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 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.     

Ca₂BO₃Cl:Ce³⁺,Tb³⁺:A novel tunable emitting phosphor for white light-emitting diode

<正>Ca₂BO₃Cl:Ce³⁺,Ca₂BO₃Cl:Tb³⁺,and Ca₂BO₃Cl:Ce³⁺,Tb³⁺ phosphors are synthesized by a high temperature solid-state reaction.The emission intensity of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl is influenced by the Ce³⁺ or Tb³⁺ doping content,and the optimum concentrations of Ce³⁺ and Tb³⁺ are 0.03 mol and 0.05 mol,respectively.The concentration quenching effect of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl occurs,and the concentration quenching mechanism is d-d interaction for either Ce³⁺ or Tb³⁺.The Ca₂BO₃Cl:Ce³⁺,Tb³⁺ can produce colour emission from blue to green by properly tuning the relative ratio between Ce³⁺ and Tb³⁺,and the emission intensity of Tb³⁺ in Ca₂BO₃Cl can be enhanced by the energy transfer from Ce³⁺ to Tb³⁺.The results indicate that Ca₂BO₃Cl:Ce³⁺,Tb³⁺ may be a promising double emission phosphor for UV-based white light emitting diodes.     

Ba3Tb(BO3)3 ∶Ce3+:一种白光LED用绿色荧光粉

采用高温固相法合成了Ba₃Tb(BO₃)₃和Ba₃Tb(BO₃)₃ ∶Ce³⁺两种绿色荧光粉,并研究了材料的发光性质.Ba₃Tb(BO₃)₃材料呈多峰发射,发射峰位于439,493,547,589和629 nm,分别对应Tb³⁺的⁵D关键词： 白光LED 3Tb(BO₃)₃')" href="#">Ba₃Tb(BO₃)₃ 3+')" href="#">Ce³⁺ 发光特性     

Violet-blue-shift of emission and enhanced luminescent properties of Ca3(PO4)2:Ce3+ phosphor induced by substitution of Gd3+ ions

Ca₃(PO₄)₂:1mol%Ce³⁺/xGd³⁺ (where x = 0.5, 1.0, 3.0 and 5.0 mol%) phosphors were synthesized by the conventional combustion synthesis method. The X-ray diffraction patterns showed their rhombohedral structure with space group of R3c. The optical properties including reflectance, excitation and emission were investigated. The band gaps of the phosphors were calculated from diffuse reflectance spectra data using the Kubelka–Munk function. The photoluminescence (PL) excitation spectra exhibited the broadband 4f–5d transition of Ce³⁺ ions centered at ~265 nm. The PL emission properties of the Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphors were studied as a function of the Gd³⁺ ion concentration. The Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphor had a wide emission band ranging from 320 to 400 nm, and peaking at 365 nm. This emission is ascribed to the transition from the higher 5d band to ²F_7/2, ²F_5/2 states of the Ce³⁺ ion. The 365 nm peak shifted to longer wavelengths with increasing concentration of the Gd³⁺ ion. The CIE chromaticity diagram of Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphor showed tunable emission colour from violet to violet-blue, suggesting that this phosphor can act as a source of violet-blue colour for application in information displays, phototherapy and photoluminescent liquid crystal displays.     

Potential tunable white-emitting phosphor LiSr4(BO3)3:Ce3+, Eu2+ for ultraviolet light-emitting diodes

A novel Ce³⁺/Eu²⁺ co-activated LiSr₄(BO₃)₃ phosphor has been synthesized by traditional solid-state reaction. The samples could display varied color emission from blue towards white and ultimately to yellow under the excitation of ultraviolet (UV) light with the appropriate adjustment of the relative proportion of Ce³⁺/Eu²⁺. The resonance-type energy transfer mechanism from Ce³⁺ to Eu²⁺ in LiSr₄(BO₃)₃:Ce³⁺, Eu²⁺ phosphors is dominant by electric dipole–dipole interaction, and the critical distance is calculated to be about 29.14 Å by the spectra overlap method. White light was observed from LiSr₄(BO₃)₃:mCe³⁺, nEu²⁺ phosphors with chromaticity coordinates (0.34, 0.30) upon 350 nm excitation. The LiSr₄(BO₃)₃:Ce³⁺, Eu²⁺ phosphor has potential applications as an UV radiation-converting phosphor for white light-emitting diodes.     

Luminescence properties of novel NaBa4(BO3)3:Ce, Eu phosphors

Novel Eu³⁺, Ce³⁺ activated NaBa₄(BO₃)₃ phosphors were synthesized by solid-state reactions. The excitation spectrum of NaBa₄(BO₃)₃:Ce³⁺ consists of an intense band peaking at 350 nm and a weak band in the higher energy side, and the emission spectrum exhibits a blue band with a maximum at about 420 nm. The Eu³⁺ emission in NaBa₄(BO₃)₃ consists of the transitions from ⁵D₀ to ⁷F_J, and the excitation spectrum consists of broad excitation band peaking at 270 nm and some intense narrow lines. The optimum doped concentration, the critical distance of the concentration quenching, and the fluorescence lifetime have also been investigated.     

Luminescence of Ce and Pr doped Sr2Mg(BO3)2 under VUV-UV and X-ray excitation

This report presents the luminescence properties of Ce³⁺ and Pr³⁺ activated Sr₂Mg(BO₃)₂ under VUV-UV and X-ray excitation. The five excitation bands of crystal field split 5d states are observed at about 46 729, 44 643, 41 667, 38 314 and 29 762 cm⁻¹ (i.e. 214, 224, 240, 261 and 336 nm) for Ce³⁺ in the host lattice. The doublet Ce³⁺ 5d→4f emission bands were found at about 25 840 and 24 096 cm⁻¹ (387 and 415 nm). The influence of doping concentration and temperature on the emission characteristics and the decay time of Ce³⁺ in Sr₂Mg(BO₃)₂ were investigated. For Pr³⁺ doped samples, the lowest 5d excitation band was observed at about 42017 cm⁻¹ (238 nm), a dominant band at around 35714 cm⁻¹ (280 nm) and two shoulder bands were seen in the emission spectra. The excitation and emission spectra of Ce³⁺ and Pr³⁺ were compared and discussed. The X-ray excited luminescence studies show that the light yields are ∼3200±230 and ∼1400±100 photons/MeV of absorbed X-ray energy for the samples Sr_1.86Ce_0.07Na_0.07Mg(BO₃)₂ and Sr_1.82Pr_0.09Na_0.09Mg(BO₃)₂ at RT, respectively.     

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.     

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).     

Spectroscopic characteristic of Ce3+ at two different sites in Ba3Lu(BO3)3 under ultraviolet excitation

A series of Ba₃Lu_{1 ? x} Ce _x (BO₃)₃ phosphors with different x value were prepared by a conventional high-temperature solid-state reaction method, and their spectroscopic characteristic were systematically investigated. The excitation and emission spectra indicate Ce³⁺ can occupy two different Lu lattice sites, and shows different luminescence properties. The spectroscopic characteristic of Ce(1) and Ce(2) which include Stokes shift and crystal field depression were investigated. The investigation indicates that Ba₃Lu(BO₃)₃: Ce³ phosphor can have potential application in white-light emitting diodes due to the near-ultraviolet excitation band and blue light emission of Ce(2) in Ba₃Lu(BO₃)₃.     

The concentration quenching and crystallographic sites of Eu2+ in Ca2BO3Cl

A yellow phosphor, Ca2BO3CI：Eu2＋, is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f65dl→4f7 transition of Eu2＋. Eu2＋ ions occupy two types of Ca2＋ sites in the Ca2BO3C1 lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu2＋ in Ca2BO3C1. The emission intensity of Eu2＋ in Ca2BO3C1 is influenced by the Eu2＋ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole-dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.     

Luminescence VUV spectroscopy of cerium-and europium-doped lithium borate crystals

The paper reports on a study of the luminescence of lithium borate crystals (Li₆Gd(BO₃)₃ doped by Eu³⁺ and Ce³⁺ ions, Li_5.7Mg_0.15Gd(BO₃)₃: Eu, and Li₆Eu(BO₃)₃) initiated by selective excitation by synchrotron radiation at excitation energies of 3.7–27 eV at 10 and 290 K. Efficient energy transfer between the rare-earth ions Gd³⁺ → Ce³⁺ and Gd³⁺ → Eu³⁺ was found to proceed by the resonance mechanism, as well as by electron-hole recombination. Fast decay kinetics of luminescence of the Ce³⁺ activator centers was studied under intracenter photoexcitation and excitation in the interband transition region. The mechanisms involved in luminescence excitation and radiative relaxation of electronic states of rare-earth ions are analyzed, and the energy transfer processes operating in these crystals are discussed.     

Luminescence enhancement by energy transfer from Ce ions in Ba1.6Ca0.4P2O7:Ce:Tb phosphor

The optical properties of Ba_1.6Ca_0.4P₂O₇ doped with Ce³⁺ and Tb³⁺ are investigated. Under excitation at 280 nm the emission spectrum of Ba_1.6Ca_0.4P₂O₇:Ce³⁺ consists of a peak at 370 nm and a shoulder at the longer wavelength side. The emission spectra of Ba_1.6Ca_0.4P₂O₇:Tb³⁺ shows the well-known emission lines due to ⁵D₄-⁷F_J transitions of Tb³⁺. The green emissions of Tb³⁺ ions are enhanced upon UV excitation through energy transfer from Ce³⁺ to Tb³⁺ ions. The efficiency of such an energy transfer is estimated based on spectroscopic data. The dependence of photoluminescence (PL) intensities of Ce³⁺ and Tb³⁺ emissions on Ce³⁺ or Tb³⁺ concentrations in the systems (Ba_1.6Ca_0.4P₂O₇:0.04Ce³⁺,xTb³⁺ and Ba_1.6Ca_0.4P₂O₇:xCe³⁺,0.04Tb³⁺) and the temperature dependence of PL emission spectra of Ba_1.6Ca_0.4P₂O₇:0.06Ce³⁺,0.04Tb³⁺ is also investigated.     

Photoluminescence and efficient energy transfer from Ce3+ to Tb3+ or Mn2+ in Ca9ZnLi(PO4)7 host

Structural and spectroscopic characterizations of the Ce³⁺/Tb³⁺(Mn²⁺) solely and Ce³⁺–Tb³⁺(Mn²⁺) doubly doped phosphate compound Ca₉ZnLi(PO₄)₇ with β-Ca₃(PO₄)₂ structure have been performed by powder X-ray diffraction and photoluminescence spectra measurements. The weak green emission from Tb³⁺ and red emission from Mn²⁺ are significantly enhanced by introduction of sensitizer Ce³⁺ ions due to an efficient resonant-type energy transfer from Ce³⁺ to activators Tb³⁺ or Mn²⁺. The energy transfer efficiency and the mechanism have been estimated based on spectroscopic data. Meanwhile, the critical distances for energy transfer between the Ce³⁺ and Tb³⁺ or Mn²⁺ ions are also calculated by the method of spectral overlapping.     

Preparation and Luminescence Characteristics of Ca3Y2（BO3）4：Eu^3＋ Phosphor

Ca3Y2 （BO3）4：Eu^3＋ phosphor is synthesized by high temperature solid-state reaction method, and the Iuminescence characteristics are investigated. The emission spectrum exhibits two strong red emissions at 613 and 621 nm corresponding to the electric dipole ^5 Do- ^7F2 transition of Eu^3＋ under 365 nm excitation, the reason is that Eu^3＋ substituting for Y^3＋ occupies the non-centrosymmetric position in the crystal structure of Ca3 Y2 （BO3）4. The excitation spectrum for 613 nm indicates that the phosphor can be effectively excited by ultraviolet （UV） （254 nm, 365nm and 400nm） and blue （470nm） light. The effect of Eu^3＋ concentration on the emission intensity of Ca3 Y2 （BO3）4 ：Eu^3＋ phosphor is measured, the result shows that the emission intensities increase with increasing Eu^3＋ concentration, then decrease. The CIE colour coordinates of Ca3Y2 （BO3）4：Eu^3＋ phosphor is （0.639, 0.357） at 15mol% Eu^3＋.     

Luminescence characteristics of Eu3+ activated borate phosphor for white light emitting diode

In this paper, the Sr₃Y₂ (BO₃)₄:Eu³⁺ phosphor was synthesized by high temperature solid-state reaction method and the luminescence characteristics were investigated. The emission spectrum exhibits one strong red emission at 613nm corresponding to the electric dipole ⁵D₀--⁷F₂ transition of Eu³⁺ under 365nm excitation, this is because Eu³⁺ substituted for Y³⁺ occupied the non-centrosymmetric position in the crystal structure of Sr₃Y₂ (BO₃)₄. The excitation spectrum indicates that the phosphor can be effectively excited by ultraviolet (254nm, 365nm and 400nm) and blue (470nm) light. The effect of Eu³⁺ concentration on the red emission of Sr₃Y₂ (BO₃)₄:Eu³⁺ was measured, the result shows that the emission intensities increase with increasing Eu³⁺ concentration, then decrease. The Commission Internationale del'Eclairage chromaticity (x, y) of Sr₃Y₂(BO₃)₄:Eu³⁺ phosphor is (0.640,0.355) at 15 mol% Eu³⁺.     

New red phosphors BaZr(BO3)2 and SrAl2B2O7 doped with Eu for PDP applications

Vacuum ultraviolet (VUV) excitation and photoluminescence (PL) characteristics of Eu³⁺ ion doped borate phosphors; BaZr(BO₃)₂:Eu³⁺ and SrAl₂B₂O₇:Eu³⁺ are studied. The excitation spectra show strong absorption in the VUV region with the absorption band edge at ca. 200 nm for BaZr(BO₃)₂:Eu³⁺ and 183 nm for SrAl₂B₂O₇:Eu³⁺, respectively, which ensures the efficient absorption of the Xe plasma emission lines. In BaZr(BO₃)₂:Eu³⁺, the charge transfer band of Eu³⁺ does not appear strongly in the excitation spectrum, which can be enhanced by co-doping Al³⁺ ion into the BaZr(BO₃)₂ lattices. The luminescence intensity of BaZr(BO₃)₂:Eu³⁺ is also increased by Al³⁺ incorporation into the lattices. The PL spectra show the strongest emission at 615 nm corresponding to the electric dipole ⁵D₀→⁷F₂ transition of Eu³⁺ in both BaZr(BO₃)₂ and SrAl₂B₂O₇, similar to that in YAl₃(BO₃)₄, which results in a good color purity for display applications.     

Luminescence properties and energy transfer in Ba2Y(BO3)2Cl:Ce3+,Tb3+ phosphors

Novel green-emitting Ba₂Y(BO₃)₂Cl:Ce³⁺,Tb³⁺ phosphors were synthesized by a solid-state method. X-ray diffraction and photoluminescence spectra were utilized to characterize the structures and luminescence properties of the as-synthesized phosphors, respectively. Ba₂Y(BO₃)₂Cl:Ce³⁺,Tb³⁺ phosphors exhibit blue and green emission bands under the excitation of near-ultraviolet light. An asymmetric blue emission originates from the Ce³⁺ ion, whereas the green emission originates from the Tb³⁺ ion. A spectral overlap is found between the emission band of the Ce³⁺ ion and the excitation band of the Tb³⁺ ion, which supports the occurrence of the energy transfer from the Ce³⁺ ion to the Tb³⁺ ion. Meanwhile, the energy transfer is thoroughly investigated by their photoluminescence decay behaviors. The energy-transfer efficiency from the Ce³⁺ ion to the Tb³⁺ ion is also calculated, and a possible mechanism is proposed.     

Quantum Effect on the Energy Levels of Eu2+ Doped K2Ca2(SO4)3 Nanoparticles

Quantum confinement effect on the energy levels of Eu²⁺ doped K₂Ca₂(SO₄)₃ nanoparticles has been observed. The broad photoluminescence (PL) emission band of Eu²⁺ doped K₂Ca₂(SO₄)₃ microcrystalline sample observed at ～436 nm is found to split into two narrow well resolved bands, located at 422 and 445 nm in the nanostructure form of this material. This has been attributed to the reduction in the crystal field strength of the nanomaterials, which results in widening the energy band gap and splitting the broad 4f⁶5d energy level of Eu²⁺. Energy band gap values of the micro and nanocrystalline K₂Ca₂(SO₄)₃ samples were also determined by measuring the UV–visible absorption spectra. These values are 3.34 and 3.44 eV for the micro and nanocrystalline samples, respectively. These remarkable results suggest that activators having wide emission bands might be subjected to weak crystal strength via nanostructure materials to modify their electronic transitions. This might prove a powerful technique for producing new-advanced materials for use in the fields of solid state lasers and optoelectronic devises.