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.     

Effects of excitation wavelength and Y3+ content on luminescent properties of YMO4:Dy3+ (M = V,P) phosphors induced by ultraviolet excitation

Y_0.99VO₄:0.01Dy³⁺, Y_0.99PO₄:0.01Dy³⁺ and Y_xVO₄:0.01Dy³⁺ phosphors were synthesized by chemical co-precipitation method. All the samples were characterized by X-ray powder diffraction (XRD) and photoluminescence spectroscopy. XRD results show that the samples only have single tetragonal structure and the crystallinity of Y_0.99VO₄:0.01Dy³⁺ phosphor is higher than that of Y_0.99PO₄:0.01Dy³⁺ phosphor when the heat treatment process is same. Photoluminescence excitation spectra results show that the Y_0.99VO₄:0.01Dy³⁺ and Y_0.99PO₄:0.01Dy³⁺ phosphors can be efficiently excited by ultraviolet light from 250 nm to 380 nm, the former have a wide Dy³⁺–O^2? charge transfer band ranging from 260 nm to 350 nm including a peak at 310 nm, the latter have four peaks at 294 nm, 326 nm, 352 nm and 365 nm. Emission spectra of all the samples exhibit a strong blue emission (483 nm) and another strong yellow emission (574 nm). Moreover, the yellow-to-blue emission intensity ratio and color temperature of emission of Dy³⁺ are strongly related to excitation wavelength in Y_0.99PO₄:0.01Dy³⁺ phosphor, but it is almost not in Y_0.99VO₄:0.01Dy³⁺ phosphor. For Y_xVO₄:0.01Dy³⁺ (x = 0.94, 0.97, 0.99, 1.01, 1.03) phosphors, with increasing value of x, the body color of phosphor changes from yellow to white and the strongest peak in excitation spectra shifts a little to shorter wavelength. It is detrimental to luminous intensity when Y³⁺ content deviate stoichiometric ratio, but the influence of Y³⁺ on the color temperature of emission of YVO₄:Dy³⁺ phosphor is slight.     

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 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.     

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.     

Sr3Bi(PO4)3:Eu2+, Mn2+: Single-phase and color-tunable phosphors for white-light LEDs

Sr₃Bi(PO₄)₃:Eu²⁺, Sr₃Bi(PO₄)₃:Mn²⁺, and Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ phosphors were synthesized by solid state reaction. The structure and luminescent characteristics were investigated by X-ray powder diffraction and fluorescent spectrophotometer. All samples have the structural type of eulytine. The excitation and emission spectra of Sr₃Bi(PO₄)₃:0.01Eu²⁺ sample show characteristic bands of Eu²⁺ ions. Also, the excitation and emission spectra of Sr₃Bi(PO₄)₃:0.06Mn²⁺ sample show characteristic bands of Mn²⁺ ions. The emission color of Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ sample could be tuned through tuning the co-dopant concentration of Mn²⁺ ions. The decay times for the Eu²⁺ ions decrease with the increase of Mn²⁺ dopant concentration, but the energy transfer efficiency increases with the increase of Mn²⁺ dopant concentration. On the basis of the luminescent spectra and fluorescence decay curves, we confirm that the energy transfer process from the Eu²⁺ to Mn²⁺ ions takes place in the co-doped Sr₃Bi(PO₄)₃ phosphor. Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ sample shows the good thermostability. The emission intensity of the sample at 400 K is about 60% of the value at 300 K. These results show Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ phosphors could be anticipated for UV-pumped white-light-emitting diodes.     

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.     

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.     

Optical characteristics and charge transfer band excitation of Dy3+ doped Y2O3 phosphor

Dy³⁺ ion-doped Y₂O₃ phosphors have been synthesized and characterized for structure and optical properties. Structural characterization reveals that the samples are well crystalline. The crystallinity and particle size increases as the sample is post annealed, while optical quenching entities are reduced due to which a significant enhancement in fluorescence is observed. The phosphor is efficiently excited by ultraviolet light and emits intense blue (486 nm), yellow (573 nm), red (666 nm), and near infrared (764 nm, 823 nm) light. The emission is also observed even if charge transfer band (CTB) is excited, via energy transfer from CTB to 4f levels of Dy³⁺ ion. The intensity of yellow transition band varies with a variation in concentration of Dy³⁺ ion as well as with excitation wavelength, while the intensity of other transitions remains unaffected. Thus a variation in yellow to blue color (Y/B) gives an opportunity for the development of color tunable phosphor.     

Luminescence properties of Na3SrB5O10:Dy3+ plate-like microstructures for solid state lighting applications

A series of novel plate-like microstructure Na₃SrB₅O₁₀ doped with various Dy³⁺ ions concentration have been synthesized for the first time by solid-state reaction (SSR) method. X-ray diffraction (XRD) results demonstrated that the prepared Na₃SrB₅O₁₀:Dy³⁺ phosphors are single-phase pentaborates with triclinic structure. The plate-like morphology of the phosphor is examined by Field emission scanning electron microscopy (FE-SEM). The existence of both BO₃ and BO₄ groups in Na₃SrB₅O₁₀:Dy³⁺ phosphors are identified by Fourier transform infrared (FT-IR) spectroscopy. Upon excitation at 385 nm, the PL spectra mainly comprising of two broad bands: one is a blue light emission (∼486 nm) and another is a yellow light emission (∼581 nm), originating from the transitions of ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 in 4f⁹ configuration of Dy³⁺ ions, respectively and the optimized dopant concentration is determined to be 3 at.%. Interestingly, the yellow-to-blue (Y/B) emission integrated intensity ratio is close to unity (0.99) for 3 at.% Dy³⁺ ions, suggesting that the phosphors are favor for white illumination. Moreover, the calculated Commission International de l’Eclairage (CIE) chromaticity coordinates of Na₃SrB₅O₁₀:Dy³⁺ phosphors shows the values lie in white light region and the estimated CCT values are located in cool/day white light region.     

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.     

VUV–UV luminescence of Ce3+, Tb3+, Eu3+, and Dy3+ doped GdOCl

The vacuum ultraviolet spectroscopic properties of GdOCl:Re³⁺ (Re³⁺ = Ce³⁺, Tb³⁺, Eu³⁺, and Dy³⁺) are investigated in detail for the first time. The host absorption band is determined to be around 179 nm, and the f–d transition bands as well as the charge transfer bands are assigned. Upon 179 nm excitation, Re³⁺ (Re³⁺ = Ce³⁺, Tb³⁺, Eu³⁺, Dy³⁺) ions shown their characteristic emissions. Energy transfers from Gd³⁺ to Re³⁺ ion were observed. A broad band ranging from 350 to 400 nm corresponding to the d–f transition of Ce³⁺ is observed. Eu³⁺ has typical red emission with the strongest peak at 620 nm; Tb³⁺ shows characteristic transition of ⁵D_3,4 → ⁷F_j, and its spin-forbidden and spin-allowed f–d transitions in VUV region are calculated with Dorenbos’ equations, these calculated values agree well with the experimental results. Dy³⁺ presents yellow emission (⁴F_9/2 → ⁶H_13/2) with the strongest peak at 573 nm.     

Synthesis and efficient blue-emitting of Eu2+-activated borate fluoride BaAlBO3F2

Eu²⁺-doped borate fluoride BaAlBO₃F₂ was synthesized by the conventional high temperature solid state reaction. The crystal phase formations were confirmed by X-ray powder diffraction (XRD) measurements and the structure refinement. The photoluminescence (PL) excitation and emission spectra, and the decay curves were investigated. Eu²⁺-doped BaAlBO₃F₂ phosphor can be efficiently excited by near-UV light and presents narrow blue luminescence band centered at 450 nm. The maximum absolute quantum efficiency (QE) of BaAlBO₃F₂:0.05Eu²⁺ phosphor was measured to be 76% excited at 398 nm light at 300 K. The thermal stability of the blue luminescence was evaluated by the luminescence decays as a function of temperature. The phosphor shows an excellent thermal stability with high thermal activation-energy on temperature quenching effects because of the rigid crystal lattices.     

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.     

Synthesis,characterization and luminescence of Sr3Al2O6 phosphor with trivalent rare earth dopant

The luminescent properties of Sr₃Al₂O₆ doped and co-doped with the rare earths (Ln³⁺ = Eu³⁺, Dy³⁺, Eu³⁺ and Dy³⁺) have been studied. The material was synthesized by reflux method and fired up to 900 °C for 16 h. The X-ray diffraction pattern confirms that the synthesized material consists of Sr₃Al₂O₆ as main phase. The photoluminescence study gives a clear evidence of europium stabilizing in trivalent form and surprisingly with no presence of europium in the divalent state. The addition of Dy³⁺ as co-dopant in the Sr₃Al₂O₆:Eu³⁺ matrix shows the quenching effect in the photoluminescence (PL) spectra. The photoluminescence intensity of Eu³⁺ falls gradually on increasing the concentration of the co-dopant in the range from 0.1 mole% to 2.0 mole%. The significantly intense thermoluminescence (TL) glow peak was obtained for Sr₃Al₂O₆:Eu³⁺, Dy³⁺ (1% and 0.1%) at around 194 °C when irradiated with 10 kGy dose from Sr-90 β source.     

Synthesis of new green-emitting KBa1−xScSi3O9:Eu2+x phosphors for white LEDs

New green-emitting KBa_1−xScSi₃O₉:Eu²⁺_x phosphors for white LEDs were synthesized by a conventional solid-state reaction method. The obtained KBa_1−xScSi₃O₉:Eu²⁺_x phosphors show the strong broad optical absorption band from UV to blue light region and exhibit broad green emission with a peak at 521 nm under excitation at 405 nm due to the allowed 4f⁶5d¹−4f⁷ transition of Eu²⁺. Optimization of Eu²⁺ concentration resulted in the highest green emission peak intensity was obtained at the composition of KBa_0.94ScSi₃O₉:Eu²⁺_0.06, and the relative emission intensity of this phosphor was 32% of that of a commercial YAG:Ce³⁺ phosphor.     

Eu3+ activated novel alkaline earth metal gallium oxide phosphors: Sr(2.92−x)Ca(x)Ga2O6:Eu3+0.08 for light emitting diodes

Present study deals with Eu³⁺ activated novel alkaline earth metal (Sr and Ca) gallium oxide phosphors, Sr_(2.92?x)Ca_(x)Ga₂O₆:Eu³⁺_0.08 (x = 0 to 2.92). Crystal structure, morphology and luminescence (excitation, emission and CIE coordinate) properties of these phosphors have been studied as a function of Ca concentration. Doping of Ca ions into Sr_2.92Ga₂O₆:Eu³⁺ phosphor gives rise to a significant enhancement in overall fluorescence and the optimum emission is attained for pure Ca_2.92Ga₂O₆:Eu³⁺ phosphor for x = 2.92. The intensity ratio of ⁵D₀ → ⁷F₂ to ⁵D₀ → ⁷F₁ transitions (monochromaticity) of Eu³⁺ for different doping concentration of Ca suggests that asymmetry around the Eu³⁺ ion increases with increase in Ca ion concentration, which is responsible for enhanced emission. The excellent optical features, such as broad excitation band (230–480 nm) and excellent emission in red region (at 614 nm), conclude that calcium gallet phosphor could be a potential candidate for light emitting diodes and display applications.     

Influence of high pressure on Sr2SiO4:Eu2+ luminescence

Eu²⁺ doped Sr₂SiO₄ phosphors were synthesized by solid state synthesis technique. The purity and crystal structure of the materials was studied with the X-ray powder diffraction. Depending on the synthesis method the materials contain one (α′) or two (α′ + β) crystal phases. Luminescence properties were studied in UV–Vis range at ambient and high hydrostatic pressure. Two broad emission bands in the yellow–orange and blue–green region were attributed to the 9-fold coordinated and 10-fold coordinated Eu²⁺, respectively. We found that increasing pressure causes a red shift of the yellow–orange emission. This is typical pressure dependence related to 4f⁶5d¹ → 4f⁷ transition in Eu²⁺ observed also in other materials. In the case of blue–green band, when pressure increases from ambient to 50 kbar, the emission band shifts strongly to higher energy, and for pressure higher than 50 kbar does not depend on pressure. This effect was considered in framework of crystal field model. We presumed that electrostatic field in a 10-fold coordinated site is a superposition of crystal field of four ligands that belong to tetrahedral coordination and six ligands belonging to octahedral coordination. We discussed untypical pressure dependence of the blue–green emission band as a result of pressure influence on the lower excited state in Eu²⁺, i.e. 4f⁶5d¹(e) at octahedral and 4f⁶5d¹(t) at tetrahedral coordination.     

Photoluminescence mechanisms of color-tunable Sr2CeO4: Eu3+, Dy3+ phosphors based on experimental and first-principles investigation

We report single-phased color-tunable phosphors (Sr₂CeO₄: Eu³⁺, Dy³⁺) synthesized by a polymer-network gel method for UV–LED. The photoluminescence properties and possible energy transfer mechanisms of Eu³⁺ and Dy³⁺ in Sr₂CeO₄ were investigated by experiments and first principles calculations. The results show that the ⁵D₀ → ⁷F₂ emission of Eu³⁺ is enhanced by the increase in the amount of Eu³⁺ ions and Eu³⁺ substitution makes more stable defect than Dy³⁺ substitution does. The photoluminescence mechanism of Sr_1.994−xEu_xDy_0.006CeO₄ can be explained by the energy transfer model with the consideration of the defect conditions in the crystals.     

Photoluminescence spectra tuning of Eu2+ activated orthosilicate phosphors used for white light emitting diodes

Divalent europium activated alkaline earth orthosilicate M₂SiO₄ (M = Ba, Sr, Ca) phosphors were synthesized through solid-state reaction technique and their luminescent properties were investigated. Photoluminescence emission spectra of Sr₂SiO₄:Eu²⁺ phosphor was tuned by substitution of Sr²⁺ with 10 mol% Ca²⁺ or Mg²⁺. Two emission bands originated from the 4f–5d transition of Eu²⁺ ion doped into different cation sites in the M₂SiO₄ host lattice were observed under ultraviolet excitation. The Sr₂SiO₄:Eu²⁺ phosphor showed a blue and a green broad emission bands peaked around 475 and 555 nm with some variation for different Eu²⁺ doping concentration. When 10 mol% of Sr²⁺ was substituted by Ca²⁺ or Mg²⁺, the blue emission band blue-shifted to 460 nm and the green emission band shifted to even longer wavelength. An energy loss due to energy transfer from one Eu²⁺ to another Eu²⁺ ion, changing of the crystal field strength and covalence in the host lattice together were assigned for the tuning effect. With an overview of the excitation spectra and the emission spectra in blue and green-yellow color, these co-doped phosphors can become a promising phosphor candidate for white light-emitting-diodes (LEDs) pumped by ultraviolet chip.