Photoluminescence and optical temperature sensing in Sm3+-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 lead-free ceramics

A series of orange-red emitting Sm³⁺ activated Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ (BCZT: xSm³⁺, x?=?0.001–0.007) are synthesized by a conventional solid-state reaction method. The Sm³⁺ ions composition dependent photoluminescence properties are systematically investigated. Under the excitation of a 407?nm near-ultraviolet light, the ceramics exhibit strong characteristic emission of Sm³⁺ ions with dominant orange-red emission peak at around 595?nm, which is ascribed to the transition of ⁴G_5/2 → ⁶H_7/2. The BCZT: 0.004Sm³⁺ ceramic displays the optimal emission among these Sm³⁺-doped BCZT solid solutions. Moreover, the photoluminescence intensity exhibits extremely sensitive to temperature, suggesting that BCZT: 0.004Sm³⁺ could be applicable for temperature sensing. A maximum relative sensitivity of 1.89%?K^?1 at 453?K is obtained. Furthermore, the existence of ferroelectricity in the BCZT host combined with Sm³⁺ activated photoluminescence properties could be useful for developing optical-electro multifunctional materials and devices.     

Sol-gel synthesis and luminescence properties of Ba2SiO4:Sm3+ nanostructured phosphors

Ba₂SiO₄:Sm³⁺ nanostructure phosphors have been synthesized by a simple sol-gel method. Phase evaluation, structural characteristics and photoluminescence properties of the synthesized Ba₂SiO₄:Sm³⁺ powders were studied using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy (PL). X-ray diffraction results showed that all synthesized samples were single-phase barium silicate (Ba₂SiO₄) and samarium (Sm) ions were incorporated into the lattice of Ba₂SiO₄. Adding samarium to barium silicate changed the microstructure from vermicular to spherical structures. The Photoluminescence spectrum of Ba₂SiO₄:Sm³⁺ phosphors exhibited characteristic emission peaks at 562?nm which is due to the ⁴G_{5/2 →}⁶H_7/2 transition of samarium ions and corresponds to the orange region. The results showed that the barium silicate activated with 0.08?mol samarium exhibited the highest PL intensity.     

LiCa3MgV3O12:Sm3+: A new high-efficiency white-emitting phosphor

A novel single-phased white-light-emitting phosphor Sm³⁺ doped LiCa₃MgV₃O₁₂ (LCMV) was developed. The LCMV host was one self-activated bluish-green emitting phosphor, which possessed an efficient excitation band in the 250–400?nm wavelength range and showed an intense broadband bluish-green emission with internal quantum efficiency (IQE) of 39%. Doping Sm³⁺ ions in to LCMV host induced tunable-color emissions, due to the energy transfer from [VO₄]^3? to Sm³⁺ ions. Importantly, under 340?nm excitation, the LCMV:Sm³⁺ can emitted bright white light by combining the self-activated luminescence of LCMV host and the red emissions of Sm³⁺ ions, and the IQE of the white-emitting composition-optimized LCMV:0.01Sm³⁺ phosphors reached up to 45%. These white-emitting LCMV:Sm³⁺ phosphors have potential applications in white light-emitting diodes and optical display devices.     

Synthesis and photoluminescent properties of high-efficient color-tunable Ba3Y2B6O15: Ce3+, Tb3+ phosphors

High-efficient Ce³⁺/Tb³⁺ co-doped Ba₃Y₂B₆O₁₅ phosphors with multi color-emitting were firstly prepared, and their structural and luminescent properties were studied by XRD Rietveld refinement, emission/excitation spectra, fluorescence lifetimes as well as temperature-variable emission spectra. Upon 365?nm excitation, the characteristic blue Ce³⁺ band along with green Tb³⁺ peaks were simultaneously found in the emission spectra. Moreover, by increasing concentration of Tb³⁺, a blue-to-green tunable emitting color could be realized by effective Ce³⁺→Tb³⁺ energy transfer. Furthermore, all Ba₃Y₂B₆O₁₅: Ce³⁺, Tb³⁺ phosphors exhibit high internal quantum efficiency of ~?90%, while the temperature-variable emission spectra reveal that the phosphors possess impressive color stability as well as good thermal stability (T₅₀ =?~?120?°C). The results indicate that these efficient color-tuning Ba₃Y₂B₆O₁₅: Ce³⁺, Tb³⁺ might be candidate as converted phosphor for UV-excited light-emitting diodes.     

Dazzling cool white light emission from Ce3+/Sm3+ activated LBZ glasses for W-LED applications

We synthesized a batch of co-doped (Ce³⁺+Sm³⁺): LBZ glass specimens by melt quenching process and their structural and radiation properties were studied by employing XRD, FE-SEM, optical absorption, photoluminescence and lifetime measurements. UV–Vis–NIR absorption studies of the co-doped (Ce³⁺+Sm³⁺): LBZ glassy matrix displays pertinent bands of both Ce³⁺ and Sm³⁺ ions. Individually doped Sm³⁺: LBZ glass exhibit bright orange emission at 603?nm (⁴G_5/2 → ⁶H_7/2) under the excitation of 403?nm. Nevertheless, the luminescence intensities pertaining to Sm³⁺ were extraordinarily increased by co-doping with Ce³⁺ ions to Sm³⁺: LBZ glassy matrices because of energy transfer from Ce³⁺ to Sm³⁺. The fluorescence spectra of co-doped (Ce³⁺+Sm³⁺): LBZ exhibits characteristic emission bands of Ce³⁺ (441?nm, blue) and Sm³⁺ (603?nm, reddish orange) under the excitation of 362?nm. Decay curves of Ce³⁺ and Sm³⁺ ions in co-doped glass has been fitted to double exponential nature. The decreasing lifetime of donor ion and rising lifetime of acceptor ion in double doped glass could support the energy transfer from Ce³⁺ to Sm³⁺ ions in the host matrix. The CIE coordinates and CCT values were calculated for all the obtained co-doped glassy samples from their luminescence spectra. By adding Ce³⁺ ions to individually doped Sm³⁺: LBZ glass matrix, the emitting color changes from reddish orange to white light which resembles the energy transfer from Ce³⁺ to Sm³⁺ ions. These studies, perhaps implied that attained co-doped (Ce³⁺+Sm³⁺): LBZ glassy samples are potential materials for white lighting appliances.     

Synthesis and spectroscopic analysis of Sm3+ doped CeO2 ceramic powders for the application of white LEDs

Orange-red light-emitting Sm³⁺-doped cerium oxide (CeO₂) ceramic powder with various concentrations of Sm³⁺ ions was prepared through a sol-gel process. X-ray diffraction and Rietveld analysis confirmed the formation of a purely cubic structure with a space group of $\mathit{Fm}\stackrel{?}{3}m$. The lattice parameters and unit cell volumes of the CeO₂:Sm³⁺ powder increased with the concentration of Sm³⁺ ions. The energy-dispersive X-ray spectra and corresponding mapping images confirmed the elemental composition and adequate dispersion of all elements in the CeO₂:Sm³⁺ powder. A broad excitation band at approximately 365?nm was observed in the excitation spectra of CeO₂:Sm³⁺ phosphors owing to the charge transfer transition from O 2p to Ce 4f orbitals. The Sm³⁺ doped CeO₂ phosphors emitted sharp luminescence with a main peak at 615?nm under excitation at 360?nm. The spectral analysis revealed that the CeO₂:Sm³⁺ phosphors exhibited strong orange-red emission. Concentration quenching was observed in the CeO₂:Sm³⁺ phosphors with 0.5?mol% of critical concentration of Sm³⁺ ions due to dipole dipole interaction of two nearest Sm³⁺ ions. The quantum efficiency was observed as high as 58%. The thermal stability of the present materials was estimated with the evaluation of activation energy as 0.31?eV. The broad excitation band and sharp orange–red emission indicated the potential use of CeO₂:Sm³⁺ phosphors for white light-emitting diodes.     

Photoluminescence properties of a double perovskite tungstate based red-emitting phosphor NaLaMgWO6:Sm3+

In this work, the conventional solid-state method was applied to synthesize a series of red-emitting NaLaMgWO₆:Sm³⁺ phosphors. The crystal structure, phase purity, morphology, particle size distribution as well as elemental composition of the as-prepared phosphors were investigated carefully with the aid of XRD, SEM, EDS, FT-IR analyses, indicating the high-purity and micron-sized NaLaMgWO₆:Sm³⁺ phosphors with monoclinic structure were prepared successfully. The spectroscopic properties of Sm³⁺ in NaLaMgWO₆ host including UV–vis diffuse reflection spectrum, photoluminescence excitation and emission spectra, decay curves, chromaticity coordinates and internal quantum efficiency were investigated in detail. Upon excitation with UV (290 nm) and n-UV (406 nm), NaLaMgWO₆:Sm³⁺ phosphor presented red emission corresponding to the ⁴G_5/2→⁶H_J (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm³⁺, in which the hypersensitive electronic dipole transition ⁴G_5/2→⁶H_9/2 (645 nm) was with the strongest emission intensity because Sm³⁺ ions were located at a lattice site with anti-inversion symmetry. The optimal concentration of Sm³⁺ was different for the given excitation wavelength such as 290 nm and 406 nm, which was interpreted by the extra effect of the energy transfer from W⁶⁺-O^2- group to Sm³⁺. The decay lifetime for ⁴G_5/2→⁶H_9/2 transition of Sm³⁺ was very short (< 1 ms) and decreased with the increasing Sm³⁺ concentration. The present investigation indicates that NaLaMgWO₆:Sm³⁺ phosphor could be a potential red component for application in w-LEDs.     

Greenish-yellow emitting CdS: Sm3+ nanoparticles: Structural and optical analysis

Different concentrations of trivalent samarium (Sm³⁺) ions doped cadmium sulphide (CdS) nanoparticles were fabricated by one-step solid-state method at low temperature using C₁₀H₆(SO₃Na)₂ as surfactant for optoelectronic and solar cell applications. They were characterized through powder X-ray diffraction, Fourier transform infrared, Raman, scanning electron microscopy, transmission electron microscopy, UV–Vis absorption and photoluminescence studies. These nanoparticles establish cubic structure without any foreign phase and it was confirmed by Raman studies. The Raman spectrum of CdS nanoparticles shows first three longitudinal optical phonon orders. The adjacent lattice fringes were spaced about 0.30 nm. The direct band gap energy was found slightly higher than the bulk crystallites. The photoluminescence spectra of CdS: Sm³⁺ exhibits a broad peak at 563 nm with a shoulder at around 607 nm corresponding to Sm³⁺: ⁴G_5/2 → ⁶H_7/2 transition at 402 nm excitation. A luminescence quenching was noticed at higher Sm³⁺ ions concentration due to transfer of energy among the excited Sm³⁺ ions. The CdS: Sm³⁺ particles were fabricated with a size of the order of nanoscale and they can be used for efficient energy conversion. The studied CdS: Sm³⁺ nanoparticles are suitable for optoelectronic and solar cell applications.     

Bismuth-activated,narrow-band,cyan garnet phosphor Ca3Y2Ge3O12:Bi3+ for near-ultraviolet-pumped white LED application

Herein, a novel Bi³⁺-activated Ca₃Y₂Ge₃O₁₂ (CYGO) narrow-band cyan-emitting phosphor was synthesized. It can be excited from 320–420 nm, and the strongest excitation peak is located at 370 nm, which is suitable for current near-ultraviolet (NUV) chips perfectly. The full width at half maximum is at 52 nm. By analyzing the crystal structure of the sample, we infer that the Bi³⁺ ions replace the Y³⁺ site to form a highly symmetrical BiO₆ octahedron. The time-resolved photoluminescence (TRPL) spectra of CYGO: Bi³⁺ reveal that the only a single emission center exists in the host lattice. A warm white light–emitting diode (WLED) device with a low correlated color temperature (3148 K) and a high color rendering index (90.2) was fabricated by using the as-prepared sample, and the significant thermal stability of CYGO: Bi³⁺ guarantees its potential application in WLEDs. It is verified that the structure with only one crystallographic Y site for Bi³⁺ dopant occupation and highly symmetrical and dense structure is conducive to realize narrow-band emission, which will provide experience for researchers to explore more Bi³⁺-activated phosphors used for high-end lighting.     

Luminescence properties of Sm3+ ions doped heavy metal oxide tellurite-tungstate-antimonate glasses

The trivalent Sm³⁺ ion doped tellurium-antimony-tungsten oxides based glasses were prepared by conventional melt quenching and pressing method. Spectroscopic characterizations such as optical absorption, photoluminescence and decay profile measurements were performed on the glasses. Judd-Ofelt theory is used to evaluate the oscillator strengths and the three phenomenological intensity parameters (Ω_λ, λ = 2, 4, 6) of the glasses. The photoluminescence spectra recorded under 479 nm excitation exhibited the emission bands at 562, 598, 645 and 708 nm corresponding to the transitions ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2, 11/2) respectively. Using J-O parameters (Ω_λ) various important radiative parameters viz., transition probabilities, emission cross-sections, branching ratios of various emission bands were evaluated. Decay profiles were recorded to find the lifetime of the ⁴G_5/2 excited level and the obtained life time values are observed to decrease with an increase of Sm³⁺ ion concentration; such decrease is attributed due to clustering of Sm³⁺ ions which may cause luminescence quenching.     

Samarium doped hafnium oxide cubic and monoclinic nanometric powders synthesized by hydrothermal route

Hafnium oxide nanoparticles doped with trivalent samarium (HfO₂:Sm³⁺) were synthesized by hydrothermal route from chloride reagents. Different samarium doping concentrations (0, 0.5, 1, 3, 5 and 10?at% with respect to Hf) and different post-annealing temperatures (200, 400, 600, 800 and 1000?°C) were evaluated. The resulting nanoparticles showed an oval morphology with average sizes below 30?nm. A sensitive relationship between the samarium concentration and the resulting crystal structure of the material was observed by X-Ray diffraction and further evidenced by the cathodoluminescence and photoluminescence spectra. Low concentrations of samarium (0, 0.5 and 1?at%) generated a monoclinic phase, whereas higher concentrations of samarium (5 and 10?at%) generated a metastable cubic phase. The average crystallite sizes calculated by the Scherrer's equation were close to 8?nm and 12?nm for cubic and monoclinic phases, respectively. The luminescent emission corresponded to the characteristic 4f-4f transitions of the samarium ion with a principal peak centered at 610?nm. The best luminescent properties were obtained with the sample doped with samarium at 0.5?at%, annealed at 600?°C.     

High luminescent brightness and thermal stability of red emitting Li3Ba2Y3(WO4)8:Eu3+ phosphor

A series of Li₃Ba₂Y_3−x(WO₄)₈:xEu³⁺ (x=0.1, 1, 1.5, 2 and 2.8) phosphors were synthesized by a high temperature solid-state reaction method. Under the excitation of near ultraviolet (NUV) light, the as-prepared phosphor exhibits intense red luminescence originating from the characteristic transitions of Eu³⁺ ions, which is 1.8 times as strong as the commercial Y₂O₂S:Eu³⁺ phosphor. The optimal doping concentration of Eu³⁺ ions here is confirmed as x=1.5. The electric dipole-quadrupole (D-Q) interaction is deduced to be responsible for concentration quenching of Eu³⁺ ions in the Li₃Ba₂Y₃(WO₄)₈ phosphor. The analysis of optical transition and Huang-Rhys factor reveals a weak electron-phonon coupling interaction. The temperature-dependent emission spectra also indicate that the as-prepared Li₃Ba₂Y₃(WO₄)₈:Eu³⁺ phosphor has better thermal stability than that of the commercial Y₂O₂S:Eu³⁺ phosphor. Therefore, our results show that the as-prepared Li₃Ba₂Y₃(WO₄)₈:Eu³⁺ phosphor is a promising candidate as red emitting component for white light emitting diodes (LEDs).     

Structural and spectroscopic analysis of green glowing down-converted BYO:Er3+ nanophosphors for pc-WLEDs

An energy efficient solution combustion technique was selected for fabricating a series of energy-efficient novel down-converted Ba₃Y₄O₉:Er³⁺ nanoparticles with green emission. Crystal structure engineering along with the morphological aspects was investigated via certain advanced characterizations such as Rietveld refinement and powder X-ray diffractometry (PXRD) procedure, microscopic practices like scanning and transmission electron microscope techniques, photoluminescence and diffuse reflectance spectroscopic analysis. Average crystallite size (65.71 nm–74.15 nm) and micro strain (0.0012) of the optimum powder nanomaterial were analyzed from high quality XRD data using Williamson-Hall (W–H) plot method. Alluring spectroscopic features were realized by photoluminescent (PL) spectra recorded upon excitation via near ultraviolet (NUV) source of 381 nm; displaying an intense emission peak (562 nm) situated in the visible region that is solely responsible for the green glow of the prepared phosphor. PL analysis witnessed a bright green emission via a reliable emanation transition (⁴S_3/2 → ⁴I_15/2) of Er³⁺ ions. Excellent colorimetric parameters of optimized nanophosphor like CIE coordinates (0.3420, 0.6064), 5356K CCT and 79.02% color purity validated its advanced photonic and optoelectronic applications for cool light emitting WLEDs, lasers, optical sensors, solar and photovoltaic cells.     

Photoluminescence enhancement of novel K(Y,Lu)CaWO6: Eu3+ red phosphor prepared by controllable citrate-EDTA complexing method

Novel double-perovskite K(Y_0.95-xLu_xEu_0.05)CaWO₆ red phosphors were successfully prepared by the controllable citrate-EDTA complexing method. XRD with structure refinement, FTIR, Raman and photoluminescence spectra were combined to systematically investigate the structure parameters and luminescence properties of prepared phosphors. The substitution of Lu³⁺ with smaller ionic radius resulted in the lower symmetry even with the same space group of C2/m, which was also directly observed from the red shift and splitting of Raman T_2?g(1) mode. The concentration higher than x?=?0.6 made the intensity alteration in the excitation spectra from charge transfer band to 4f?4f of Eu³⁺. The obvious enhancements of red emission at 615?nm were obtained under both blue and ultraviolet lights, respectively, and reached almost the same intensity at x?=?0.6. Meanwhile, the more standard red light could be found by the gradual shifts of CIE chromaticity coordinates and bigger ratio of red/orange emission. The substitution of Lu³⁺ improved the quality and emission intensity of red light of this double perovskite system and the composition optimized phosphor of K(Y_0.35Lu_0.6Eu_0.05)CaWO₆ exhibited great potential in the application of white LEDs.     

Synthesis and luminescence properties of novel Y2Si4N6C:Sm3+ carbonitride phosphor

Novel Y₂Si₄N₆C:Sm³⁺ phosphors for white light-emitting diodes (w-LEDs) were prepared by a carbothermal reduction and nitridation method. X-ray diffraction (XRD) and photoluminescence spectra were utilized to characterize the structure and luminescence properties of the as-synthesized phosphors. The emission spectrum obtained by excitation into 291 nm contains exclusively the characteristic emission of Sm³⁺ at 568, 607 and 654 nm which correspond to the transitions from ⁴G_5/2 to ⁶H_5/2, ⁶H_7/2, and ⁶H_9/2 of Sm³⁺, respectively. The strongest one is located at 607 nm due to ⁴G_5/2–⁶H_7/2 transition of Sm³⁺. It was found that concentration quenching occurred as a result of dipole–dipole interaction according to Dexter's theory. The temperature dependence of photoluminescence properties was investigated from 25 to 300 °C and the prepared Y₂Si₄N₆C:Sm³⁺ phosphors showed superior thermal quenching properties.     

Effects of argon sintering atmosphere on luminescence characteristics of Ca6BaP4O17:Sm3+ phosphors

In this paper, Ca₆BaP₄O₁₇:Sm³⁺ and Li⁺ co-doped Ca₆BaP₄O₁₇:Sm³⁺ phosphors were synthesized in air and argon atmospheres using a solid-state reaction method. The phosphor morphologies and crystal structure were studied using scanning electron microscopy and X-ray diffraction, respectively. The emission and absorption characteristics were investigated using photoluminescence emission spectroscopy and diffuse reflectance spectroscopy. The surface states and composition of phosphor were investigated using X-ray photoelectron spectroscopy. The emission integrated intensities of the phosphors sintered in an argon atmosphere increased 3.5 fold than the ones sintered in air atmosphere, with Li⁺ ions becoming embedded in the lattice of the Ca₆BaP₄O₁₇:Sm³⁺ phosphor. This occurs because there are fewer defect/oxygen vacancies and less of the secondary phase forms, leading to better Sm³⁺ emission. The results suggest that sintering a mixture of the raw materials of a phosphor in an argon atmosphere is a good approach for synthesizing Ca₆BaP₄O₁₇:Sm³⁺ phosphor powders. The color purity and CIE values of an optimized phosphor sample sintered in an argon atmosphere with an Li⁺ ion compensator were calculated to be ~ 99.6% and (0.612,0.386) in the orange–red region under 405-nm excitation, respectively. Moreover, the solid solubility of Sm³⁺ ions in the Ca₆BaP₄O₁₇ host can be enhanced by using an argon atmosphere in the synthesis process.     

Effect of Y3+-O2- partial substitution with Ca2+-F- on the luminescence enhancement of Y2Mo3O12:Sm3+ red-emitting phosphors

To improve the luminescence property of Sm³⁺ in Y₂Mo₃O₁₂, partial Ca²⁺-F^- co-substituted Y₂Mo₃O₁₂:Sm³⁺ phosphor, namely Y_2-xCa_xMo₃O_12-xF_x:Sm³⁺, was prepared using a solid-state method. The effect of introducing Ca²⁺-F^- ion pairs on structure and luminescence properties of Y₂Mo₃O₁₂:Sm³⁺ was studied in depth. XRD patterns not only manifested that all as-prepared Y_2-xCa_xMo₃O_12-xF_x:Sm³⁺ samples had standard Y₂Mo₃O₁₂ structure, but also indicated the introduction of Ca²⁺-F^- ion pairs did not cause the change of crystal structure. Under the near ultraviolet excitation of 404 nm, the emission peaks of Y₂Mo₃O₁₂:Sm³⁺ were located at 567 nm, 605 nm and 652 nm, respectively, resulting from the 4f→4f electron transitions of Sm³⁺ ions. Furthermore, the luminescence intensity of Sm³⁺ was obviously enhanced through the co-substitution of Y³⁺-O^2- ions with Ca²⁺-F^- ions in Y₂Mo₃O₁₂ structure, and the chromaticity coordinates moved towards red region, which due to the environmental effect of crystal field around Sm³⁺. Besides, the red LED device was manufactured for suitable chromaticity parameters. All results indicated that the as-prepared Y_1.84Ca_0.06Mo₃O_11.94F_0.06:0.10Sm³⁺ red-emitting phosphor could become a promising candidate for application of white light-emitting diodes and plant illumination.     

Novel orange-emitting Ba2LaNbO6:Eu3+ nanophosphors for NUV-based WLEDs and photocatalytic water purification

Energy conservation and environmental safety are the key requirements in the modern world. We report novel orange-emitting double perovskite Ba₂LaNbO₆:Eu³⁺ (BLN:Eu³⁺) nanophosphor fabricated using a citrate sol-gel method for use in general illumination and photocatalysis. After annealing at 800?℃, the particles exhibited a nanorod-like morphology with monoclinic structure. The photoluminescence emission spectra exhibited an intense ⁵D₀→⁷F₁ transition at 594?nm and a moderate ⁵D₀→⁷F₂ transition at 615?nm, demonstrating that the Eu³⁺ ions occupied the La³⁺ sites with inversion symmetry. The optimal concentration of Eu³⁺ ions was found to be about 5?mol% for the BLN host lattice. Energy transfer from the NbO₆^7- octahedrons to the Eu³⁺ ions was clearly witnessed when the BLN:Eu³⁺ nanophosphors were excited with both the characteristic excitation bands of Eu³⁺ (⁷F₀→⁵L₆) and NbO₆^7- octahedrons at 392 and 380?nm, respectively. The thermal quenching temperature of 5?mol% Eu³⁺ ions doped BLN nanophosphors was found to be 183?℃, indicating that these nanophosphors are very stable at high temperatures. In addition, the dye removal efficiency of the proposed BLN nanophosphors was verified using Rhodamine B (RhB) dye as a model pollutant under UV irradiation. Compared to a commercial nano-ZnO catalyst, our synthesized BLN nanophosphors showed superior RhB de-colorization efficiency. Therefore, the proposed BLN:Eu³⁺ nanophosphors are promising multifunctional materials for photocatalysis and general lighting applications.     

Garnet-based red emitting phosphors Li6MLa2Nb2O12: Eu (M=Ca,Sr, Ba): Photoluminescence improvement by changing crystal lattice

A series of novel red emitting phosphors Li₆M(La_1−xEu_x)₂Nb₂O₁₂ (M=Ca, Sr, Ba; 0≤x≤0.3) were synthesized by solid state reaction, and their structures and photoluminescence properties were investigated in detail. The excitation spectrum of Li₆M(La_1−xEu_x)₂Nb₂O₁₂ revealed two mainly excitation bands at 393 nm and 464 nm, which match well with the two popular emissions from near-UV and blue LED chips. Upon the 464 nm light excitation, Li₆MLa₂Nb₂O₁₂:Eu³⁺ phosphors exhibit a red emission centered at 608 nm, originated from the ⁵D₀–⁷F₂ transition of Eu³⁺ ions. The Eu³⁺ surrounding crystal lattice environment in the garnet-based host was changed by altering the c sites element with different radii alkaline earth Ba, Sr, and Ca. The evident photoluminescence enhancement was observed in Li₆M(La_1−xEu_x)₂Nb₂O₁₂ phosphors with the decreasing of the c sites ionic radius. The emission intensity of the optimized Li₆Ca(La_0.8Eu_0.2)₂Nb₂O₁₂ (λ_exc=464 nm) phosphor is about two times higher than that of Y₂O₃:Eu³⁺ (λ_exc=467 nm) under blue light excitation. In addition, the quenching mechanism and the relationship between the structure and photoluminescence property were also discussed.     

Electrical and photoluminescence properties of Sm3+ doped Na0.5La0.5Bi8-xSmxTi7O27 ceramics

In this study, Sm³⁺ doped Na_0.5La_0.5Bi_8-xSm_xTi₇O₂₇ (NBT-BITL-xSm, x = 0, 0.01, 0.015, 0.02, and 0.03) ceramics were synthesized via a conventional solid-state reaction process. The structural, electrical, and photoluminescence properties of NBT-BITL-xSm ceramics were systematically investigated. The crystal structure of NBT-BITL-xSm was refined using XRD Rietveld refinement and found to possess a single orthorhombic structure at room temperature. Raman spectroscopy revealed that Sm³⁺ ions preferred to substitute for Bi³⁺ located in the A-sites of pseudo-perovskite layers, inducing a slight decrease in orthorhombic distortion. Strong characteristic emission peaks of Sm³⁺ ions were observed in orange-red regions under a 407 nm laser source, and the sample with x = 0.015 achieved the optimal photoluminescent property. Dielectric measurements showed double anomaly permittivity peaks at the temperature of 589 and 600^°C (T_m and T_c, respectively). The complex impedance spectrum indicated that the electrical conductivities mainly originated from crystal grains at high temperature. The activation energy was calculated to be 1.37–1.44 eV from Arrhenius fitting results. After Sm³⁺ substitution, the activation energy for conductivity was increased as a result of reduced oxygen vacancies.