Luminescent properties of YAl3(BO3)4:Eu3+ phosphors

YAL₃(BO₃)₄:Eu³⁺ phosphors were fabricated by the sol-gel method. The structure properties were measured by x-ray diffraction (XRD) and infrared spectra (IR). Doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors of 0, 1, 3, 4, and 5 mol% were studied. The excitation spectra and emission spectra of YAL₃(BO₃)₄:Eu³⁺ phosphors were examined by fluorescent divide spectroscopy (FDS). The luminescent properties of YAL₃(BO₃)₄:Eu³⁺ phosphors are discussion. The optimal doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors was found to be approximately 3 mol%.     

Photoluminescence investigation of rare-earth activated GdCa3(GaO)3(BO3)4 phosphors under UV excitation

A borate compound was adopted as a new host material of Eu³⁺ and Tb³⁺ activators to fabricate efficient luminescence materials. The phosphor compositions, Gd_1−xEu_xCa₃(GaO)₃(BO₃)₄ and Gd_1−xTb_xCa₃(GaO)₃(BO₃)₄, were synthesized by conventional solid-state reactions. The crystalline phases of the resulting powders were identified using an X-ray diffraction system. Their photoluminescence properties were investigated under long-wavelength UV excitation. The Eu³⁺-doped and Tb³⁺-doped GdCa₃(GaO)₃(BO₃)₄ phosphors efficiently emitted red and green light, respectively. The temperature dependency of emission intensity was measured in a range from room temperature to 150 °C. The emission intensities of the red and green phosphors at 150 °C are 87% and 91% of those at room temperature, respectively. In addition, the decay times of both the red and green phosphors are shorter than 3 ms.     

Luminescence properties of Ca4Y6(SiO4)6O:RE (RE = Eu, Tb, Dy, Sm and Tm) under vacuum ultraviolet excitation

The vacuum ultraviolet excited luminescent properties of Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺ and Tm³⁺ in the matrices of Ca₄Y₆(SiO₄)₆O were investigated. The bands at about 173 nm in the vacuum ultraviolet excited spectra were attributed to host lattice absorption of the matrix Ca₄Y₆(SiO₄)₆O. For Eu³⁺-doped samples, the O²⁻ → Eu³⁺ CTB was identified at 258 nm. Typical 4f-5d absorption bands in the region of 195-300 nm were observed in Tb³⁺-doped samples. For Dy³⁺-doped and Sm³⁺-doped samples, the broad excitation bands consisted of host absorptions, CTB and f-d transition. For Tm³⁺-doped samples, the O²⁻ → Tm³⁺ CTB was located at 191 nm. About the color purity and emission intensity, Ca₄Y₆(SiO₄)₆O:Tb³⁺ is an attractive candidate of green light PDP phosphor, and Ca₄Y₆(SiO₄)₆O:Dy³⁺ has potential application in the field of mercury-free lamps.     

Polyspectral white light emission from Eu3+, Tb3+, Dy3+, Tm3+ co-doped GdAl3(BO3)4 phosphors obtained by combustion synthesis

Polycrystalline sub-micron-sized GdAl₃(BO₃)₄ phosphors co-doped with Eu³⁺, Tb³⁺, Dy³⁺ and Tm³⁺ have been prepared by combustion synthesis with urea. The phosphors have been characterised by X-ray diffraction, scanning electron microscopy, excitation and emission spectroscopy. The chromaticity co-ordinates and the colour temperatures of the fluorescence of the materials presented have been calculated and analysed with Commission Internationale l’Eclairage (CIE) programs and diagrams. Depending on the excitation wavelength, different colour temperatures of the light emitted can be achieved. Due to its polyspectral nature, the emitted light reveals a high colour rendering index.     

Solvothermal synthesis of SrMoO4:Ln (Ln = Eu, Tb, Dy) nanoparticles and its photoluminescence properties at room temperature

Rare-earth ions (Eu³⁺, Tb³⁺, Dy³⁺) doped SrMoO₄ nanoparticles were prepared by solvothermal route using oleic acid as surfactant to control the particle shape and size. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), photoluminescence spectra (PL) and the kinetic decay times were applied to characterize the obtained samples. The XRD patterns reveal that all the doped samples are assigned to the scheelite-type tetragonal structure of SrMoO₄ phase. In addition, the as-synthesized SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) particles are high purity well crystallized and with the average size of 30-50 nm. The possible formation process of SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) nanoparticles have been discussed as well. Upon excitation by ultraviolet radiation, the as-synthesized SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) nanoparticles exhibit the characteristic emission lines of corresponding Eu³⁺, Tb³⁺, Dy³⁺, respectively.     

The VUV–vis spectroscopic properties of phosphors Ca3Gd2(1−x)Ln2x(BO3)4 (Ln3+ = Ce,Sm, Eu,Tb)

The spectroscopic properties in VUV–vis range for phosphors calcium and gadolinium double borate Ca₃Gd₂(BO₃)₄ doped with rare-earth ions Ce³⁺, Sm³⁺, Eu³⁺ and Tb³⁺ were investigated. The host-related absorption, the f–d transitions of Ce³⁺ and Tb³⁺, as well as the charge transfer transitions of Sm³⁺ and Eu³⁺ in the host lattice are assigned and discussed. The CIE chromaticity coordinates for Eu³⁺- and Tb³⁺-activated phosphors are calculated.     

Vacuum ultraviolet excited photoluminescence properties of novel Na3Y9O3(BO3)8:Eu phosphor

The novel vacuum ultraviolet (VUV) excited Na₃Y₉O₃(BO₃)₈:Eu³⁺ red phosphor was synthesized and the photoluminescence (PL) properties were investigated. The phosphor showed strong VUV PL intensity, large quenching concentration (40 mol%) and good chromaticity (0.649, 0.351). The Eu³⁺-O²⁻ charge transition (CT) was observed to be at a higher energy (232 nm, 5.35 eV). The host absorption at 127-166 nm was broad and strong when monitoring the Eu³⁺ emission, which indicated that energy transfer from the host-lattice to the Eu³⁺ ions was efficient in Na₃Y₉O₃(BO₃)₈:Eu³⁺. These excellent VUV PL properties were revealed to be correlated with the unique isolated layer-type structure of Na₃Y₉O₃(BO₃)₈ host. The results showed that the Na₃Y₉O₃(BO₃)₈:Eu³⁺ would be a good candidate for VUV-excited red phosphor.     

Preparation, structure and luminescent properties of a new potassium yttrium borate K3Y3(BO3)4

A new yttrium borate compound K₃Y₃(BO₃)₄ has been obtained in the K₂O-Y₂O₃-B₂O₃ ternary system. Its structure, determined from single crystal X-ray diffraction data, shows that it belongs to space group P2₁/c with unit cell dimensions of a = 10.4667(16) Å, b = 17.361(3) Å, c = 13.781(2) Å and β = 110.548(8)°. The structure consists sheets of [Y₈B₈O₂₄]_∞ linked by out of sheet BO₃ groups and Y ions to form a three-dimensional framework. The luminescent properties of Eu³⁺ and Tb³⁺ doped K₃Y₃(BO₃)₄ materials have also been studied.     

Luminescence properties and energy transfer of a novel bluish-green tunable NaBa4(BO3)3:Ce3+, Tb3+ phosphor

A series of single-phased emission tunable NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ phosphors were synthesized by solid-state reaction. The crystal structure, photoluminescence properties, concentration quenching and energy transfer of NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ were systematically investigated. The wavelength-tunable bluish-green light can be realized by coupling the emission bands centered at 425 and 543 nm ascribed to the contribution from Ce³⁺ and Tb³⁺, respectively. The energy transfer from Ce³⁺ to Tb³⁺ in NaBa₄(BO₃)₃ host was studied and demonstrated to be a resonant type via a dipole–dipole interaction mechanism. The energy transfer efficiency (Ce³⁺ → Tb³⁺) obtained by decay curves was consistent with the result calculated by the emission intensity, which gradually increased from 0% to 84.5% by increasing the Tb³⁺ doping content from 0 to 0.45. The results indicate that the NaBa₄(BO₃)₃:Ce³⁺, Tb³⁺ phosphors have potential applications as an ultraviolet-convertible phosphor due to its effective excitation in the ultraviolet rang.     

Splitting and broadening of the emission bands of Y2O3:Eu3+,Nd3+ and its dependence on Nd3+ concentration and annealing temperature

Although Eu³⁺ ion-doped Y₂O₃ has been extensively used as red phosphors, their color rendering needs to be improved for high-quality illumination and displaying. Here, we show that the emission spectra of Y₂O₃:Eu³⁺ red phosphors can be broadened by the doping of Nd³⁺ ion so that the color rendering capability of Y₂O₃:Eu³⁺ was remarkably enhanced. Y₂O₃:Eu³⁺ and Y₂O₃:Eu³⁺,Nd³⁺ colloidal spheres were synthesized by wet chemical procedure and high-temperature treatment. The fluorescence measurement under the 254 and 380 nm ultraviolet excitation indicates that the 612 nm red emission peak of Eu³⁺ can be splitted into two ones by the doping of Nd³⁺ ion, of which the full width at half maximum (FWHM) is broadened from 4.2 nm to 9.6 nm. By varying the concentration of Nd³⁺ ion, it was determined that the optimal doping concentration of Nd³⁺ ion is of 3 mol% for realizing the strongest emission intensity. The further increase of Nd³⁺ ion exceeding 3 mol% would lead to a concentration quenching phenomenon. The analysis based on XRD spectra and the simplified energy diagram suggested that the doped Nd³⁺ ion not only monitored the growth dynamics, but also took an efficient energy transfer and a cross relaxation process to generate intense emission from Eu³⁺ ion in both of C₂ and S₆ sites, instead of preferable one type of Eu³⁺ site (C₂ or S₆) in the Nd³⁺ undoped sample.     

White-emitting phosphors Ca6La2Na2(PO4)6F2:Dy and luminescence enhancement through Ce → Dy energy transfer

Ce³⁺ and Dy³⁺ activated fluoro-apatite Ca₆La₂Na₂(PO₄)₆F₂ with chemical formulas Ca₆La_2−xLn_xNa₂(PO₄)₆F₂ (Ln = Ce³⁺, Dy³⁺) were prepared by a solid state reaction technique at high temperature. The vacuum-ultraviolet (VUV) and ultraviolet (UV) spectroscopic properties are investigated. The results indicate that Ce³⁺ ions show the lowest 5d excitation band at ∼305 nm and a broad emission band centered at ∼345 nm. Dy³⁺ ions exhibit intense absorption at VUV and UV range. White-emitting under 172 nm excitation is obtained based on two dominant emissions from Dy³⁺ ions centered at 480 and 577 nm. In addition, the energy transfer from Ce³⁺ to Dy³⁺ in the co-doped samples are observed and discussed.     

VUV–UV spectroscopic properties of RE (RE = Ce, Eu and Tb)-doped KMLn(PO4)2 (M = Ca, Sr; Ln = Y, La, Lu)

The VUV excited luminescent properties of Ce³⁺, Eu³⁺ and Tb³⁺ in the matrices of KMLn(PO₄)₂ (M²⁺ = Ca, Sr; Ln³⁺ = Y, La, Lu) were investigated. The bands at about 155 nm in the VUV–UV excitation spectra are attributed to the host lattice absorption, which indicates that the optical band gap of KMLn(PO₄)₂ is about 8.0 eV. Ce³⁺-doped samples show typical Ce³⁺ emission in the range of 300–450 nm, and the energy transfer from host lattice to Ce³⁺ is efficient. For Eu³⁺-doped samples, the O²⁻–Eu³⁺ CTBs are observed to be at about 228 nm except KSrLu(PO₄)₂:Eu³⁺ (247 nm). As for Tb³⁺-doped samples, typical 4f → 5d absorption bands in the region of 175–250 nm were observed.     

Influence of excitation wavelengths on luminescent properties of Sr3Al2O6:Eu, Dy phosphors prepared by sol-gel-combustion processing

Eu²⁺ and Dy³⁺ ion co-doped Sr₃Al₂O₆ red-emitting long afterglow phosphor was synthesized by sol-gel-combustion methods using Sr(NO₃)₂, Al(NO₃)₃·9H₂O, Eu₂O₃, Dy₂O₃, H₃BO₃ and C₆H₈O₇·H₂O as raw materials. The crystalline structure of the phosphors were characterized by X-ray diffraction, luminescent properties of phosphors were analyzed by fluorescence spectrophotometer. The effect of excitation wavelengths on the luminescent properties of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors was discussed. The emission peak of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor lays at 516 nm under the excitation of 360 nm, and at 612 nm under the excitation of 468 nm. The results reveal that the Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor will emit a yellow-green light upon UV illumination, and a bright red light upon visible light illumination. The emission mechanism was discussed according to the effect of nephelauxetic and crystal field on the 4f⁶5d¹ → 4f⁷ transition of the Eu²⁺ ions in Sr₃Al₂O₆. The afterglow time of (Sr_0.94Eu_0.03Dy_0.03)₃ Al₂O₆ phosphors lasts for over 600s after the excited source was cut off.     

Thermoluminescence properties of Ce-doped LiSr4(BO3)3 phosphor

Borates LiSr₄(BO₃)₃ were synthesized by high-temperature solid-state reaction. The thermoluminescence (TL) and some of the dosimetric characteristics of Ce³⁺-activated LiSr₄(BO₃)₃ were reported. The TL glow curve is composed of only one peak located at about 209 °C between room temperature and 500 °C. The optimum Ce³⁺ concentration is 1 mol% to obtain the highest TL intensity. The TL kinetic parameters of LiSr₄(BO₃)₃:0.01Ce³⁺ were studied by the peak shape method. The TL dose response is linear in the protection dose ranging from 1 mGy to 1 Gy. The three-dimensional thermoluminescence emission spectra were also studied, peaking at 441 and 474 nm due to the characteristic transition of Ce³⁺.     

The blue-light emission enhancement mechanism of Eu in Eu, Dy: SiO2 matrix

A Eu, Dy co-doped SiO₂ matrix xerogel with blue emission was prepared by the sol–gel method. Strong blue emission located between 425 nm and 525 nm with a peak at 486 nm is observed under UV laser excitation at room temperature, which is related to a 4f → 5d energy transition of Eu²⁺. Such techniques as FT-IR and TGA–DSC were used to measure the microstructure of the luminescent materials. The influence of Dy³⁺ ions on the luminescent property of Eu²⁺ was investigated. The emission intensity of Eu, Dy-codoped samples is stronger than that of Eu doped samples. The emission enhancement mechanism relating to Eu²⁺ is attributed to an energy transfer involving Dy³⁺ → Eu²⁺. Using energy transition theory, we speculate that the mechanism may be one of the resonance transfers via multi-polar interactions, and present a possible energy transfer model. The Eu²⁺ blue emission intensity reaches the maximum when the Dy³⁺ concentration is 0.1 mol%. When the concentration of Dy³⁺ is 0.3 mol%, a fluorescence quenching appears which might be related to the overlap part of Eu²⁺ excitation and emission levels, and also suggests the existence of Eu²⁺ → Eu²⁺ energy transfer.     

The Ce3+ → Tb3+ transfer in phosphate host lattices

A Ce³⁺ → Tb³⁺ transfer has been shown to appear in various phosphates belonging to different structural types and particularly in some new compounds: Na₃Ln(PO₄)₂:Ce, Tb; Na_xSr_3?2xLn_x(PO₄)₂:Ce, Tb and KCaLn(PO₄)₂:Ce, Tb.The presence of [PO₄ groups, in which the P-O bonds are strongly covalent, leads to a relatively weak crystal field at the rare-earth sites. The best overlapping between cerium emission and terbium excitation spectra is obtained for phosphates containing alkali ions. This result can be explained by a lowering of the emitting level of the cerium 5d configuration due to stronger covalency of the CeO bond and to an increasing crystal field at the rare-earth sites.     

Luminescence and Optical-Memory model of SrAl2O4:Eu2+,Dy3+ and Sr4Al14O25:Eu2+,Dy3+

The photoluminescence, luminescence excitation, and phosphorescence spectra of SrAl²O⁴:Eu²⁺,Dy³⁺ and Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ powder phosphors have been studied in detail at 80 and 300 K. A conceptual model is proposed for strontium-aluminate-based optical memory.     

Persistent luminescence of SrAl2O4: Eu,Dy, Cr phosphors in the tissue transparency window

We report on the persistent luminescence of SrAl₂O₄: Eu²⁺, Cr³⁺ phosphor centered at 760 nm. The phosphor was prepared by sol-gel-combustion method. Persistent luminescence from Cr³⁺ lasted for hundreds of seconds, comparable to the long afterglow from Eu²⁺ ions in the visible region based on the continuous energy transfer from Eu²⁺ ions to Cr³⁺ ions. The introduction of Dy³⁺ ions into the phosphor further prolonged the afterglow time of Eu²⁺ and Cr³⁺ ions through the depth control of the charge traps. The optimum doping concentrations for Eu²⁺, Cr³⁺ and Dy³⁺ were 1%, 2% and 1.5%, respectively.     

Photoluminescence properties of Sr3(PO4)2: Eu2+, Dy3+ double-emitting blue phosphor for white LEDs

Double-emitting blue phosphor Sr₃(PO₄)₂: Eu²⁺, Dy³⁺ was synthesized by solid state reaction under H₂ atmosphere. XRD exhibited the pure hexagonal phase of the prepared phosphor. The photoluminescence results showed that all samples had intense broad absorption band between 250 and 450 nm, which matched well with the near-UV (350–420 nm) emission band of InGaN-based chips. The emission spectrum of Sr₃(PO₄)₂: Eu²⁺, Dy³⁺ consisted of two broad bands, peaked at 485 nm and 410 nm, which originated from two luminescent centers, related to 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ in six-coordinated Sr(I) and ten-coordinated Sr(II) sites respectively. The intensity ratio of two emission bands could be easily tuned by adjusting Dy³⁺ co-doping content, which resulted in color-tunable luminescence in bluish green region to purplish blue region.     

Properties of Gd2O3:Eu, Tb nanopowders obtained by sol-gel process

A significant practical application for nanostructured materials is X-ray medical imagery, because it is necessary to use dense materials in order to enable absorption of high energy photons. An important requirement of these materials is UV-vis range emission produced by X-ray excitation, which can be influenced by the particle size. Europium doped gadolinium oxide is a well known red phosphor. Moreover, nanophosphors of Gd₂O₃ codoped with Tb³⁺, Eu³⁺ increase their light yield by energy transfer between Tb³⁺ and Eu³⁺. In this study, Gd₂O₃ nanopowders codoped with Eu³⁺ and Tb³⁺ (2.5 at.% Eu³⁺, and 0.005 and 0.01 at.% Tb³⁺) were obtained via a sol-gel process using gadolinium pentanedionate as precursor and europium and terbium nitrates as doping sources. In this paper, we report the influence of annealing temperature on the structure, morphology and luminescent properties of Gd₂O₃:Eu³⁺, Tb³⁺ by means of TGA, XRD, TEM and X-ray emission measurements.