄)₂:Eu³⁺ phosphors have shown strong red emission at 618 nm (⁵D₀→⁷F₂) with near UV an excitation wavelength of λ_exc=394 nm (⁷F₀→⁵L₆). In addition, the decay curves and CIE color coordinate measurements are also carried out. Hence, emission and excitation characterization of synthesized phosphors shows that the phosphors may be a promising red component for the application in the white light emitting diodes (WLEDs).     

Luminescent properties and energy transfer of double-emitting NaSrPO4:Eu2+,Tb3+ phosphor for near-UV white LEDs

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 430 nm, which was in agreement with the near-UV chip (350–420 nm), and it exhibited two dominating emission bands at 445 and 545 nm, corresponding to the allowed 4f⁶5d¹→4f⁷(⁸S_7/2) 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.     

Phase dependent photoluminescence and energy transfer in Ca2P2O7: Eu2+, Mn2+ phosphors for white LEDs

α- and β-Ca₂P₂O₇: Eu²⁺, Mn²⁺ phosphors were prepared by solid-state reaction. Phase transition from tetragonal (β-phase) to monoclinic (α-phase) is performed. A strong orange emission of Mn²⁺ is observed in both α-and β-Ca₂P₂O₇: Eu²⁺, Mn²⁺ upon near ultraviolet (UV) excitation through energy transfer from Eu²⁺ to Mn²⁺. The transfer efficiencies for various Mn²⁺ concentrations are estimated based on lifetime measurements of the fluorescence of Eu²⁺ in the two phases. The photoluminescence excitation spectra of α-Ca₂P₂O₇: Eu²⁺, Mn²⁺ can cover 400 nm of the near-UV range, denoting its potential use as a phosphor with intense orange component for white light emitting diodes (LEDs).     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Bi(PO4)3 phosphors

A series of orange reddish emitting phosphors Eu³⁺-doped Sr₃Bi(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence (PL) properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr₃Bi(PO₄)₃:Eu³⁺ phosphors invariably exhibit five peaks assigned to the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions of Eu³⁺ and have dominating emission peak at 612 nm under 392 nm excitation. The luminescence intensity was enhanced with increasing Eu³⁺ content and the emission reached the maximum intensity at x=0.05 in Sr₃Bi(PO₄)₃:xEu³⁺. The energy transfer behavior in the phosphors was discussed. The Commission Internationale de lEclairage (CIE) chromaticity coordinates, the quantum efficiencies, and the decay curves of the entitled phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Bi(PO₄)₃ phosphors are promising orange reddish-emitting phosphors pumped by near-UV light.