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.     

Luminescence properties and energy transfer of Ba2Mg(PO4)2:Eu2+, Mn2+ phosphor synthesized by co-precipitation method

The Ba₂Mg(PO₄)₂:Eu²⁺, Mn²⁺ phosphor is synthesized by a co-precipitation method. Crystal phase, morphology, excitation and emission spectra of sample phosphors are analyzed by XRD, SEM and FL, respectively. The results indicate particles synthesized by a co-precipitation method have a smaller size in diameter than that synthesized by conventional solid-state reaction method. Emission spectra of BMP:Eu²⁺, Mn²⁺ phosphor show a broad blue and a broad yellow emission bands with two peaks at about 456 nm and 575 nm under 380 nm excitation. An overlap between Eu²⁺ emission band and Mn²⁺ excitation band proves the existence of energy transfer from Eu²⁺ to Mn²⁺. Emitting color of the BMP:Eu²⁺, Mn²⁺ phosphor could be tuned by adjusting relative contents of Eu²⁺ and Mn²⁺ owing to energy transfer formula. Therefore, BMP:Eu²⁺, Mn²⁺ may be considered as a potential candidate for phosphor for near-UV white LED.     

Synthesis and luminescence properties of Ca8NaGd(PO4)6F2: Eu2+, Mn2+ for white LEDs

A series of luminescent emission-tunable phosphors Ca₈NaGd(PO₄)₆F₂: Eu²⁺, Mn²⁺ have been prepared by a combustion-assisted synthesis method. The X-ray diffraction measurement results indicate that the crystal structure of the phosphor is a single phase of Ca₈NaGd(PO₄)₆F₂. The photoluminescence (PL) properties of Eu²⁺ and Mn²⁺-codoped Ca₈NaGd(PO₄)₆F₂ phosphors were also investigated. The phosphors can be efficiently excited by ultraviolet (UV) light and show a blue emission band at about 450 nm and a yellow emission band at about 574 nm, which originated from the Eu²⁺ ions and the Mn²⁺ ions, respectively. The efficient energy transfer from the Eu²⁺ ions to the Mn²⁺ ions was observed and its mechanism should be a resonant type via a nonradiative dipole–quadrupole interaction. A color-tunable emission in Ca₈NaGd(PO₄)₆F₂ phosphors can be realized by Eu²⁺ → Mn²⁺ energy transfer. Our results indicate that the developed phosphor may be used as a potential white emitting phosphor for UV based white LEDs.     

Photoluminescence properties of Sr3(PO4)2: Eu2+, Dy3+ double-emitting blue phosphor for white LEDs

Double-emitting blue phosphor Sr₃(PO₄)₂: Eu²⁺, Dy³⁺ was synthesized by solid state reaction under H₂ atmosphere. XRD exhibited the pure hexagonal phase of the prepared phosphor. The photoluminescence results showed that all samples had intense broad absorption band between 250 and 450 nm, which matched well with the near-UV (350–420 nm) emission band of InGaN-based chips. The emission spectrum of Sr₃(PO₄)₂: Eu²⁺, Dy³⁺ consisted of two broad bands, peaked at 485 nm and 410 nm, which originated from two luminescent centers, related to 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ in six-coordinated Sr(I) and ten-coordinated Sr(II) sites respectively. The intensity ratio of two emission bands could be easily tuned by adjusting Dy³⁺ co-doping content, which resulted in color-tunable luminescence in bluish green region to purplish blue region.     

Luminescent properties of Eu3+ 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.     

Investigation on the luminescence of RE3+ (RE = Ce,Tb, Eu and Tm) in KMGd(PO4)2 (M = Ca,Sr) phosphates

The VUV excited luminescent properties of Ce³⁺, Tb³⁺, Eu³⁺ and Tm³⁺ in the matrices of KMGd(PO₄)₂ (M = Ca, Sr) were investigated. The bands at about 165 nm and 155 nm in the VUV excitation spectra are attributed to host lattice absorptions of the two matrices. For Ce³⁺-doped samples, the Ce³⁺ 5d levels can be identified. As for Tb³⁺-doped samples, typical 4f–5d absorption bands in the region of 175–250 nm were observed. For Eu³⁺ and Tm³⁺-doped samples, the O²⁻–Eu³⁺ and O²–Tm³⁺ CTBs are observed to be at about 229 nm and 177 nm, respectively. From the standpoints of color purity and luminescent efficiency, KCaGd(PO₄)₂:Tb³⁺ is an attractive candidate of green light PDP phosphor.     

Combustion synthesis and luminescence properties of yellow-emitting phosphors Ca2BO3Cl:Eu2+

Yellow-emitting phosphor Ca₂BO₃Cl:Eu²⁺ was synthesized by a solution-combustion method. The phase structure and microstructure were determined by the X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis, respectively. The as-prepared Ca₂BO₃Cl:Eu²⁺ phosphor absorbed near ultraviolet and blue light of 320–500 nm, and showed an intense yellow emission band centered at 569 nm with the CIE coordinate of (0.453, 0.526). The lifetime of Eu²⁺ ions in Ca₂BO₃Cl:Eu²⁺ phosphor was measured, furthermore the temperature dependent luminescence property and mechanism were studied, which also testified that the present phosphor had a promising potential for white light-emitting diodes.     

A novel blue-emitting Ca2B5O9Br:Eu2+ phosphor prepared by a microwave calcination route

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 (270–420 nm) and a blue broad emission band of main peak at 452 nm under the strongest excitation of 411 nm. 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.     

Luminous properties of color tunable strontium thio-selenide phosphors for LEDs application

In this study, alkali earth thio-selenide phosphor, SrS_xSe_1 ? x:Eu²⁺_, was prepared using the conventional solid state reaction method. The synthesized phosphor displayed a broad excitation band that was suitable for blue or near UV LED applications and emitted light at various wavelengths (563–605 nm) with different chemical compositions. Like the case of other alkali phosphors, Zn²⁺ substitution for Sr²⁺ greatly enhanced the emission of this thio-selenide phosphor. The LED fabricated with the synthesized phosphor produced white light using a blue LED with a CIE-1931 coordinate, T_c and R_a of (0.3199, 0.3107), 6577 K and 51.6, respectively.     

Photoluminescence of CaAlSiN3:Eu2+-based fine red-emitting phosphors synthesized by carbothermal reduction and nitridation method

In this research, we have presented the synthesis and characterization of the various Ca_1−xEu_xAl_0.76Si_1.18N₃ (x = 0.01 ∼ 0.1) red-emitting phosphors, which were successfully prepared by carbothermal reduction and nitridation (CTRN) method without the strict needs of high pressure. Here, raw materials were CaCO₃, AlN, Si₃N₄, Eu₂O₃, and C. In particular, C was considered as efficient and robust reducing agent. The influences of reaction temperature, holding time, C content, and Eu²⁺ concentration were investigated in the crystal phase compositions and photoluminescence properties of the as-prepared phosphors. Importantly, CaAlSiN₃:Eu²⁺-based red phosphors with interesting properties were obtained with reaction temperature at 1600 °C for 4 h by atmospheric N₂–10%H₂ pressure, and the C/O ratio of 1.5:1, respectively. The emission peak positions of as-prepared phosphors were red-shifted from 607 nm to 654 nm with Eu²⁺ concentration from 1 mol% to 10 mol%. Meanwhile the highest luminescence intensity was achieved with 2 mol% of Eu²⁺ concentration, which showed high external quantum efficiency up to 71%. Combining the phosphor blend of green-emitting β-sialon:Eu²⁺, yellow-emitting Ca-α-sialon:Eu²⁺, and red-emitting Ca_0.98Eu_0.02Al_0.76Si_1.18N₃ with a blue LED (light emitting diodes), warm white LED can be generated, yielding the color rendering index (Ra) of 93 at correlated color temperature (CCT) of 3295 K. These results indicate that CaAlSiN₃:Eu²⁺-based red-emitting phosphors prepared by facile CTRN are highly promising candidates for warm white LEDs.     

Synthesis and two-color emission properties of BaGd2(MoO4)4:Eu3+,Er3+,Yb3+ phosphors

Eu³⁺, Er³⁺ and Yb³⁺ co-doped BaGd₂(MoO₄)₄ two-color emission phosphor was synthesized by the high temperature solid-state method. The structure of the sample was characterized by XRD, and its luminescence properties were investigated in detail. Under the excitation of 395 nm ultraviolet light, the BaGd₂(MoO₄)₄:Eu³⁺,Er³⁺,Yb³⁺ phosphor emitted an intense red light at 595 and 614 nm, which can be attributed to ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions of Eu³⁺, respectively. The phosphor will also show bright green light under 980 nm infrared light excitation. The green emission peaks centred at 529 and 552 nm, were attributed to ⁴H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺, respectively. It indicated that the two-color emission can be achieved from the same BaGd₂(MoO₄)₄:Eu³⁺,Er³⁺,Yb³⁺ host system based on the different pumping source, 395 nm UV light and 980 nm infrared light, respectively. The obtained results showed that this kind of phosphor may be potential in the field of multi-color fluorescence imaging and anti-counterfeiting.     

Time-dependent PSL studies on CsBrCl:Eu2+: a promising image screen phosphor

The time-resolved PSL studies of CsBr_1−xCl_x:Eu²⁺ system has been studied for different europium concentrations. An efficient PSL material for use in image plate should have very short PSL emission lifetime. PSL emission lifetime for stimulation at 650 and 630 nm (F(Br⁻)- and F(Cl⁻)-centers) for CsBrCl:Eu²⁺ is determined to be 0.69 μs. The lifetime of BaFBr:Eu²⁺, the commercially available image screen phosphor is 0.8 μs. The present observation support the use of CsBrCl:Eu²⁺ as an efficient X-ray image screen phosphor.     

Photoluminescence properties of green-emitting Eu2+-activated Ba3Si6O12N2 oxynitride phosphor for white LED applications

Eu²⁺-activated Ba₃Si₆O₁₂N₂ green-emitting phosphors were synthesized by a solid-state reaction method. X-ray diffraction patterns showed that the synthesized phosphor sintered at 1200 °C for 12 h was a Ba₃Si₆O₁₂N₂ pure phase. The synthesized phosphors were excited in UV to blue light. The emission spectra showed a broad green emission band when excited with a light at 465 nm. The highest emission intensity was observed at a Eu²⁺ concentration of 0.25 mol and the NH₄Cl concentration of the optimized flux was found to be 9 wt.%. The obtained green-emitting Ba₃Si₆O₁₂N₂:Eu²⁺ phosphors could be applied to white LED applications.     

Luminescent properties of Eu3+ activated MLa2(MoO4)4 based (M = Ba,Sr and Ca) novel red-emitting phosphors

Eu³⁺-activated novel red phosphors, MLa₂(MoO₄)₄ (M = Ba, Sr and Ca) were synthesized by the conventional solid state method. The excitation and emission spectra indicate that these phosphors can be effectively excited by UV (395 nm) and blue (466 nm) light, and exhibit a satisfactory red performance at 614 nm. Upon excitation with a 466 nm light, our synthesized phosphors have stronger emission intensity than the sulfide red phosphors used in white LEDs. Due to high emission intensity and a good excitation profile, the Eu³⁺-doped CaLa₂(MoO₄)₄ phosphor may be a promising candidate in solid-state lighting applications.     

A novel single-phased white light emitting phosphor with single Eu2+ doped whitlockite structure

Exploring novel efficient single-phased full spectrum phosphor with individual activator doping for white light emitting diodes is highly significative and benefit for scientific activities. Herein, by designing and modifying the β-Ca₃(PO₄)₂-type structure, the Ca₁₉MgNa₂(PO₄)₁₄: Eu²⁺ (CMNP) phosphor was proposed as a single-phased full spectrum white phosphor. The phase purity and clear crystal structure were then determined by employing the Rietveld refinement and energy dispersive X-ray spectroscopy. PLE and PL spectra indicated CMNP: xEu²⁺ (0.1% ≤ x ≤ 1.0%) phosphors could be well fitted with 365 nm LED chip and exhibited a full spectrum emission band covering all visible lights of 400–750 nm belonging to the 5d?4f transitions of Eu²⁺. Further, the selective occupation of Eu²⁺ ions in different cation sites and luminescence kinetics depending on the Eu²⁺ dopants were characterized by theoretical calculation, Rietveld refinement results and decay curves. Finally, the WLED device fabricated by (near)-UV WLED chip and CMNP: 0.75 %Eu²⁺ phosphor could present excellent color temperature (6643 K) and CIE coordinate (0.308, 0.346). The current work manifests that Ca₁₉MgNa₂(PO₄)₁₄: Eu²⁺ had excellent luminescent property, which could be used in optical applications.     

Visible quantum cutting through downconversion in Eu3+-doped K2GdZr(PO4)3 phosphor

K₂Gd_1?xZr(PO₄)₃:Eu_x³⁺ (0.02 ≤ x ≤ 0.1, x is in mol.%) were prepared by solid-state reaction method and their photoluminescence properties were investigated in ultra-violet (UV) and vacuum ultra-violet (VUV) region. The phenomenon of visible quantum cutting through downconversion was observed for the Gd³⁺–Eu³⁺ couple in this Eu³⁺-doped K₂GdZr(PO₄)₃ system. Visible quantum cutting, the emission of two visible light photons per absorbed VUV photon, occurred upon the 186 nm excitation of Gd³⁺ at the ⁶G_J level via two-step energy transfer from Gd³⁺ to Eu³⁺ by cross-relaxation and sequential transfer of the remaining excitation energy. The results revealed that the efficiency of the energy transfer process from Gd³⁺ to Eu³⁺ in the Eu³⁺-doped K₂GdZr(PO₄)₃ system could reach to 155% and K₂GdZr(PO₄)₃:Eu³⁺ was effective quantum cutting material.     

A novel red phosphor Na2Ca4Mg2Si4O15:Eu3+ for plasma display panels

A novel red emitting phosphor, Eu³⁺-doped Na₂Ca₄Mg₂Si₄O₁₅, was prepared by the solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the formation of Na₂Ca₄Mg₂Si₄O₁₅:Eu³⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated a narrow size-distribution of about 300 nm for the particles with spherical shape. Upon excitation with vacuum ultraviolet (VUV) and near UV light, the phosphor showed strong red-emission lines at around 611 and 617 nm, respectively, corresponding to the forced electric dipole ⁵D₀ → ⁷F₂ transition of Eu³⁺, and the highest PL intensity at 617 nm was found at a content of about 8 mol% Eu³⁺. The optical properties study suggests that it is a potential candidate for plasma display panels (PDPs) application.     

Abnormal blue-shift of Eu2+-activated calcium zirconium phosphates CaZr4(PO4)6

The electronic structure of CaZr₄(PO₄)₆ was calculated using the CASTEP code and the band gap for CaZr₄(PO₄)₆ can reach up to 4.30 eV. Ca_1−xEu_xZr₄(PO₄)₆ (0.01 ⩽ x ⩽ 1) samples were prepared by a high temperature solid-state reaction method. XRD analysis shows that Eu²⁺ ion can be totally incorporated into CaZr₄(PO₄)₆ forming complete solid solutions with trigonal lattice. Ca_1−xEu_xZr₄(PO₄)₆ (0.01 ⩽ x ⩽ 1) shows typical broad band emission in wavelength range from 400 to 650 nm for both under ultraviolet (UV) light and X-ray excitation, originating from the 4f⁶5d¹ → 4f⁷5d⁰ transition of Eu²⁺ ions. With increasing Eu²⁺ concentration, there is abnormal blue-shift of the emission peaks for Ca_1−xEu_xZr₄(PO₄)₆ due to the decreasing crystal field strength and Stokes shift. With increasing temperature in CaZr₄(PO₄)₆: Eu²⁺, its emission bands show the anomalous blue-shift with decreasing intensity. The overall scintillation efficiency of Ca_0.9Eu_0.1Zr₄(PO₄)₆ is 1.7 times of that of Bi₄Ge₃O₁₂ (BGO) powder under the same conditions. In addition, its predominant decay time is about 50 ns at room temperature. The potential application of Eu²⁺-doped CaZr₄(PO₄)₆ has been pointed out.     

Optical studies on X and γ irradiated vacuum grown CsBrI:Eu2+ crystals

CsBr_0.9I_0.1:Eu²⁺ crystals were grown by Bridgman technique. Optical absorption spectrum of the unirradiated CsBr_0.9I_0.1:Eu²⁺ crystals show absorption bands at 270 nm and 340 nm. Irradiated CsBr_0.9I_0.1:Eu²⁺ shows single F band for F(Br⁻) and F(I⁻) centers at 730 nm. Conversion of Eu²⁺ to Eu³⁺ after irradiation is confirmed by optical absorption technique. Sharp and single Photoluminescence (PL) emission band is observed at 440 nm for CsBr_0.9I_0.1:Eu²⁺ crystals. Photostimulated Luminescence (PSL) emission band observed for CsBr_0.9I_0.1:Eu²⁺ crystals at 442 nm due to excitation at 730 nm shows that the F centers are photostimulable. PSL emission intensity increases linearly with irradiation dose up to 2.5 Krad.     

Variation of the photoluminescence and vacuum ultraviolet excitation characteristics of BaZr(BO3)2:Eu3+ by the incorporation of Al3+, La3+, or Y3+ into the lattice

The photoluminescence (PL) and vacuum ultraviolet (VUV) excitation properties are studied for the BaZr(BO₃)₂:Eu³⁺ phosphor with incorporating the Al³⁺, La³⁺, or Y³⁺ ion into the lattice. The excitation spectrum shows an absorption band in the VUV region with the band-edge at 200 nm and a very weak charge transfer band of Eu³⁺ at about 226 nm. The luminescence spectrum shows a strong emission at 615 nm (⁵D₀ → ⁷F₂ transition) and weak emission at 594 nm (⁵D₀ → ⁷F₁ transition) in BaZr(BO₃)₂:Eu³⁺, with a good red color purity. The PL intensity is increased by incorporating Al³⁺ into the BaZr(BO₃)₂ lattice. The PL intensity has also increased by incorporating La³⁺ into the lattice, however, the red color purity has deteriorated because of the increased centrosymmetric nature of the site. With the incorporation of Y³⁺ into the BaZr(BO₃)₂ lattice, the PL characteristics of the Eu³⁺ activator resembles that in the YBO₃ lattices. The intensity of the red PL for the Eu³⁺ activator is the highest with good color purity for BaZr(BO₃)₂:Eu³⁺ incorporated with both Al³⁺ (10%) and La³⁺ (0.5%).