Frequency-conversion properties of Eu doped chlorophosphate glass ceramics containing CaCl2 nanocrystals

Eu³⁺ ion doped chlorophosphate glass ceramics containing nanocrystals were successfully prepared, and their spectroscopic characterizations were done using absorption, excitation and emission spectra. For the crystallized samples, X-ray diffraction (XRD) and transmission electron microscopy (TEM) experiments evidenced the formation of CaCl₂ nanocrystals. The absorption and emission spectra investigations indicate that a considerable amount of Eu³⁺ ions was trapped in CaCl₂ nanocrystals, and therefore an efficient up- and down-frequency conversion was observed. The comparative spectroscopic studies of Eu³⁺ doped samples suggest that the investigated glass ceramics systems are potentially applicable as frequency-conversion photonics devices.     

Synthesis, structure and optical properties of Eu/TiO2 nanocrystals at room temperature

The nanocrystal samples of titanium dioxide doped with europium ion (Eu³⁺/TiO₂ nanocrystal) are synthesized by the sol-gel method with hydrothermal treatment. The Eu³⁺ contents (molar ratio) in the samples are 0, 0.5%, 1%, 2%, 3% and 4%. The X-ray diffraction, UV-Vis spectroscopy data and scanning electron microscope image show that crystallite size is reduced by the doping of Eu³⁺ into TiO₂. Comparing the Raman spectra of TiO₂ with Eu³⁺/TiO₂ (molar ratio Eu³⁺/TiO₂=1%, 2% and 4%) nanocrystals at different annealing temperatures indicates that the anatase-to-rutile phase transformation temperatures of Eu³⁺/TiO₂ nanocrystals are higher than that of TiO₂. This is due to the formation of Eu-O-Ti bonds on the surface of the TiO₂ crystallite, as characterized by the X-ray photoelectron spectroscopy. The photoluminescence spectra of TiO₂ in Eu³⁺/TiO₂ nanocrystals are interpreted by the surface self-trapped and defect-trapped exciton relaxation. The photoluminescence of Eu³⁺ in Eu³⁺/TiO₂ nanocrystals has the strongest emission intensity at 2% of Eu³⁺ concentration.     

Synthesis, luminescence and crystallographic structure of Eu-doped garnet-type yafsoanite Ca3Te2(ZnO4)3

A red-emitting phosphor of Eu³⁺-doped calcium–tellurium–zinc oxide, Ca₃Te₂(ZnO₄)₃, with a garnet-type structure was synthesized by high temperature solid-state reactions. This phosphor exhibited a strong red emission. The photoluminescence excitation spectrum showed that Ca₃Te₂(ZnO₄)₃:Eu³⁺ can be effectively excited by UV–visible light. The property of long-wavelength excitation for this material has a benefit as a red phosphor in application of white light-emitting diodes. The colour coordinates were calculated. The excitation and emission spectra and luminescence decay curves were obtained using a pulsed, tunable, narrowband dye laser. Crystallographic sites and charge compensation mechanism of Eu³⁺ ions were discussed. The emission line from Eu³⁺ in intrinsic crystallographic site in the lattice was located at 579.56 nm. The emission line from Eu³⁺ in another disturbed site, which is created by the defects created by the charge-compensation, was located at 580.88 nm. The disordered crystallographic sites of Eu³⁺ are benefit for their strong red luminescence corresponding to the ⁵D₀→⁷F₂ transition.     

Optical properties of Eu-doped zinc borate glasses

Photoluminescence, absorption and optical excitation spectra of undoped and Eu³⁺-doped binary zinc borate glasses of varied composition prepared by the melt quenching technique in air atmosphere were investigated. From photoluminescence measurements it was found that growing Eu³⁺ concentration leads to gradual disappearance of the broadband glass emission in the near-UV spectral range, while the red Eu³⁺ emission at 613 nm shows a considerable increase. This result together with excitation spectra suggests that the Eu³⁺ ions are excited via energy transfer from the initially excited glassy host. The glass composition strongly affects the position of the excitation maximum in the UV energy range.     

Structural and optical properties of the nanopowder of the Eu3+ doped LiLaP4O12 produced by sol gel route

Structural and optical properties of nanopowders of Eu³⁺-doped LiLaP₄O₁₂ (LiLaPO) were studied. The samples were synthetized via polyvinyl alcohol assisted sol gel method. Powder X-ray diffraction (XRD) results showed that the samples have the LiLaPO crystalline phase and scanning electron microscopy (SEM) showed that the particles are in the nanometer scale, mostly as isolated particles with same aggregates. Photoluminescence (PL) properties were evaluated via excitation and emission spectra. The excitation spectra, in the range 2.6–13.8 eV, allowed the identification of the charge transfer band, 4f → 4f5d excitation, exciton formation and the interband excitation of the Eu³⁺ ions in the matrix. The emission spectra revealed that Eu³⁺ is located in two different sites in the samples, one of them being at the bulk and the other close to the surface of the nanoparticles, result confirmed by the CT excitation band.     

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.     

Spectral tuning and energy transfer in a potential fluorescent lamp phosphor BaMg2Al6Si9O30:Eu2+

BaMg₂Al₆Si₉O₃₀:Eu²⁺ phosphors are synthesized by the solid-state reaction method and their photoluminescence (PL) properties are investigated. The ultraviolet emission originates from Eu²⁺(I) substituting for Ba²⁺ sites, whereas the blue emission is attributed to Eu²⁺(II) substituting for Mg²⁺ sites. With increasing Eu²⁺ doping concentrations, the blue emission band shifts to long wavelength and the PL intensity ratio of blue to ultraviolet emission increases. Energy transfer between the two different Eu²⁺ ions is analyzed by photoluminescence excitation and emission spectra, and lifetimes. Results indicate that the emission spectra can be tuned by changing Eu²⁺ contents. We have also demonstrated that BaMg₂Al₆Si₉O₃₀:Eu²⁺ phosphor is a kind of potential phosphor for fluorescent lamps.     

Effect of concentration on the luminescence of Eu ions in nanocrystalline La2O3

Nanocrystalline powders with various Eu³⁺ concentration (from 1 to 10 mol %) doped La₂O₃ were prepared via a combustion route. Their structure and morphology were characterized using X-ray diffraction (XRD) and High-resolution transmission electron microscopy. The emission spectra of the as-synthesized samples show that the strongest emission position is centered at 626 nm corresponding to ⁵D₀→⁷F₂ transition of Eu³⁺ ions and the intensity change of 626 nm emission is considered as a function of ultraviolet (240 nm) irradiation time. The excitation spectra at 626 nm monitoring indicate that the charge transfer state band is varies with different Eu³⁺ ion concentration. These results are attributed to the surface defects of the nanocrystals.     

Photoluminescence properties of blue-emitting Li4SrCa(SiO4)2:Eu2+ phosphor for solid-state lighting

Blue-emitting Li₄SrCa(SiO₄)₂:Eu²⁺ phosphors have been synthesized by solid-state reaction. The photoluminescence (PL) excitation spectrum shows broad-band absorption and matches well with the emission of a near-UV (n-UV) chip. The PL emission spectrum exhibits a broad-band emission peaking at 430 nm, which is the characteristic emission of the f–d transition of the Eu²⁺ ion. The diffuse reflection spectra, temperature-dependent emission spectra, fluorescence decay, and mechanism of concentration quenching are also studied in detail. Li₄SrCa(SiO₄)₂:Eu²⁺ is a candidate blue phosphor for n-UV excited solid-state lighting.     

Eu2+激活的Ca3SiO5绿色荧光粉的制备和发光特性研究

研究了Eu²⁺激活的绿色发光材料Ca₃SiO₅的制备条件和发光性质. Eu²⁺中心形成主峰值为501 nm和次峰值为570 nm的特征宽带，两峰值叠加形成发射峰值为502nm的绿色发射光谱带. 利用这些光谱结果和Van Uitert 经验公式，确认Ca₃SiO₅:Eu²⁺中存在两种性质有差异的Eu²⁺发光中心，它们分别占据基质中八配位的Ca²⁺(Ⅰ)格位和四配位的Ca²⁺(Ⅱ)格位. 其激发光谱分布在250—450 nm的波长范围，峰值位于375 nm处，可以被InGaN管芯产生的350—410 nm辐射有效激发. 关键词： 发光 荧光粉 绿色荧光粉 3SiO₅')" href="#">Ca₃SiO₅ 2+')" href="#">Eu²⁺     

Luminescence of aggregate centers in CsBr:Eu2+ single crystals

We have used the Bridgman method to grow CsBr:Eu²⁺ single crystals, adding an activator to the mix in the form of Eu₂O₃ in amounts of 0.0125, 0.0250, and 0.0500 mole %. At T = 300 K, we studied the absorption spectra, the photoluminescence (PL) spectra, and the photostimulated luminescence (PSL) spectra of the grown crystals. We have established that the structure of the photoluminescence and photostimulated luminescence centers in crystals grown from the CsBr:Eu₂O₃ mix includes isolated dipole centers Eu²⁺-V_Cs, emitting in bands with maxima at 432 nm and 455 nm respectively, and in crystals grown at activator concentrations of 0.025 and 0.050 mole % they also include aggregate centers (AC) based on CsEuBr₃ nanocrystals with emission bands at 515 m and 523 nm. We have shown that the maximum concentration of aggregate centers of the CsEuBr₃ nanocrystal type in CsBr:Eu²⁺ crystals is achieved for an activator content in the mix within the range 0.01–0.05 mole %. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 359–362, May–June, 2006.     

Photoluminescence properties of Sr(Y, Gd)2O4:Euunder VUV excitation

Vacuum ultraviolet (VUV) excitation and photoluminescence (PL) properties of Sr(Y, Gd)₂O₄ doped with Eu³⁺ were studied. The excitation spectra of SrY_1.9Eu_0.1O₄ and SrY_1.0Gd_0.9Eu_0.1O₄ had absorption in the VUV region with the absorption band edge at 149 nm, while the absorption of SrGd_1.9Eu_0.1O₄ in the VUV region was weak, which could be due to the narrow host band gap and no efficient energy transfer occurred in the VUV region. The PL spectra of all samples exhibited the characteristic emission of Eu³⁺ with the red ⁵D₀-⁷F₂ transition (611 nm) being the most prominent group.     

The electronic structure and photoluminescence properties of Ca2GeO4:Eu in ultraviolet and vacuum ultraviolet region

Ca₂GeO₄:Eu³⁺ phosphors were synthesized by the solid state method. The ultraviolet and vacuum ultraviolet excited photoluminescence properties were investigated in detail. It revealed that the emission of Ca₂GeO₄:Eu³⁺ comprised two parts: the red emission of Eu³⁺ and host defect emission in 330-550 nm. Ca₂GeO₄:Eu³⁺ presented intense excitation intensity at 163-200 and 466 nm, which suggested the potential applications in plasma display panels and light emitting diodes. The excitation spectra were studied to identify the photoluminescence mechanisms of Ca₂GeO₄:Eu³⁺. First principles calculation within the local density approximation of the density functional theory was applied to calculate the electronic structure and linear optical properties of Ca₂GeO₄.     

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.     

Crystal growth,luminescence and scintillation properties of Eu2+:CeBr3 crystals

Eu²⁺:CeBr₃ crystals were grown by vertical Bridgman growth method and slight aliovalent doping of Eu²⁺ in the CeBr₃ crystal did not change the crystal structure. The X-ray stimulated luminescence, photoluminescence, decay kinetics and scintillation properties were investigated at room temperature. The X-ray stimulated luminescence spectra exhibited wide broad emission bands from 3.54 eV to 2.95 eV in the Eu²⁺:CeBr₃ crystal with high content of 620 ppm of Eu²⁺, which were the overlap of the emission bands ascribed to 5d → 4f transition of Ce³⁺ and 4f⁶5 d¹ → 4f⁷ transition of Eu²⁺, respectively. When the content of Eu²⁺ was decreased to 70 ppm, another emission band centered at 2.29 eV was observed. The photoluminescence spectra showed the energy transfer from Ce³⁺ to Eu²⁺. This decreased the Ce³⁺ emission intensity but enhanced the Eu²⁺ emission intensity. The photoluminescence decay time of Ce³⁺ emission decreased from 14 ns to 10 ns when the content of Eu²⁺ increased from 70 ppm to 620 ppm. The decay time of the emission of 525 nm did not change with the excitation wavelength and Eu²⁺ content, which could be assigned to the excitons that were bound on Eu²⁺ related centers. The light output of the Eu:CeBr₃ crystal under the excitation of ²⁴¹Am radioactive source was less than 20.2% of Tl:NaI crystal.     

Quantum cutting in Gd<Subscript>2</Subscript>SiO<Subscript>5</Subscript>: Eu<Superscript>3+</Superscript> by VUV excitation

The emission and excitation spectra of Gd₂SiO₅∶Eu³⁺ were investigated using the VUV beam line of the Beijing Synchrotron Radiation Facility (BSRF). The experimental results were discussed in the frame of visible quantum cutting process involved in Gd³⁺−Eu³⁺ system. Upon direct excitation into the⁶G _J states of Gd³⁺, two visible photon emissions from Eu³⁺ were observed. Cursory evaluation proved that Gd₂SiO₅∶Eu³⁺ is an efficient visible quantum cutter.     

Luminescence characteristics of energy transfer between Ce<Superscript>3+</Superscript> and Eu<Superscript>2+</Superscript> in NaMgPO<Subscript>4</Subscript> phosphor

Powder samples of NaMgPO₄ doped with Eu²⁺ and Ce³⁺ were prepared and their photoluminescence spectra were systemically studied. Energy transfer from Ce³⁺ to Eu²⁺ in NaMgPO₄ phosphor was observed by investigating the optical properties from photoluminescence spectra in Eu²⁺ or Ce³⁺ singly doped and Eu²⁺–Ce³⁺ codoped sodium magnesium orthophosphates, NaMgPO₄. The enhancement of UV excitation is attributed to energy transfer from Ce³⁺ to Eu²⁺, and Ce³⁺ plays a role as a sensitizer. Ce³⁺–Eu²⁺ codoped NaMgPO₄ phosphors in which Eu²⁺ can be efficiently excited by 390 nm are potential candidates for phosphor-converted LEDs.     

Change of the luminescence decay time for Lu<Subscript>2</Subscript>O<Subscript>3</Subscript>: Eu nanocrystals embedded in synthetic opal

The opal-Lu_1.86Eu_0.14O₃ composites have been prepared using the developed technique for synthesizing luminophor nanocrystals in pores of synthetic opal through coprecipitation from a solution. It has been demonstrated that the position of the photonic stop band in the reflection spectrum of the infiltrated opal depends on the diameter of its spheres, the volume fraction of the embedded luminophor, and the angle of detection of the signal. The excitation and photoluminescence spectra of the composites have been analyzed, and the lifetime of the ⁵ D ₀ excited state of Eu³⁺ ions has been examined. It has been revealed that the luminescence decay time for the luminophor increases by almost one order of magnitude with an increase in its content in opal pores. This effect has been attributed to the change in the nanocrystal size and to the decrease in the contribution from the surface nonradiative recombination in luminophor nanolayers of the composites.     

Intense green-emitting Sr2LiSiO4F:Eu2+ phosphor for n-UV white LEDs

Eu²⁺-activated Sr₂LiSiO₄F phosphors were synthesized at 900°C by solid-state reaction in reducing atmosphere, and their photoluminescence (PL) properties were systematically investigated by diffuse reflection spectra, PL excitation and emission spectra, and by the fluorescence decay curve. Sr₂LiSiO₄F:Eu²⁺ emits intense green light at 520 nm originating from the 5d¹4f⁶−4f⁷ transition of Eu²⁺ under 365 nm n-UV excitation. The PL excitation spectrum matches the emission from n-UV chips. These materials could be promising green phosphors for use in generating white light in phosphor-converted white light-emitting-diodes (LEDs).     

Luminescence thermometry using Gd<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript>:Eu<Superscript>3+</Superscript>

In this paper we study the possibility of using the synthesized nanopowder samples of Gd₂Zr₂O₇:Eu³⁺ for temperature measurements by analyzing the temperature effects on its photoluminescence. The nanopowder was prepared by solution combustion synthesis method. The photoluminescence spectra used for analysis of Gd₂Zr₂O₇:Eu³⁺ nano phosphor optical emission temperature dependence were acquired using continuous laser diode excitation at 405 nm. The temperature dependencies of line emission intensities of transitions from ⁵D₀ and ⁵D₁ energy levels to the ground state were analyzed. Based on this analysis we use the two lines intensity ratio method for temperature sensing. Our results show that the synthesized material can be efficiently used as thermographic phosphor up to 650 K.