Bifunctional application of La3BWO9:Bi3+,Sm3+ phosphors with strong orange-red emission and sensitive temperature sensing properties.

Through a solid-phase reaction technique, Sm3+ and Bi3+ co-doped La3BWO9 phosphors with high emission intensity and sensitive temperature sensing properties have been successfully synthesized. Based on XRD Rietveld refinement, the optimized crystal structure was used as the original model to calculate the band structure and partial density of states (PDOS) by density functional theory (DFT) calculations. The luminescence characteristics of Sm3+ and Bi3+ co-doped La3BWO9 phosphors were measured and analyzed. In addition, the optimal doping concentrations of Sm3+ and Bi3+ were investigated. The luminescence properties of Sm3+ doped phosphors were optimized by introducing Bi3+ ions. Efficient energy transfer from Bi3+ to Sm3+ ions was observed in La3BWO9:Sm3+, Bi3+ phosphors. An optical temperature sensor with high sensitivity was designed based on the different thermal quenching properties of Sm3+ and Bi3+ ions. In the temperature range of 293-498 K, the optimum absolute sensitivity (Sa) and maximum relative sensitivity (Sr) were 2.88 %K-1 and 1.32 %K-1, respectively. These results indicated that the prepared La3BWO9:Bi3+, Sm3+ phosphors have wide application prospects as solid state lighting materials and optical temperature sensors.

Infrared excited Er3+/Yb3+ codoped NaLaMgWO6 phosphors with intense green up-conversion luminescence and excellent temperature sensing performance.

The Er3+/Yb3+-codoped NaLaMgWO6 phosphors were synthesized via a traditional high-temperature solid-state reaction method. The temperature sensing performance was thoroughly investigated by studying the temperature-dependent up-conversion (UC) emission intensity ratio in the range of 293-533 K. A remarkable enhancement of green UC emission, as well as enhanced temperature sensitivity, were observed by increasing the Yb3+ concentration. The maximum absolute sensor sensitivity was 2.29% K-1 at 533 K. When the pump power of the 980 nm laser increased from 200 to 1000 mW, a slightly elevated temperature from 293-307 K was achieved in the compounds. Using the prepared phosphors and a 940 nm NIR chip, a green-emitting LED device was developed to confirm the applicability of our prepared phosphors for solid-state lighting. As a temperature probe, the prepared phosphor detected that the temperature increased from 286 K to 315 K when the drive current was increased from 90 mA to 300 mA. These results suggest that the Er3+/Yb3+-codoped NaLaMgWO6 phosphors have a potential application in solid-state lighting and optical thermometry.

Er3+-Activated NaLaMgWO6 double perovskite phosphors and their bifunctional application in solid-state lighting and non-contact optical thermometry.

Herein, Er3+-activated NaLaMgWO6 phosphors were prepared by a traditional high-temperature solid-state method. Based on the double perovskite structure of the NaLaMgWO6 host, we observe the desirable PL properties of Er3+. When excited at about 378 nm, the as-obtained materials can emit strong green light. When applied to a temperature sensor based on the fluorescence intensity ratio (FIR) principle, the prepared phosphors show excellent sensitivity ranging from 303 to 483 K. With elevated operation temperature, the sensitivity is about 2.23% K-1 at 483 K, resulting from the sensitive thermally coupled levels (2H11/2 and 4S3/2) of Er3+ ions in the double perovskite structure. The calculated relative sensitivity of the temperature sensor was 1.04% K-1 at 303 K. In particular, besides high sensitivity, its superior water resistance is an equally thrilling discovery. Therefore, it is demonstrated that the as-prepared Er3+-activated NaLaMgWO6 phosphors have promising potential applications in both near-UV solid-state lighting and non-contact optical thermometry.

Simultaneous bifunctional application of solid-state lighting and ratiometric optical thermometer based on double perovskite LiLaMgWO6:Er3+ thermochromic phosphors.

Realization of simultaneous, efficient bifunctional application of thermochromic phosphors on light emitting diodes (LEDs) and as ratiometric thermometers is significant. Herein, doped Er3+ ions are introduced as an activator into double perovskite LiLaMgWO6 host lattice. The developed phosphors can be efficiently excited by a near-ultraviolet LED chip and show bright green emission, mainly at 527 and 543 nm, as well as very low thermal quenching. Their chemical stability is studied, demonstrating excellent application potentials. Furthermore, the temperature sensing properties of LiLaMgWO6:0.01Er3+ were analyzed in the wide range of 303-483 K and show a good exponential relationship between ratiometric intensity and temperature (R 2 > 0.999), as well as high sensitivity (2.24% K-1). Such a system not only optimizes the performance in solid light emitting but also provides an excellent platform for designing high-sensitivity optical thermometry.

The Bond-Energy Method in Site Occupancy and Property of Eu3+ Doped in SrAl2B2O7 Phosphors.

The SrAl2B2O7:1%Eu3+ phosphors were obtained by solid-state reaction. Photoluminescence (PL) spectra are characterized the property of samples, and under the excitation of 394 nm, the sharp emission lines of SrAl2B2O7:1%Eu3+ can be assigned to Judd-Ofelt transitions (5D0-7FJ) of Eu3+, which are 5D0-7F1, 5D0-7F2, 5D0-7F3, and 5D0-7F4. The bond energy method is used to determine the site occupancy, and the occupancy of Eu3+ can be determined by comparing the deviation of its bond energy in different locations at Sr2+, Al3+ and B3+ sites. Theoretical calculation result indicates that Eu3+ would preferentially occupy the smaller energy variation sites Sr2+.

The Bond-Energy Method in Site Occupancy and Property of High Concentration Eu3+ in Sr2CeO4 Phosphors.

The low concentration of Eu3+ doped Sr2CeO4 phosphors has been widely studied in recent years and in this paper, we researched the properties of high concentration Eu3+ doped in Sr2CeO4. The Sr2Ce(1-x)Eu4-x/2 (x = 0, 1%, 10%, 20%) phosphors were obtained by traditional solid-state reaction. Photoluminescence (PL) spectra are characterized the property of samples. PL spectra illustrate that the concentration of Eu3+ increased, the intensity of 5D0-7F1, 5D0-7F2 increased and intensity of Sr2CeO4 host emission intensity was decreased. The phenomenon can be ascribed to the energy transfer from Ce4+ to Eu3+. When the concentration of Eu3+ is 20%, the completely red emission can be obtained even if no other ions are doped under the excitation wavelength of 350 nm, it is proved that Eu3+ occupied Ce sites rather than Sr site in Sr2CeO4 samples. The conclusion we make is due to the value of |ΔEEuCe-O| and |ΔEEuSr-O| calculated by bond-energy method, the smaller the value, the easier it is for the doped ions Eu3+ to enter the site.

Bond energy, site preferential occupancy and Eu2+/3+ co-doping system induced by Eu3+ self-reduction in Ca10M(PO4)7 (M = Li, Na, K) crystals.

Ca10M(PO4)7:Eu (M = Li, Na, K) phosphors have been synthesized via a solid-state reaction process, their phase purity was examined using XRD patterns, and Rietveld refinement confirmed that the Ca10Li(PO4)7, Ca10Na(PO4)7 and Ca10K(PO4)7 are pure phases. The photoluminescence properties of the Ca10M(PO4)7:Eu (M = Li, Na, K) phosphors showed that the self-reduction of Eu3+ to Eu2+ can occur in an air atmosphere. Eu3+ ions can be reduced to Eu2+ ions when doped in Ca10Li(PO4)7, Ca10Na(PO4)7 and Ca10K(PO4)7 crystals, which was detected using photoluminescence spectra. In this work, the bond energy method was used to determine and explain the mechanism of site occupation of Eu entering the host matrix. According to the calculated value of the deviation of bond energy for Eu3+-doped Ca10M(PO4)7 (M = Li, Na, K) crystals, the similar value between and , and , and and can provide the conditions for the self-reduction of Eu3+ in the Ca10M(PO4)7 (M = Li, Na, K) system. Meanwhile, the smaller deviation values of , , and in Ca10Li(PO4)7, Ca10Na(PO4)7, and Ca10K(PO4)7 crystals and in Ca10K(PO4)7 crystals indicated that the preferential sites of Eu ion occupancy in the Ca10M(PO4)7 (M = Li, Na, K) lattices are Li, Na, K and Ca sites. The conclusions obtained from the calculated results of the bond energy method are consistent with the Rietveld refinement and the photoluminescence spectra of Ca10M(PO4)7 (M = Li, Na, K).

Break the Interacting Bridge between Eu3+ Ions in the 3D Network Structure of CdMoO4: Eu3+ Bright Red Emission Phosphor.

Eu3+ doped CdMoO4 super red emission phosphors with charge compensation were prepared by the traditional high temperature solid-state reaction method in air atmosphere. The interrelationships between photoluminescence properties and crystalline environments were investigated in detail. The 3D network structure which composed by CdO8 and MoO4 polyhedra can collect and efficiently transmit energy to Eu3+ luminescent centers. The relative distance between Eu3+ ions decreased and energy interaction increased sharply with the appearance of interstitial occupation of O2- ions ([Formula: see text]). Therefore, fluorescence quenching occurs at the low concentration of Eu3+ ions in the 3D network structure. Fortunately, the charge compensator will reduce the concentration of [Formula: see text] which can break the energetic interaction between Eu3+ ions. The mechanism of different charge compensators has been studied in detail. The strong excitation band situated at ultraviolet and near-ultraviolet region makes it a potential red phosphor candidate for n-UV based LED.

Eu3+/2+ co-doping system induced by adjusting Al/Y ratio in Eu doped CaYAlO4: preparation, bond energy, site preference and 5D0-7F4 transition intensity.

CaY1-x Al1+x O4:2%Eu (x = 0, 0.1, 0.2) phosphors have been synthesized via a solid-state reaction process. XRD patterns indicate that they are pure phase. The photoluminescence properties of the CaY1-x Al1+x O4:2%Eu phosphors exhibit both the blue emission of Eu2+ (4f65d1-4f7) and red-orange emission of Eu3+ (5D0-7F1,2,3,4) under UV light excitation, which showed that the Eu3+/2+ co-doping system was obtained by adjusting the Al/Y ratio. Eu3+ ions can be reduced to Eu2+ ions when the Al/Y ratio was changed. In this work, the bond energy method was used to determine and explain the mechanism of the site occupation of Eu ions entering the host matrix. Also, the emission spectrum showed an unusual comparable intensity 5D0-7F4 transition peak. The relative intensity of 5D0-7F2 and 5D0-7F4 can be stabilized by changing the relative proportions of Al3+ and Y3+. Furthermore, this was explained by the J-O theory.

Preferential occupancy of Eu3+ and energy transfer in Eu3+ doped Sr2V2O7, Sr9Gd(VO4)7 and Sr2V2O7/Sr9Gd(VO4)7 phosphors.

The vanadate-based phosphors Sr2V2O7:Eu3+ (SV:Eu3+), Sr9Gd(VO4)7:Eu3+ (SGV:Eu3+) and Sr9Gd(VO4)7/Sr2V2O7:Eu3+ (SGV/SV:Eu3+) were obtained by solid-state reaction. The bond-energy method was used to investigate the site occupancy preference of Eu3+ based on the bond valence model. By comparing the change of bond energy when the Eu3+ ions are incorporated into the different Sr, V or Gd sites, we observed that Eu3+ doped in SV, SGV or SV/SGV would preferentially occupy the smaller energy variation sites, i.e., Sr4, Gd and Gd sites, respectively. The crystal structures of SGV and SV, the photoluminescence properties of SGV:Eu3+, SV, SGV/SV and SGV/SV:Eu, as well as their possible energy transfer mechanisms are proposed. Interesting tunable colours (including warm-white emission) of SGV/SV:Eu3+ can be obtained through changing the concentration of Eu3+ or changing the relative quantities of SGV to SV by increasing the calcination temperature. Its excitation bands consist of two types of O2- → V5+ charge transfer (CT) bands with the peaks at about 325 and 350 nm respectively, as well as f-f transitions of Eu3+. The obtained warm-white emission consists of a broad photoluminescence band centred at about 530 nm, which originates from the O2- → V5+ CT of SV, and a sharp characteristic spectrum (5D0-7F2) at about 615 and 621 nm.

Preparation and Luminescent Properties of Sm3+-Doped High Thermal Stable Sodium Yttrium Orthosilicate Phosphor.

Orange-red-emitting sodium yttrium orthosilicate NaYSiO4:xSm3+ (x = 0.005, 0.01, 0.02, 0.05, 0.10, 0.15, and 0.20) were synthesized. The phase structure and photoluminescence properties of these phosphors were investigated. The emission spectrum obtained by excitation into 406 nm contains exclusively the characteristic emissions of Sm3+ at 571 nm, 602 nm, 648 nm, and 710 nm, which correspond to the transitions from 4G5/2 to 6H5/2, 6H7/2, 6H9/2, and 6H11/2 of Sm3+, respectively. The strongest one is located at 602 nm due to the 4G5/2 --> 6H7/2 transition of Sm3+, generating bright orange-red light. The optimum dopant concentration of Sm3+ ions in NaYSiO4:xSm3+ is around 2 mol%, and the critical transfer distance of Sm3+ is calculated as 23 Å. The thermal quenching temperature is above 500 K. The fluorescence lifetime of Sm3+ in NaYSiO4:0.02Sm3+ is 1.83 ms. The NaYSiO4:Sm3+ phosphors may be potentially used as red phosphors for white light emitting diodes.

Citrate-Complexation Synthesis and Photoluminescence Properties of Y6MoO12:Eu Nanocrystalline.

Y6MoO12 doped with Eu3+ was synthesized using a citrate-complexation route, and was calcined at 800 °C and 1400 °C, respectively. The structure, morphology and photoluminescence (PL) properties of the samples, and their dependence on the crystallite size were investigated. XRD patterns indicate that the Y6MoO12:Eu3+ powder was obtained at both calcination temperatures, and had a cubic structure. The results also suggest that Y6MoO12:Eu3+ calcined at 800 °C was in the nanocrystalline phase, which was confirmed by the SEM microimage. The crystalline size was about 140 nm. Both phosphors could be excited via three channels: f-f excitation of Eu3+ by blue light, MoO groups excitation by near-UV light, and charge transfer state excitation of Eu3+ by UV light. Both samples yielded red light emissions dominated by the 5D0-7F2 transition at 613 nm. The excitation efficient of the three channels depended on the calcination temperature. The energy transfer from the MoO groups to the Eu3+ ions was more effective in the nanocrystalline phase. The temporal decay feature of the phosphor was also characterized.

Elaboration, Structure and Luminescence of Sphere-Like CaF2:RE Sub-Microparticles by Ionic Liquids Based Hydrothermal Process.

A new and simple method for the synthesis of rare earth ion doped CaF2 (CaF2:RE³âº) sub- microparticles is presented, using an ionic liquids based hydrothermal process. The structural properties of the CaF2 nanoparticles were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The CaF2 nanoparticles exhibited a sphere-like morphology with a diameter of about 150 nm. During the synthesis, the ionic liquid [bmim]BF4(1-butyl, 2-methylimidazolium tetrafluoroborate) acts as both a co-solvent and reactant. The crucial effect of EDTA-2Na (ethylene diamine tetra acetic acid disodium salt) on the formation of CaF2:RE sub-microparticles was explored and discussed. The strong green (513-569 nm) and strong red (636-685 nm) upconversion emissions of the CaF2:Er³âº, Yb³âº nanoparticles (λex = 980 nm) were also investigated. The luminescent properties of CaF2:Eu³âº and CaF2:Ce³âº,Tb³âº were also evaluated. This work may represent a new step in synthesizing fluoride sub-nanocrystals using ionic liquids.

Ce(3+) /Tb(3+) non-/single-/co-doped K-Lu-F materials: synthesis, optical properties, and energy transfer.

Using a hydrothermal method, Ce(3+) /Tb(3+) non-/single-/co-doped K-Lu-F materials have been synthesized. The X-ray diffraction (XRD) results suggest that the Ce(3+) and/or Tb(3+) doping had great effects on the crystalline phases of the final samples. The field emission scanning electron microscopy (FE-SEM) images indicated that the samples were in hexagonal disk or polyhedron morphologies in addition to some nanoparticles, which also indicated that the doping also had great effects on the sizes and the morphologies of the samples. The energy-dispersive spectroscopy (EDS) patterns illustrated the constituents of different samples. The enhanced emissions of Tb(3+) were observed in the Ce(3+) /Tb(3+) co-doped K-Lu-F materials. The energy transfer (ET) efficiency ηT were calculated based on the fluorescence yield. The ET mechanism from Ce(3+) to Tb(3+) was confirmed to be the dipole-quadrupole interaction inferred from the theoretical analysis and the experimental data. Copyright © 2015 John Wiley & Sons, Ltd.

Synthesis and Photoluminescent Properties of Nanorod Bundle Ln4O(OH)9NO3:Eu(Ln = Y, Lu) Prepared by Hydrothermal Method.

Well-crystallized nanorod bundles Ln4O(OH)9NO3:1%Eu(Ln = Y, Lu) have been successfully prepared by hydrothermal method. The crystalline phase, size and optical properties were characterized using powder X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), infrared (IR) spectrograph and photoluminescent (PL) spectra. Site occupations of Eu3+ in crystals Ln4O(OH)9NO3:Eu(Ln = Y, Lu) were discussed based on excitation spectra and the empirical relationship formula between the charge transfer (CT) energy and the environmental factor. The emission spectra exhibited that the strongest emission peaks with an excitation wavelength of 395 nm were at 617 and 626 nm in crystal Lu4O(OH)9NO3:1%Eu and Y4O(OH)9NO3:1%Eu, respectively, both of which come from 5D0-7F2 transition of the Eu3+ ions. The broad excitation peaks at about 254 and 255 nm were found when monitored at 617 and 628 nm in crystal Lu4O(OH)9NO3:1%Eu and Y4O(OH)9NO3:1%Eu, respectively, which were due to O-Eu CT transition. Based on the dielectric theory of complex crystal, the CT bands at about 254 and 255 nm in Ln4O(OH)9NO3:1%Eu(Ln = Y, Lu) were assigned to the transition of O-Eu at Ln3(Ln = Y, Lu) site, from which we can conclude that Eu3+ ions occupied the site of Ln3(Ln = Y, Lu) in crystal Ln4O(OH)9NO3:1%Eu(Ln = Y, Lu). It put forward a new route to investigate site occupation of luminescent center ions in rare earth doped complex inorganic luminescence materials.

Synthesis and Luminescent Properties of Eu(3+) Doped CaGd4O7 Phosphors by Solvothermal Reaction Method.

Eu(3+) doped CaGd4O7 phosphors have been newly synthesized using a solvothermal reaction method and sintered at 1400 °C. The phase, composition, morphologies, and photoluminescent properties of the phosphors have been well characterized by means of the X-ray diffraction (XRD) patterns, energy dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FE-SEM), photoluminescence (PL) spectroscopy, and decay curves, respectively. The XRD patterns of the as-prepared phosphors confirm their monoclinic structure and the FE-SEM images reveal flower-like morphology, formed through agglomeration. The calculated size of the crystallites was approximately 83 nm. The photoluminescence excitation (PLE) spectra of CaGd4O7:Eu(3+) phosphors consist of a broad band due to the charge transfer (CT) electronic transition, and several sharp peaks that can be attributed to the f-f transitions of Eu(3+) and Gd(3+). The PL spectra exhibited a stronger red emission corresponding to the (5)D0 --> (7)F2 transition. The CIE chromaticity coordinates of the phosphors were calculated and all the chromaticity coordinates have been placed in the red spectral region. These luminescent powders are expected to have potential applications for white light-emitting diodes (WLEDs) and optical display systems.

Synthesis, phase evolution and optical properties of Tb(3+)-doped KF-YbF3 system materials.

KF-YbF3 system materials have been synthesized by a hydrothermal method without any surfactant or template. By controlling the reactant ratios of KF:Yb(3+), the hydrothermal temperature and the pH of the prepared solutions, the final products can evolve among the orthorhombic phase of YbF3, the cubic phase of KYb3F10 and the cubic phase of KYbF4. The X-ray diffraction (XRD) patterns of the samples prove the phase evolution of the final products. The morphologies of the samples were characterized using field emission scanning electron microscopy (FE-SEM) images and the evolution of the morphology is consistent with that of the crystalline phases. The optical properties of Tb(3+) in the samples were characterized by PL excitation and emission spectra, as well as luminescent decay curves.

Simultaneous realization of two approaches to white light in single-component phosphors.

A novel single-component warm white light-emitting Sr(2)Ca(0.995)MoO(6): Sm(3+) (0.005) phosphor was synthesized by solid-state reaction. The photoluminescence excitation spectra ranging from 300 to 450 nm and 460 to 500 nm broadly are observed. Direct full-color warm white light [(x, y) = 0.3221, 0.3525] was realized in this single-phase phosphor with exposure to 380 nm UV light. When this phosphor is pumped by 466 nm radiation we obtained yellow emission with an intense red component, suggesting that this material is also competitive as a blue-pumped yellow phosphor. Thus two approaches to white light are realized simultaneously in Sm(3+) doped single-component phosphor for the first time. The quantum yield and the reliability of the as-synthesized phosphors for White LED applications were also investigated.

Synthesis, optical properties, and energy transfer of Ce(3+)/Tb(3+) co-doped MyGdFx (M=Li, Na, K).

Through a solid-state reaction method, the Ce(3+)/Tb(3+) co-doped MyGdFx (M=Li, Na, K; x=3, 4, 6; y=0, 1, 3) system samples have been synthesized by controlling the annealing temperatures and the ratios of raw materials. The samples were characterized by X-ray diffraction (XRD) patterns, photoluminescence (PL) excitation and emission spectra as well as luminescent dynamic decay curves. The experimental results suggest that the LiF is more difficult to react with the prepared material compared that of NaF or KF under similar reaction conditions. The samples crystallized in different crystalline phases. The energy transfer from Ce(3+) to Tb(3+) or Ce(3+) to Gd(3+) to Tb(3+) has been observed in all the samples. The Ce(3+) and Tb(3+) present different optical properties for they are sensitive to the local environment. In addition, the deduced lifetime of Tb(3+)(5)D4→(7)F5 transition decreases in the same system samples with the annealing temperature increasing. The deduced lifetime of Tb(3+)(5)D4→(7)F5 also decreases with the increase of the KF concentration in the KF system samples.

Chemical bond properties and charge transfer bands of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) in Eu(3+)-doped garnet hosts Ln3M5O12 and ABO4 molybdate and tungstate phosphors.

Charge transfer (CT) energy from the ligand to the central ions is an important factor in luminescence properties for rare earth doped inorganic phosphors. The dielectric theory of complex crystals was used to calculate chemical bond properties. Combining the photoluminescence and the dielectric theory of complex crystals, the CT bands of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) for Eu(3+)-doped inorganic phosphors have been investigated experimentally and theoretically. Taking Eu(3+)-doped Ln3M5O12 (Ln = Y, Lu and M = Al, Ga), Gd3Ga5O12, MMoO4 (M = Ca, Sr, Ba) and MWO4 (M = Ca, Sr, Ba) as typical phosphors, we investigated the effects of the cation size on the CT bands and chemical bond properties including the bond length (d), the covalency (fc), the bond polarizability (αb) and the environmental factor (he) of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+), respectively. For systematic isostructural Ln3M5O12 (Ln = Y, Lu and M = Al, Ga) phosphors, with the increasing M ion radius, the bond length of Ln-O decreases, but fc and αb increase, which is the main reason that the environmental factor increased. For the isostructural MMoO4:Eu, with the increasing M ion radius, the Mo-O bond length increases, but fc and αb decrease, and thus he decreases. However, in the compound system MWO4:Eu (M = Ca, Ba) with the increasing M ion radius, the O-W bond length increases, but fc and αb increase, and thus he increases and the O-W CT energy decreases. Their O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) CT bands as well as their full width at half maximum (FWHM) were directly influenced by he. And with the increasing he, CT bands of O-Eu or O-Mo or O-W decrease and their FWHM increases. These results indicate a promising approach for changing the material properties, searching for new Eu(3+) doped molybdate, tungstate or other oxide phosphors and analyzing the experimental result.