Mechanism of energy transfer in Sr2CeO4:Eu3+ phosphor

Blue–white phosphor Sr₂CeO₄ belongs to a particular class of optical materials whose luminescence is governed by optical transitions associated with the electron charge transfer. The originality of its crystallographic structure, a chain-like sequence of luminescent centers, permits an effective transfer of the electronic excitation energy from the host to doped centers. Sr₂CeO₄, рure and doped with Eu³⁺-ions of different concentrations, was synthesized by the Pechini citrate-gel method. The luminescence spectra and luminescence decay curves of Sr₂CeO₄ and Sr₂CeO₄:Eu³⁺ at 300 and 80 K were investigated. The performed experiments revealed the Förster nonradiative energy transfer under the energy migration condition from the crystal host to the doped europium ions.     

Persistence energy transfer between inequivalent Eu2+ ions in CaAl2Si2O8:Eu2+

Persistence energy transfer between Eu²⁺ ions in CaAl₂Si₂O₈:Eu²⁺ has been observed, which mainly due to the complexity of the system, brought about by the different crystallographic sites.With the increase of Eu²⁺ concentration, a persistent down-converted afterglow from blue to green was observed due to efficient persistence energy transfer from Eu₁ to Eu₂ which located at inequivalent sites in CaAl₂Si₂O₈:0.19Eu²⁺. When some of the trapped carries are released from the traps (T₁) via thermal activation, they are returned to the excited state of Eu₁, and rapidly transfer their energy to Eu₂, which contribute to the observation of tunable persistent color.     

Non-radiative energy transfer between Gd3+ and Eu2+ in cubic RbGd3F10

The mechanism of energy transfer between Gd³⁺ and Eu²⁺ in the cubic form of RbGd₃F₁₀ fluoride has been studied at room temperature and at liquid nitrogen temperature. The decay curves of the emission from the Gd³⁺⁶P_7/2 state were obtained for various concentrations of Eu²⁺ acceptor ions. The experimental curves have been fitted to Yokota and Tanimoto's equation and diffusion constant and interaction parameters are proposed.     

Characterization of various Eu2+ sites in Ca2SiO4:Eu2+ and Ba2SiO4:Eu2+ by high-pressure spectroscopy

Photoluminescence of Ba₂SiO₄ and Ca₂SiO₄ activated with Eu²⁺ was investigated at various temperatures (from 10 K to 300 K) and pressures (from ambient to 200 kbar). At ambient pressure and room temperature, under UV excitation both phosphors yielded a green emission band with maxima at 505 nm and 510 nm for Ba₂SiO₄ and Ca₂SiO₄, respectively. The energies of these bands depended on pressure; the pressure shifts were ?12:55 cm^?1/kbar for Ba₂SiO₄:Eu²⁺; and ?5:59 cm^?1/kbar for Ca₂SiO₄:Eu²⁺. In the case of Ca₂SiO₄:Eu²⁺, we observed additional broadband emission at lower energies with a maximum at 610 nm (orange band). The orange and green emission in Ca₂SiO₄:Eu²⁺ had different excitation spectra: the green band could be excited at wavelengths shorter than 470 nm, whereas the orange band — at wavelengths shorter than 520 nm. The pressure caused a red shift of orange emission of 7.83 cm^?1/kbar. The emission peaked at 510 nm was attributed to the 4f⁶5d→4f⁷(⁸S₇₌₂) transition of Eu²⁺ in the β — Ca₂SiO₄:Eu²⁺ phase, whereas the emission peaked at 610 nm — to the γ — Ca₂SiO₄:Eu²⁺ phase. The emission of Ba₂SiO₄:Eu²⁺ peaked at 505 nm was attributed to the 4f⁶5d→ 4f⁷(⁸S_7/2) transition of Eu²⁺ in the β — Ba₂SiO₄ phase.     

Eu~(2+),Mn~(2+)在CaZn_2(PO_4)_2中的发光及Eu~(2+)→Mn~(2+)能量传递

Mn2+作为激活剂加入一些基质中,发光比较弱。因此常常选择使用合适的敏化剂来提高Mn2+的发光效率,本文的研究目就是验证Eu2+是Mn2+的良好的敏化剂。采用高温固相法合成了Eu2+,Mn2+掺杂激活的CaZn2(PO4)2荧光粉,并对其发光性质进行了研究。单掺杂Eu2+时呈现发射峰位于504nm的带谱,属于Eu2+离子的5d-4f能级跃迁辐射,激发峰位于380nm,属于Eu2+的f-d跃迁特征激发谱带。单掺Mn2+时CaZn2(PO4)2不发光。当Eu2+和Mn2+共掺时,出现Mn2+的673nm发射峰,样品发红光,表明Eu2+对Mn2+的发光有很强的敏化作用。研究了Eu2+和Mn2+掺杂浓度对激发光谱和发射光谱的影响,证明在CaZn2(PO4)2:Eu2+,Mn2+中Eu2+对Mn2+的能量传递属于共振能量传递。     

Investigation of energy absorption and transfer process of Tb3+ or Eu3+ excited Na3Gd(PO4)2 in the VUV region

Na₃Gd(PO₄)₂, Na₃Gd_0.94(PO₄)₂:0.06Tb³⁺ and Na₃Gd_0.94(PO₄)₂:0.06Eu³⁺ are prepared by solid-state reaction and their photoluminescence (PL) properties are investigated in the ultraviolet (UV) and vacuum ultraviolet (VUV) region. The obtained results show that Na₃Gd_0.94(PO₄)₂:0.06Tb³⁺ has an efficient emission under 147 nm excitation, but the emission efficiency of Na₃Gd_0.94(PO₄)₂:0.06Eu³⁺ is low under 147 nm excitation. We discuss the energy absorption and transfer process in the VUV region to solve the special phenomenon.     

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.     

Mechanism of energy transfer in Sr2CeO4:Eu phosphor

Blue–white phosphor Sr₂CeO₄ belongs to a particular class of optical materials whose luminescence is governed by optical transitions associated with the electron charge transfer. The originality of its crystallographic structure, a chain-like sequence of luminescent centers, permits an effective transfer of the electronic excitation energy from the host to doped centers. Sr₂CeO₄, рure and doped with Eu³⁺-ions of different concentrations, was synthesized by the Pechini citrate-gel method. The luminescence spectra and luminescence decay curves of Sr₂CeO₄ and Sr₂CeO₄:Eu³⁺ at 300 and 80 K were investigated. The performed experiments revealed the Förster nonradiative energy transfer under the energy migration condition from the crystal host to the doped europium ions.     

Powder synthesis and white light-emitting properties of Eu3+ co-doped K2CaP2O7:Dy3+ phosphors with energy transfer between Dy3+ and Eu3+

A series of white-emitting K₂CaP₂O₇:Dy³⁺ and K₂CaP₂O₇:Dy³⁺, Eu³⁺ phosphors were synthesized via a solid-state method, and Eu³⁺ was co-doped in K₂CaP₂O₇:Dy³⁺ to improve its white light performance. The influences of preparation temperature and Dy³⁺/Eu³⁺ concentration on the crystal structure and photoluminescence characteristics were investigated. XRD results indicate that K₂CaP₂O₇:Dy³⁺ samples prepared above 700 °C matches the standard K₂CaP₂O₇ phase. Under excitation of 349 nm, K₂CaP₂O₇:Dy³⁺ phosphor exhibited characteristic emission peaks at 487 nm (blue) and 579 nm (yellow), and white emission was realized through combining these blue and yellow emissions. After co-doping Eu³⁺ ions, the co-luminescence of Dy³⁺/Eu³⁺ with energy transfer between Dy³⁺and Eu³⁺ were demonstrated. The chromaticity of white light was controlled by changing the ratio of Dy³⁺/Eu³⁺ concentrations, which lead to a warm white light. Therefore, the results indicate that K₂CaP₂O₇:Dy³⁺, Eu³⁺ powders have a potential application in w-LEDs as single-component white-emitting phosphor.     

Efficient doping and energy transfer from ZnO to Eu3+ ions in Eu(3+)-doped ZnO nanocrystals

Successful doping of Eu3+ ions into ZnO nanocrystals has been realized by using a low temperature wet chemical doping technique. The substitution of Eu3+ for Zn2+ is shown to be dominant in the Eu-doped ZnO nanocrystals by analyzing the X-ray diffraction patterns, transmission electron microscopy images, Raman and selectively excited photoluminescence spectra. Measurement of the luminescence from the samples shows that the excited ZnO transfers the excited energy efficiently to the doped Eu3+ ions, giving rise to efficient emission at red spectral region. The red emission quantum yield is measured to be 31% at room temperature. The temperature dependence of photoluminescence and the photoluminescence excitation spectra have also been investigated, showing strong energy coupling between the ZnO host and Eu3+ ions through free and bound excitons. The result indicates that Eu3+ ion-doped ZnO nanocrystals are promising light-conversion materials and have potential application in highly distinguishable emissive flat panel display and LED backlights.     

Photo- and thermoluminescence of BaGa2S4:Eu2+ and BaGa2S4:Eu2+,Ce3+ crystals

Data are presented on the photo- and thermoluminescence of polycrystalline BaGa₂S₄:Eu²⁺ and BaGa₂S₄:Eu²⁺, Ce³⁺ at temperatures from 77 to 300 K. The broad photoluminescence band at 505 nm in BaGa₂S₄:Eu²⁺ is shown to be due to the 4f ⁶5d → 4f ⁷ transition. The broad emission bands at 460 and 510 nm in BaGa₂S₄:Ce³⁺ arise from the 5D (² D _3/2) → 4f ²(² F _5/2) and 5D (² D _3/2) → 4f ²(² F _7/2) transitions. Codoping of BaGa₂S₄ with Eu²⁺ and Ce³⁺ increases the luminescence efficiency owing to energy transfer from Ce³⁺ to Eu²⁺. The thermoluminescence data were used to evaluate the energies of the traps involved: 0.26, 0.31, 0.42, 0.57, and 0.64 eV in BaGa₂S₄:Eu²⁺ and 0.28, 0.32, 0.54, 0.61, and 0.65 eV in BaGa₂S₄:Eu²⁺, Ce³⁺. Original Russian Text ? A.N. Georgobiani, B.G. Tagiev, S.A. Abushov, O.B. Tagiev, Zheng Xu, Suling Zhao, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 2, pp. 151–155.     

Strong luminescence and efficient energy transfer in Eu3+/Tb3+-codoped ZnO nanocrystals

Single crystalline Eu³⁺/Tb³⁺-codoped ZnO nanocrystals have been synthesized by using a simple co-precipitation method. Successful doping is realized so that strong green and red luminescence can be efficiently excited by ultraviolet and near ultraviolet radiation, demonstrating an efficient energy transfer from ZnO host to rare earth ions. The energy transfer from the ZnO host to Tb³⁺ in ZnO: Tb³⁺ samples and ZnO host to Eu³⁺ in the ZnO: Eu³⁺ samples under UV excitation are investigated. It is found that the red ⁵D₀ → ⁷F₂ emission of Eu³⁺ ions decreases with increasing temperature but the green ⁵D₄ → ⁷F₅ emission of Tb³⁺ ions increases with increasing temperature, implying a different energy transfer processes in the two samples. Moreover, energy transfer from Tb³⁺ ions to Eu³⁺ ions in ZnO nanocrystals is also observed by analyzing luminescence spectra and the decay curves. By adjusting the doping concentration, the Eu³⁺/Tb³⁺-codoped ZnO phosphors emit green and red luminescence with chromaticity coordinates near white light region, high color purity and high intensity, indicating that they are promising light-conversion materials and have potential in field emission display devices and liquid crystal display backlights.     

Luminescence and energy transfer of Sm3+/Eu3+ co-doped transparent glass ceramics

Journal of Materials Science: Materials in Electronics - The Sm3+/Eu3+ doped transparent glass ceramics (GCs) containing Na7.15(Al7.2Si8.8O32) crystallite were successfully prepared by melt...     

Multiple energy transfer between CaNb2O6:Tb3+, Eu3+ for single-component white light-emitting phosphors

Journal of Materials Science: Materials in Electronics - A series of host-activated Tb3+ and Eu3+-co-doped CaNb2O6 (CNO) phosphors with tunable luminescence were synthesized via high-temperature...     

Luminescent properties of Li2CaSiO4:Eu2+ phosphor

Li₂CaSiO₄:Eu²⁺ phosphors with single phase were successfully synthesized by the solid state reaction method and their photoluminescence properties were studied. The experimental results on Li₂CaSiO₄:Eu²⁺, summarized in effective absorption and excitation in the ultra-violet region, strong emission in the blue spectrum and the CIE Chromaticity coordinate (0.10, 0.20), indicate this phosphor has great potential in ultra-violet chip pumped white LEDs. A comparative investigation of the emission intensity suggests that Li₂CaSiO₄:Eu²⁺ has the best performance with Eu²⁺ concentration of 1% and excitation of 375 nm. Compound phosphors of Li₂CaSiO₄:Eu²⁺ and Li₂SrSiO₄:Eu²⁺ show two emission bands in the blue and yellow region. With the molar ratio of Li₂CaSiO₄:Eu²⁺ to Li₂SrSiO₄:Eu²⁺ being 1:1 and excitation of 390 nm, the CIE Chromaticity coordinate was tuned to be (0.32, 0.36), which is close to that of natural white light, indicating this may become blue phosphor candidate for ultra-violet chip pumped and multi-phosphors converted white LEDs.