Luminescent properties of SrMg<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Eu<Superscript>2+</Superscript>, and Mn<Superscript>2+</Superscript> as a potential phosphor for ultraviolet light-emitting diodes

Eu²⁺ and Mn²⁺ co-doped SrMg₂(PO₄)₂ phosphors with blue and red two emission bands were prepared by the high temperature solid state method and their luminescent properties have been investigated as a function of activator and co-activator concentrations. Resonance-type energy transfers from Eu²⁺ to Mn²⁺ were discovered by directly overlapping the Eu²⁺ emission spectrum and the excitation spectrum of Mn²⁺. Efficiencies of energy transfer were also calculated according to the changes of relative intensities of Eu²⁺ and Mn²⁺ emission. According to the principle of energy transfer, we demonstrated that the phosphor SrMg₂(PO₄)₂:Eu²⁺,Mn²⁺ with double emission bands exhibited a great potential as a phosphor for ultraviolet light-emitting diodes and the relative intensities of blue and red emission could be tuned by adjusting the contents of Eu²⁺ and Mn²⁺. PACS 78.55.-m     

Eu2+,Mn2+在BaZnP2O7中的发光及Eu2+→Mn2+能量传递

采用高温固相法合成了BaZnP₂O₇:Eu²⁺,Mn²⁺荧光粉,并对其发光性质及Eu²⁺对Mn²⁺的能量传递机理进行了研究.Eu²⁺和Mn²⁺在380 nm和670nm的发射峰分别由Eu²⁺的5d—4f跃迁和Mn²⁺的⁴T₁(^{4关键词： 磷酸盐 2+}')" href="#">Eu²⁺ 2+')" href="#">Mn²⁺ 能量传递     

Eu-Mn energy transfer in white-light-emitting T-phase (Ba,Ca)2SiO4:Eu, Mn phosphor

White-light-emitting T-phase Eu²⁺/Mn²⁺-codoped (Ba, Ca)₂SiO₄ phosphors are achieved in terms of the energy transfer between Eu²⁺ and Mn²⁺ ions. All spectra consist of the relatively broad green and the red emission bands, which thus result in a warm-white color with a color temperature of ∼4000 K. With increasing Eu²⁺ ions at fixed Mn²⁺ concentrations, a strong correlation between the luminescence and the electron paramagnetic resonance spectra is observed. This demonstrates that Eu²⁺ doping causes a perturbation of Mn²⁺ sites and the violation of their selection rules that enhances Mn²⁺-related emissions.     

Luminescence spectroscopy and energy transfer in Eu2+/Mn2+-doped KCaPO4 phosphors

Eu²⁺/Mn²⁺-doped KCaPO₄ phosphors were prepared by conventional solid-state reaction. X-ray powder diffraction (XRD), SEM, photoluminescence excitation, and emission spectra, and the luminescence decay curves were measured. Mn²⁺ singly doped KCaPO₄ shows the weak origin-red luminescence band peaked at about 590 nm. The Eu²⁺/Mn²⁺ co-doped phosphors emit two distinctive luminescence bands: a blue one centered at 480 nm originating from Eu²⁺ ions and a broad red-emitting one peaked at 590 nm from Mn²⁺ ions. The luminescence intensity from Mn²⁺ ions can be greatly enhanced with the co-doping of Eu²⁺ ions. The efficient energy transfer from Eu²⁺ to Mn²⁺ was verified by the photoluminescence spectra together with the luminescence decay curves. The resonance-type energy transfer via a dipole–quadrupole interaction mechanism was supported by the decay lifetimes. The emission colors could be tuned by changing the Mn²⁺-doping concentration.     

Luminescence and energy transfer in Eu2+,Mn2+ codoped Na2BaMgP2O8 phosphor

Eu²⁺ single-doped and Eu²⁺/Mn²⁺-codoped Na₂BaMgP₂O₈ phosphors were prepared by a combustion-assisted synthesis method. The phase formation was confirmed by X-ray powder diffraction measurement. Na₂BaMgP₂O₈:Eu²⁺,Mn²⁺ shows a broad blue emission band and a red emission band, which originate from Eu²⁺ occupying the Ba²⁺ sites and Mn²⁺ occupying the Mg²⁺ sites, respectively. The efficient energy transfer from Eu²⁺ to Mn²⁺ is verified by the excitation and emission spectra together with the luminescence decay curves. Based on the principle of energy transfer, the relative intensities of blue and red emissions could be tuned by adjusting the contents of Eu²⁺ and Mn²⁺.     

长波紫外激发下的三基色发光玻璃

报道了一种新的可用长波紫外有效激发的三基色发光玻璃.这种三基色荧光玻璃样品是在相同硅硼酸盐基质中掺杂Ce³⁺/Mn²⁺, Ce³⁺/Tb³⁺以及Eu²⁺并采用熔融法制备出的.其中Mn²⁺,Tb³⁺,Eu²⁺作为激活离子,Ce³⁺作为敏化剂向激活离子提供能量.由于敏化剂的加入使这种三基色发光玻璃在长波紫外激发下获 关键词： 三基色发光 能量传递 长波紫外 发光玻璃     

Photoluminescence properties of color-tunable SrMgAl10O17:Eu2+,Mn2+ phosphors for UV LEDs

Aluminate phosphors SrMgAl₁₀O₁₇ codoped with Eu²⁺ and Mn²⁺ ions were prepared by solid-state reaction. The phase structure and photoluminescence properties of the as-prepared phosphors were characterized by powder X-ray diffraction, photoluminescence excitation and emission spectra. Upon excitation of UV light, two broad emission bands centered at 470 and 515 nm were observed, and they were assigned to Eu²⁺ and Mn²⁺ emissions, respectively. The emission color of the phosphors can be tuned from blue to cyan and finally to green by adjusting the concentration ratios of Eu²⁺ and Mn²⁺. Effective energy transfer occurs from Eu²⁺ to Mn²⁺ in the host due to the spectral overlap between the emission band of Eu²⁺ and the excitation bands of Mn²⁺. The energy transfer mechanism was demonstrated to be electric dipole–quadrupole interaction. The energy transfer efficiency and critical distance were also calculated. The phosphors exhibit strong absorption in near UV spectral region and therefore they are potentially useful as UV-convertible phosphors for white LEDs.     

Luminescent properties of Sr5(PO4)3 Cl:Eu2+, Mn2+ as?a?potential phosphor for UV-LED-based white LEDs

Eu²⁺ and Mn²⁺ co-activated Sr₅(PO₄)₃Cl phosphors with blue and orange color double emission bands, under a broad-band excitation wavelength range of 340–400 nm, were synthesized by the solid-state reaction. It was found that the processing parameters, including the fluxes, annealing time and activators concentrations, affect the emission intensity and other luminescent properties. Energy transfer between Eu²⁺ and Mn²⁺ was discovered and the transfer efficiency was also estimated based on relative intensities of Eu²⁺ and Mn²⁺ emission. Thus the relative strength of blue and orange emission intensities could be tuned by varying the relative concentration of Eu²⁺ and Mn²⁺. Since the photoluminescence excitation spectra of the newly developed Sr₅(PO₄)₃Cl:Eu²⁺, Mn²⁺ phosphors exhibit a strong absorption in the range of 340–400 nm, they are promising for producing UV-LED-based white LEDs.     

用于白光LED的单一基质白光荧光粉Ca2SiO3Cl2:Eu2+，Mn2+的发光性质

用高温固相法合成了Eu²⁺，Mn²⁺共激活的Ca₂SiO₃Cl₂高亮度白色发光材料，并对其发光性质进行了研究. 该荧光粉在近紫外光激发下发出强的白色荧光，Eu^{2+中心形成峰值为419 nm和498 nm的特征宽带，通过Eu2+中心向Mn2+中心的能量传递导致了峰值为578 nm的发射，三个谱带叠加从而在单一基质中得到了白光. 激发光谱均分布在250—415 nm的波长范围，红绿蓝三个发射带的激发谱峰值分别位于385 nm，412 nm，370 nm和396 nm处，可以被InGaN管芯产生的紫外辐射有效激发. Ca₂SiO₃Cl₂:Eu2+，Mn2+是一种很有前途的单一基质白光LED荧光粉.}     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu³⁺ ions.     

Cooperative absorption in Eu2O2S

Lines due to cooperative optical absorption of Eu³⁺ have been observed in the luminescence excitation spectra for Eu₂O₂S at 75 K. A pair of Eu³⁺ ions are simultaneously excited by one photon to the ⁵D_J and ⁷F'_J states from the ground state ⁷F₀. Estimated oscillator strengths of the pair absorption are of the order of 10^-9, and are much larger than those in other rare earth compounds reported elsewhere. Multipolar interaction between Eu³⁺ ions cannot explain such a large oscillator strength. Hole-exchange through the charge transfer state, or a super-exchange mechanism, gives a reasonable order of the pair absorption strength in Eu₂O₂S.     

Photoluminescence of double-color-emitting phosphor Ca5(PO4)3Cl:Eu, Mn for near-UV LED

Eu²⁺ activated Ca₅(PO₄)₃Cl blue-emitting phosphors were prepared by the conventional solid state method using CaCl₂ as the chlorine source and H₃BO₃ as flux. The structure and luminescent properties of phosphors depend on the concentrations of Eu²⁺, the amount of CaCl₂ and the usage of the H₃BO₃ flux were investigated systematically. Eu²⁺ and Mn²⁺ Co-doped Ca₅(PO₄)₃Cl with blue and orange double-band emissions were also researched based on the optimal composition and synthesis conditions. The energy transfer between Eu²⁺ and Mn²⁺ was found in the phosphor Ca₅(PO₄)₃Cl:Eu²⁺, Mn²⁺, and the Co-doped phosphor can be efficiently excited by near-UV light, indicating that the phoshor is a potentional candidate for n-UV LED used phosphor.     

White light emitting from single phased K2Ca1−x−yP2O7: xEu, yMn phosphors under UV excitation

A single phased white light emitting phosphors K₂Ca_1−x−yP₂O₇: xEu²⁺, yMn²⁺ were synthesized by solid state reaction method. The Effective energy transfer occurs in this phosphor due to the large spectral overlap between the emission of Eu²⁺ and the excitation of Mn²⁺. The emission hue of K₂Ca_1−x−yP₂O₇: xEu²⁺, yMn²⁺ from blue to white light can be obtained by tuning the Eu²⁺/Mn²⁺ content ratio. The energy transfer mechanism from Eu²⁺ to Mn²⁺ in this phosphor was carefully investigated and demonstrated to be via the dipole–quadrupole interaction.     

Nonradiative energy transfer from Mn2+ to Eu3+ in K2CaP2O7:Mn2+,Eu3+ phosphor

A series of color tunable phosphors K₂Ca_1?x?yP₂O₇:xMn²⁺, yEu³⁺ are synthesized by solid state reaction method. The energy transfer phenomenon from Mn²⁺ to Eu³⁺ has been observed in the Mn²⁺/Eu³⁺ codoped non-magnetic K₂CaP₂O₇ host, which was confirmed by PL spectra and decay curves. The Mn²⁺→Eu³⁺ energy transfer is controlled by quadrupole–quadrupole interaction between sensitizer and activator. The maximum efficiency of energy transfer is estimated to be 33% with x=0.125 and y=0.03 in K₂Ca_1?x?yP₂O₇:xMn²⁺, yEu³⁺ phosphor. The phosphors can emit light from green to yellow and eventually to orange under 400 nm excitation by changing the Mn²⁺/Eu³⁺ content ratio, indicating that K₂CaP₂O₇: Mn²⁺, Eu³⁺ would be potential candidates for use in lighting and displays applications.     

Fluorescence emission spectrum and energy transfer in Eu and Mn co-doped Ba2Ca(BO3)2 phosphors

Eu²⁺ and Mn²⁺ co-doped Ba₂Ca(BO₃)₂ phosphors yield two emission bands consisting of green and red components under the excitation of 360 nm, which shows a great potential for white LEDs. Effective energy transfer occurs in Eu²⁺/Mn²⁺ co-doped Ba₂Ca(BO₃)₂ host due to the large spectral overlap between the emission of Eu²⁺ and the excitation of Mn²⁺. The energy transfer from Eu²⁺ to Mn²⁺ is thoroughly investigated by their excitation, emission and photoluminescence decay behaviors, and is demonstrated to be via the dipole–quadrupole interaction.     

Luminescence properties and energy transfer in Eu2+, Mn2+ codoped Na(Sr,Ba)PO4 phosphor

Eu²⁺ and Mn²⁺ singly doped and codoped Na(Sr,Ba)PO₄ phosphors were synthesized, and their luminescent properties were investigated. A broad blue emission and a broad orange emission band were observed in Na(Sr,Ba)PO₄:Eu²⁺, Mn²⁺ phosphor. The resonant-type energy transfer from Eu²⁺ to Mn²⁺ was demonstrated, and the energy transfer efficiency was also calculated according to their emission spectra. Based on the principle of energy transfer, the emission intensity ration of Eu²⁺ and Mn²⁺ could be appropriately tuned by adjusting the contents of activators. Due to the strong absorption in the 250–400 nm range, Na(Sr,Ba)PO₄:Eu²⁺, Mn²⁺ phosphor could be used as a potential candidate for near-UV white light-emitting diodes (LEDs).     

Photoluminescence properties of Eu and Mn-activated BaMgP2O7 as a potential red phosphor for white-emission

A phosphate compound, BaMgP₂O₇ was co-doped with Eu²⁺ and Mn²⁺ for making a red-emitting phosphor. The phosphor was prepared by a solid-state reaction at high temperature. The photoluminescence properties were investigated under ultraviolet (UV) ray excitation. From a powder X-ray diffraction (XRD) analysis, the formation of single-phased BaMgP₂O₇ with a monoclinic structure was confirmed. In the photoluminescence spectra, the BaMgP₂O₇:Eu,Mn phosphor emits two distinctive colors: a blue band centered at 409 nm originating from Eu²⁺ and a red band at 615 nm caused by Mn²⁺. Also, efficient energy transfer from Eu²⁺ to Mn²⁺ in the BaMgP₂O₇:Eu,Mn system was verified by observing that the excitation spectra of BaMgP₂O₇:Eu,Mn emitted at 409 and 615 nm by Eu²⁺ emission and Mn²⁺ emission, respectively, are almost the same as that of BaMgP₂O₇:Eu monitored at 409 nm. The optimum concentration of Eu²⁺ ions in BaMgP₂O₇:0.015Eu excited at 309 nm wavelength is 1.5 mol%. With an increase of Mn²⁺ content up to 17.5 mol%, a systematic decline in the intensity of the excitation spectrum by Eu²⁺ and a gradual growth in the intensity of emission band by Mn²⁺ were observed. Accordingly, the optimum concentration of Mn²⁺ in BaMgP₂O₇:0.015Eu,Mn is 17.5 mol%. The maximum spectral overlap between emission of Eu²⁺ and excitation of Mn²⁺ is achieved in a composition of BaMgP₂O₇:0.015Eu,0.175Mn, resulting in considerable red-emission at 615 nm.     

Emission properties of Eu, Mn in MAl2Si2O8 (M=Sr, Ba)

The emission properties of Eu²⁺ and Mn²⁺ in monoclinic SrAl₂Si₂O₈ (M-SAS) and hexagonal BaAl₂Si₂O₈ (H-BAS), both of which have only one alkaline-earth site, were studied. The emission peaks of both Eu²⁺ (405 nm) and Mn²⁺ (564 nm) in SrAl₂Si₂O₈, are located at longer wavelengths, compared with those in H-BAS (373 nm for Eu²⁺ and 518 nm for Mn²⁺), because of the stronger crystal field strength at the Sr site. EPR spectra showed that the g values of Mn²⁺ are 4.5065 in M-SAS:Mn and 2.0247 in H-BAS:Mn. Magnetic measurements proved that Mn²⁺ was at high-spin state in both hosts. The large g value of Mn²⁺ in M-SAS was ascribed to the mixing of the first excitation state to the ground state, both of which have lower d orbital degeneracy due to the lower symmetry of Mn²⁺ site. The transfer efficiency from Eu²⁺ to Mn²⁺was about 10% in M-SAS, higher than that in H-BAS (5%). This was probably because Eu²⁺ emission overlaps the relatively low excitation level of Mn²⁺ in M-SAS. In order to obtain high transfer efficiency, it was necessary for the Eu²⁺ emission to overlap the lowest excitation level of Mn²⁺. The results obtained in this work may be helpful to design the new white or red phosphors for white-light emitting diode (w-LED) applications.     

Sensitized photoluminescent properties of manganese-activated magnesium gallate phosphor

The vaccum-ultra-violet (VUV)- and UV-excited luminescent properties of MgGa₂O₄:Mn²⁺ phosphor with various co-dopants were investigated. Spinel-structured manganese-activated magnesium gallate exhibited intense green emission with the spectrum centered at 503 nm under 147 and 254 nm excitation induced by the transition from the lowest excited state to the ground state, ⁴T₁-⁶A₁, of the tetrahedral-sited Mn²⁺. With optimized incorporation ranges, Eu³⁺, Ce³⁺ and Al³⁺ co-doping, enhanced the overall fluorescence efficiency under 147 nm and these could be tentatively interpreted in terms of optical properties of host compounds and co-doped ions.     

Fluorescence properties of divalent and trivalent europium ions in CdWO4 single crystals grown by Bridgman method

Optical absorption, excitation, and fluorescence were investigated in Eu ion-doped CdWO₄ single crystal grown by a modified Bridgman method. The results indicate that Eu²⁺ and Eu³⁺ ions coexist in CdWO₄ crystal and an energy transfer occurs between these Eu²⁺ and Eu³⁺ ions. When the crystal is excited by 266-nm light, the energy corresponding to the 4f⁶5d to ⁸S_7/2 transition of Eu²⁺ ions results in the excitation of the Eu³⁺ ions to the ⁵D_J level. The effect on fluorescence of annealing in oxygen at various temperatures was investigated. The excitation intensity of Eu²⁺ ions at 266 nm decreases as annealing temperature increases from 300 K to 1073 K, but it remains at a certain equilibrium level when the annealing temperature is further increased.