Cathodoluminescence and thermoluminescence of ZnB2O4:Eu3+ phosphors prepared via wet-chemical synthesis

In present work, a series of Eu doped zinc borate, ZnB₂O₄, phosphors prepared via wet chemical synthesis and their structural, surface morphology, cathodoluminescence (CL) and thermoluminescence (TL) properties have been studied. Phase purity and crystal structure of as-prepared samples are confirmed by X-ray diffraction measurements (XRD) and they were well consistent with PDF card No. 39-1126, indicating the formation of pure phase. The thermoluminescence (TL) behaviors of Eu activated ZnB₂O₄ host lattice are studied for various beta doses ranging from 0.1 to 10?Gy. The high-temperature peak of Eu activated sample located at 192?°C exhibited a linear dose response in the range of 0.1–10?Gy. Initial rise (IR) and peak shape (PS) methods were used to determine the activation energies of the trapping centres. The effects of the variable heating rate on TL behaviour of Eu activated ZnB₂O₄ were also studied. When excited using an electron beam induced light emission (i.e cathodoluminescence, CL) at room temperature (RT), the as-prepared phosphors generate reddish-orange color due to predominant emission peaks of Eu³⁺ ions located at 576–710?nm assigned to the ⁵D₀→⁷F_J (J=1,2,3, and 4) transitions. The maximum CL intensity for Eu³⁺ ions at 614?nm with transition ⁵D₀→⁷F₂ was reached Eu³⁺ concentration of 5?mol%; quenching occurred at higher concentrations. Strong emission peak for Eu³⁺ ions at 614?nm with transition ⁵D₀→⁷F₂ is observed. The CL experimental data indicate that ZnB₂O₄:Eu³⁺ phosphor as an orange-red emitting phosphor may be promising luminescence materials for the optoelectronic applications.     

Versatile fluorescent Gd2MoO6:Eu3+ nanophosphor for latent fingerprints and anti-counterfeiting applications

At present, latent fingerprint and anti-counterfeit detection technologies have become key factors in forensic science. Here, we report on the synthesis and characterizations of Eu³⁺ ions doped monoclinic Gd₂MoO₆ nanophosphors for latent fingerprints and anti-counterfeiting applications. The crystalline structure, phase purity and lattice parameters of Gd₂MoO₆:Eu³⁺ nanophosphors were investigated in detail using the X-ray diffraction and Rietveld refinement analyses. The photoluminescence excitation spectra of Gd₂MoO₆:Eu³⁺ nanophosphor unveiled their strong charge transfer band and characteristic f-f transitions of Eu³⁺ ions in the UV and near-UV regions. Whereas, the corresponding emission spectra showed an intense red emitting hypersensitive transition (⁵D₀→⁷F₂) with excellent CIE coordinates (0.6503, 0.3490). The concentration quenching of Eu³⁺ ions in Gd₂MoO₆ host lattice was observed at 5?mol%. The optimized Gd₂MoO₆:Eu³⁺ nanophosphor was used to detect the latent fingerprints and anti-counterfeits. The developed latent fingerprints fluorescent images enabled three levels of identifications with high contrast, selectivity and sensitivity. Also anti-counterfeit marker was successfully developed through handwriting and spray method. The obtained results of the synthesized Gd₂MoO₆:Eu³⁺ nanophosphors signifying their potential use in latent fingerprint and anti-counterfeit applications.     

White light emission from Eu co-activated Ca2Gd8Si6O26:Dy nanophosphors by solvothermalsynthesis

Ca₂Gd₈(SiO₄)₆O₂ (CGS) nanophosphors with different concentrations of single-doped Dy³⁺ ions and co-doped Dy³⁺/Eu³⁺ ions were prepared by a solvothermal synthesis. Very fine particles in the nanometer range could be achieved by this method, as evidenced by transmission electron microscope measurements. The hexagonal phase of the oxyapatite structure was confirmed by X-ray diffraction patterns. The energy transfer between Eu³⁺ and Dy³⁺ ions was investigated by photoluminescence excitation and emission properties. These phosphors had absorption bands in the UV and NUV region, which are suitable for the emission wavelength of UV or NUV light-emitting diodes (LEDs). With increasing the Eu³⁺ ion concentration, the emission peak intensity corresponding to the ⁵D₀→⁷F₂ transition increased and the yellow (⁴F_9/2→⁶H_13/2) emission intensity also increased compared to the blue (⁴F_9/2→⁶H_15/2) emission intensity due to the increased energy transfer between Dy³⁺ to Eu³⁺ ions. Thus, the Eu³⁺ ions compensated the red emission component of the Dy³⁺ doped CGS nanophosphors. Such phosphors are expected to have potential applications for NUV based white LEDs.     

Excitation-dependent energy transfer and color tunability in Dy3+/Eu3+ co-doped multi-component borophosphate glasses

Using the melt-quench technique, potassium zinc borophosphate (KZnBP) glasses incorporated with Dy³⁺, Eu³⁺, and Dy³⁺/Eu³⁺ ions individually and combinedly were prepared, and their photoluminescence (PL)-related features were investigated. The KZnBP glass containing an optimized content of Dy³⁺ (0.5 mol%) is co-doped with Eu³⁺ in various contents, and the energy transfer (ET) process between them was studied at λ_exci = 349, 364, 387 (Dy³⁺), and 394 nm (Eu³⁺). The Dy³⁺/Eu³⁺ co-doped system, when excited with Dy³⁺ excitations has resulted in a significant decrease in the intensity of Dy³⁺ peaks observed at 480 nm (⁴F_9/2→⁶H_15/2, blue) and 574 nm (⁴F_9/2→⁶H_13/2, yellow), with simultaneous enhancement of the intensity of Eu³⁺ peaks at 591 nm (⁵D₀→⁷F₁, orange) and 617 nm (⁵D₀→⁷F₂, red). This trend is due to the efficient energy transfer from Dy³⁺ to Eu³⁺, indicating that Eu³⁺ ions were sensitized by Dy³⁺ ions. Dexter's theory and the Inokuti–Hirayama (I–H) model revealed that the dipole–dipole interaction is accountable for the energy transfer from Dy³⁺ to Eu³⁺ through energy-transfer channels [⁴F_9/2(Dy³⁺)+⁷F_1,2(Eu³⁺)→⁶H_15/2(Dy³⁺)+⁵D₂(Eu³⁺)] and [⁴F_9/2(Dy³⁺)+⁷F₀(Eu³⁺)→⁶H_13/2(Dy³⁺)+⁵D₀(Eu³⁺)]. The color coordinates of the Dy³⁺/Eu³⁺ co-doped glasses under various excitations fall within the white light emission spectrum, indicating their potential application in warm white LEDs.     

Synthesis,structural characterization,and photoluminescence properties of TTB‐type PbTa2O6:Eu3+ phosphor

Undoped and Eu³⁺‐doped tetragonal tungsten bronze (TTB) PbTa₂O₆ phosphors were synthesized by using solid‐state reaction method. Synthesized samples were characterized by XRD, SEM‐EDS, and photoluminescence analyses. XRD results revealed TTB‐type crystal structure with single phase up to 10 mol% Eu³⁺ doping concentration. In SEM‐EDS analyses, elemental composition of Pb decreased with the increasing concentration of Eu³⁺. Emissions at the excitation wavelength of 398.5 nm were observed at 593.2 and 618.8 nm due to ⁵D₀→⁷F₁ transitions and ⁵D₀→⁷F₂ transitions, respectively. Emission increased with the increasing Eu³⁺ doping concentration up to 10 mol% and not observed concentration quenching.     

Spectroscopic investigations on high efficiency deep red-emitting Ca2SiO4:Eu3+ phosphors synthesized from agricultural waste

Europium doped calcium orthosilicate (Ca₂SiO₄) phosphors have been synthesized by the conventional high temperature solid-state reaction method in various concentrations from agricultural waste (egg shell as a CaO and rice husk as a SiO₂). These phosphors structure from X-ray diffraction and morphology from scanning electron microscopy have been examined. Concentration dependent Eu³⁺ ions luminescent properties in Ca₂SiO₄ phosphors have been studied from the excitation, emission and decay curves analysis. The ⁵D₀ → ⁷F_J transitions observed in luminescence spectrum allows to determine the site symmetry of the Eu³⁺ ion. A charge transfer band (CTB) at around 260?nm which is due to the Eu–O interaction in the host along with the 4f – 4f excitation bands due to Eu³⁺ ions in UV and blue regions are observed. The color co-ordinates determined from emission spectra varies with concentrations of Eu³⁺ ions and are found to fall in the red region. The decay curves show single exponential behavior for all concentrations of Eu³⁺ ions (0.01–0.4?mol%) and the lifetimes varied from 2.67 to 2.78?ms. It is worth noting that the present material is found to be far better than many red phosphors synthesized by using agricultural waste as raw materials.     

Synthesis and characterization of Eu3+-doped C12H18Ca3O18 phosphor

A series of Eu³⁺-doped C₁₂H₁₈Ca₃O₁₈ phosphors were synthesized through a facile hydrothermal method and the properties of as-prepared phosphors were explored by X-ray diffractometer (XRD), scanning electron microscope (SEM), and photoluminescence (PL) spectrometer. The exploration results indicated that the C₁₂H₁₈Ca₃O_18:Eu³⁺ had been successfully synthesized. The morphology of C₁₂H₁₈Ca₃O_18:Eu³⁺ was a strip with the size of 100–4000 nm × 50–400 nm × 50–200 nm and the ratio of length to width of 2–80. The strongest emission peak of C₁₂H₁₈Ca₃O_18:Eu³⁺ around 620 nm was ascribed to ⁵D_o→⁷F₂ transition of Eu³⁺, and the peaks centered at 590, 653 and 694 nm respectively corresponded to ⁵D_o →⁷F₁, ⁷F₃, and ⁷F₄ transitions. C₁₂H₁₈Ca₃O_18: Eu³⁺ gave the red light emission, as indicated by color coordinate analysis. The photoluminescence intensity of the phosphors prepared under the Eu³⁺ concentration of 6% was the highest. The crystal structure of C₁₂H₁₈Ca₃O_18:Eu³⁺ was changed after europium ions occupied the lattice position of calcium ions. Europium ion could displace calcium arbitrarily. As a new kind of matrix, calcium citrate possesses the properties of both organic and inorganic compounds and the luminescent C₁₂H₁₈Ca₃O₁₈: x Eu³⁺ particles may be applied in biological fluorescent tags and luminescent materials.     

Study of Eu3+–Gd3+ co-doped Ba–Bi–B glasses for red-laser applications: Physical,structural, photoluminescence and time-resolved spectral characteristics

A series of Eu³⁺ and Eu³⁺/Gd³⁺ co-doped barium-bismuth-borate (Ba–Bi–B) glasses were prepared by melt-quench technique. And deliberated the physical, structural, and spectroscopic properties of all glasses and explored the energy transfer process from Gd³⁺ to Eu³⁺ ions. The density of glasses increased with increasing of Gd³⁺ concentration in co-doped glasses. Characteristics of steady-state and time-resolved photoluminescence (PL) of Eu-doped and Eu³⁺-Gd³⁺ co-doped glasses under different excitation wavelengths suggested the prospects of the investigated glass system for display device applications. PL spectrum displays a strong red emission peak centered at 612 nm due to the Eu³⁺: ⁵D₀→ ⁷F₂ transition. Less intense emissions centered at 577 nm (⁷F₀), 590 nm (⁷F₁), 651 nm (⁷F₃) and 700 nm (⁷F₄) are also observed from the radiative transitions of the excited state ⁵D₀ of Eu³⁺ions. The values of radiative parameters such as transition probability, branching ratios, and stimulated emission cross-sections were obtained from Judd–Ofelt theory analysis and indicated the aptness of the Ba–Bi–B glasses for optical devices. A 5-fold enhancement in the PL intensity was observed in 1.0 mol% Eu³⁺ and 3.0 mol% Gd³⁺ co-doped glass under λ_Exci. = 394 nm excitation. The calculated commission Internationale de l'eclairage color coordinates and correlated color temperature values show that the Ba–Bi–B glasses are useful for red-laser and display device applications.     

Photoluminescence properties of Eu3+-doped stalk-like Al2O3 via a hydrothermal route followed by heat treatment

ABSTRACT

Uniform Al₂O₃:Eu³⁺ samples were successfully fabricated via a hydrothermal method and subsequent thermal decomposition of Eu³⁺-doped precursors. The sample characterisations were carried out by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectra. XRD results revealed Eu³⁺-doped samples were a pure γ-Al₂O₃ phase after being calcined at 1173?K. SEM results showed that these Eu³⁺-doped Al₂O₃ samples were stalk-like, with an average length of 1.5?μm. Upon excitation at 394?nm, the orange–red emission bands, having wavelengths longer than 580?nm, were to be from ⁵D₀→⁷F_J (J?=?1, 2) transitions. The asymmetry ratio of (⁵D₀→⁷F₂)/(⁵D₀→⁷F₁) intensity is about 0.54, 2.76, 3.29, 2.86, 3.36, 3.13 for Eu³⁺ concentrations of 0.1, 0.4, 0.7, 1.0, 1.5 and 2.0?mol-%, respectively. The optimal doping concentration of Eu³⁺ ions in Al₂O₃ is 1.5?mol-%. According to Dexter's theory, the critical distance between Eu³⁺ ions for energy transfer was determined to be 14?Å.     

Preparation and luminescence properties of Eu2O3 doped glass-ceramics containing NaY(MoO4)2

Eu₂O₃ doped transparent glass-ceramics containing NaY(MoO₄)₂ crystalline phase were prepared via melting-crystallization. The optimum heat treatment condition (660℃/3h) was determined by DSC, XRD, SEM and transmittance curves. The transmittance of glass-ceramic can reach 80 % in the visible region. The emission spectra of Eu₂O₃ doped glass-ceramics consist of Eu³⁺ ions characteristic emission peaks at 591nm (⁵D₀→⁷F₁) and 614nm (⁵D₀→⁷F₂). The optimal doping concentration of Eu₂O₃ in the glass-ceramics is 0.9 mol%, and fluorescence lifetime is 1.37042ms. The change of the ratio of red emission intensity to orange emission intensity leads to the shift of chromaticity coordinates from orange to red region, and the chromaticity coordinate (0.6337, 0.3635) of 0.9 mol% Eu₂O₃ doped glass-ceramic is closest to the standard red light coordinate. The results show that this kind of glass-ceramic is expected to be good red emission material.     

Synthesis and characterization of cellulose ethers/Eu(III)

The coordination complexes of the crystalline structure of cellulose ethers/Eu(III) with fluorescence emission, viz CMC/Eu(III), MC/Eu(III), and HEC/Eu(III), were synthesized and characterized. Results showed the emission spectra of Eu³⁺ ions in these coordination compounds, which originates from electric dipole transition. The main emission peak at 615 nm generated from ⁵D₀→⁷F₂ transition of Eu³⁺ ions. Their absorption and excitation spectra were different, because the effect of the high polarity of water and having both hydrogen bond donor and acceptor properties on the excited molecule is different from the effect on the ground state of the molecule. Our study demonstrated that the Degree of Substitute (DS) of CMC could influence the fluorescence intensity (FI) of CMC/Eu(III). The emission intensity of CMC/Eu(III) varies with the DS of CMC. For example, when the DS of CMC was 0.89, the FS (fluorescent spectra) of solid CMC/Eu(III) displayed three emission peaks Eu(III): the strongest emission peak at 615 nm (⁵D₀→⁷F₂ transition) and other two weaker peaks at 583 nm (⁵D₀→⁷F₁ transition) and at 652 nm (⁵D₀→⁷F₃ transition), respectively. The concentration of Eu(III) could also affect the FI of these coordination complexes. The FI of the coordination complexes peaked at 615 nm all reached maximum when Eu³⁺ concentration was at 5% (wt/wt). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 743–747, 2005     

Microstructure of Eu3+‐Doped Perovskites‐Type Niobate Ceramic La3Mg2NbO9

Eu³⁺‐doped red‐emitting ceramics of Eu³⁺‐doped La₃Mg₂NbO₉ were prepared via typical solid state. X‐ray diffraction and scanning electron microscope were utilized to characterize the ceramics. The photoluminescence excitation and emission spectra, the fluorescence decay curves, and color coordinates were investigated. The concentration quenching of the samples were discussed as well. The microstructures of the ceramics were discussed according to the spectral properties of probe ions of Eu³⁺, for example, substitution sites for Eu³⁺, inhomogeneous broadening and splitting of the emission bands, nonexponential decay, ⁵D₀→⁷F₀ emission transition, distorted symmetry sites, etc. The crystal structure of La₃Mg₂NbO₉ is heavily distorted due to the mixed occupation of Mg and Nb on B sites. Eu³⁺ ions only substitute La³⁺ sites and Eu³⁺ ions (or rare‐earth ions) are arranged in the heavily disordered environments over the whole structure in La₃Mg₂NbO₉.     

Luminescent properties of MgAl2O4 ceramics doped with rare earth ions fabricated by spark plasma sintering technique

MgAl₂O₄ ceramics doped with rare earth ions (Eu²⁺ and Ce³⁺ ions) were fabricated by spark plasma sintering technique. A complex characterization of the crystalline and defect structure of the ceramic by XRD was carried out. Absorption, excitation, photo- and cathodoluminescence spectra were studied. The photoluminescence spectrum shifts to the blue region with a maximum at λ_em =?475?nm for the MAS:0.1Ce ceramics. The nature of this luminescence can be caused by the radiative transitions in the cerium ion 5d–4f. The emission spectrum of MAS:0.1Eu has a “green” band emission in range of 400–700?nm centered around 500?nm, which can be ascribed to the allowed 4f⁶5d¹→4f⁷ (5d–4f) transition of Eu²⁺. In the millisecond time range, simultaneously with the emission of the complex host centers, the impurity luminescence bands of the chromium ion are recorded. It was shown that cathodoluminescence spectra in nanosecond time range can be decomposed into several emission bands at 2.72, 3.01, 3.37, 3.63–3.82?eV caused by F-type centers. It was demonstrated that the Eu²⁺ and Ce³⁺ ions lead to change the intensity ratio of the luminescence bands. The luminescence decay kinetics of synthesized spinel ceramics in nano- and millisecond time range were investigated in detail.     

Preparation and photoluminescence enhancement of Au nanoparticles embedded LaPO4:Eu3+ inverse opals

In this work, we present a facile preparation approach of Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opal photonic crystals. In the typical preparation process, the transparent LaPO₄:Eu³⁺ sol including HAuCI₄ was infiltrated into the opal templates. After the sintering, the 10‐20 nm Au nanoparticles were formed in the interior of nano‐sized wall of LaPO₄:Eu³⁺ inverse opal and the Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opals were obtained. The luminescence of Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opal was investigated. The emission peaks located at the 593 (⁵D₀→⁷F₁), 618 (⁵D₀→⁷F₂) and 698 nm (⁵D₀→⁷F₄) from Eu³⁺ ions were observed. The 593, 618, and 698 nm emissions of Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opals were enhanced in contrast to these of LaPO₄:Eu³⁺ inverse opal without the Au nanoparticles, which is from the excitation field enhancement caused by the localized surface plasmon resonance of Au nanoparticles.     

Mn4+-activated KLaMgWO6: A new high-efficiency far-red phosphor for indoor plant growth LEDs

Novel Mn⁴⁺-activated KLaMgWO₆ red phosphors with different Mn⁴⁺ concentrations were successfully synthesized via a high-temperature solid-state reaction method. The phase formation, microstructure, photoluminescence properties, decay lifetimes and internal quantum efficiency were discussed to analyze the properties of the as-prepared phosphors. The samples belonged to monoclinic crystal system with enough WO₆ octahedrons that provided suitable sites for Mn⁴⁺ ions. Upon the excitation of 348?nm, KLaMgWO₆:Mn⁴⁺ phosphors gave bright far-red emission around 696?nm due to the ²E_g→⁴A_2g transition of Mn⁴⁺ ions. The critical concentration of Mn⁴⁺ was 0.6?mol% and the concentration quenching mechanism belonged to electric multipolar interaction. Besides, the CIE chromaticity coordinates of the KLaMgWO₆:0.6%Mn⁴⁺ phosphor were (0.7205, 0.2794) which located in deep red range, and its color purity reached up to 96.6%. The KLaMgWO₆:0.6%Mn⁴⁺ sample also exhibited high internal quantum efficiency of 43%. All of the admirable optical properties indicate that the KLaMgWO₆:Mn⁴⁺ phosphors can be applied to indoor plant growth illumination.     

Preparation and fluorescence properties of Zn2SnO4:Eu3+ orange emitting afterglow phosphor

In this study, an orange emitting afterglow phosphor of Zn₂SnO₄:Eu³⁺ was fabricated using the co-precipitation & hydrothermal method, and then annealed in Ar atmosphere at 1000 °C. X-ray diffraction, Raman spectra, EDX, fluorescence spectrometer, SEM and TEM were performed to characterize the target products. As revealed from the XRD analysis results, the fabricated product was the cubic inverse spinel structure Zn₂SnO₄ (JCPDS 24–1470) exhibiting high crystallinity. As confirmed by Raman and EDX spectra, the target product was Zn₂SnO₄:Eu³⁺. As Zn₂SnO₄:Eu³⁺ was excited at 347 nm, its fluorescence spectra showed the magnetic dipole emission at 589 nm and the electric dipole transition at 610 nm, complying with the transitions of Eu³⁺ ions from ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂. Meantime, Zn₂SnO₄:Eu³⁺ phosphors displayed an orange afterglow, and its attenuating characteristics met the exponential equation. Moreover, the optimal doping amount of Eu³⁺ ions was 15 mol%, and the concentration quenching took place by the cross relaxation. The color coordinate of the product (x = 0.15) was determined as (0.522, 0.4635), and the color purity reached 98.3%.     

A high quantum yield red phosphor NaGdSiO4: Eu3+ with intense emissions from the 5D0→7F1,2 transition

Red phosphors with a high quantum yield and a lower thermal quenching are needed to improve the luminescence efficiency and the stability of phosphor-converted white light-emitting diodes (pc-WLEDs). We have designed a high quantum yield NaGdSiO₄ (NGSO) based phosphor with enhanced Eu³⁺ emissions of the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions. This design is based on the Eu³⁺ at both the inversion and non-inversion symmetry sites. In detail, we have studied the structure, morphology, and luminescence properties of NGSO: Eu³⁺ phosphors. Using a 394 nm UV excitation, a series of Eu³⁺ emissions of ⁵D₀→⁷F_J (0–4) transitions has been observed. The internal quantum efficiency (IQE) is 83.42% and the red color purity is 91.4%. These values are much higher than some reported results. The higher IQE and double intense ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ emissions might originate from an unusual structure disorder around Eu³⁺ ions in the NGSO lattice. The lifetime of the optimal phosphor NGSO: 0.5Eu³⁺ is about 2 ms, suitable for solid-state lighting. The intensities of the strong emissions at 595 and 624 nm of NGSO: 0.5Eu³⁺ at 150 °C is about 85% of that at 30 °C, demonstrating its excellent thermal stability. Furthermore, this red NGSO: 0.5Eu³⁺ phosphor was packaged into a warm pc-WLED, exhibiting a lower correlated color temperature (CCT) of 4222 K and a comparable color rendering index (CRI) of 86.7. These results show that this red phosphor could act as a red component of pc-WLEDs excited by the n-UV LED chip.     

Synthesis and photoluminescence enhancement of Ca3Sr3(VO4)4:Eu3+ red phosphors by co-doping with La3+

In this study, a series of red-emitting Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphors co-doped with La³⁺ was prepared using the combustion method. The microstructures, morphologies, and photoluminescence properties of the phosphors were investigated. All Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ samples synthesized at temperatures greater than 700 ℃ exhibited the same standard rhombohedral structure of Ca₃Sr₃(VO₄)₄. Furthermore, the Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ phosphor was effectively excited by near-ultraviolet light of 393 nm and blue light of 464 nm. The strong excitation peak at 464 nm corresponded to the ⁷F₀→⁵D₂ electron transition of Eu³⁺. The strong emission peak observed at 619 nm corresponded to the ⁵D₀→⁷F₂ electron transition of Eu³⁺. Co-doping with La³⁺ significantly improved the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺ red phosphors. The optimum luminescence of the phosphor was observed at Eu³⁺ and La³⁺ concentrations of 5% and 6%, respectively. Moreover, co-doping with La³⁺ also improved the fluorescence lifetime and thermal stability of the Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphor. The CIE chromaticity coordinate of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ was closer to the NTSC standard for red phosphors than those of other commercial phosphors; moreover, it had greater color purity than that of all the samples tested. The red emission intensity of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ at 619 nm was ~1.53 times that of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺ and 2.63 times that of SrS:Eu²⁺. The introduction of charge compensators could further increase the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ red phosphors. The phosphors synthesized herein are promising red-emitting phosphors for applications in white light-emitting diodes under irradiation by blue chips.     

The luminescence and structural characteristics of Eu-doped NaBaPO4 phosphor

Eu³⁺-doped NaBaPO₄ was prepared by a high-temperature solid-state reaction. The phase formation was confirmed by X-ray powder diffraction measurements. The laser site-selective excitation and emission spectra have been investigated in the ⁵D₀ → ⁷F₀ region by using a pulsed, tunable and narrowband dye laser. The excitation spectra corresponding to the ⁷F₀ → ⁵D₀ transition consist of two transitions at 579.6 nm Eu(I) and 578.9 nm Eu(II), indicating the Eu³⁺ ions occupy two crystallographic sites of Ba²⁺ ions. The decay lifetimes of the two Eu³⁺ sites were measured. Two crystallographic sites for Eu³⁺ ions doped in NaBaPO₄ lattice were assigned from the luminescence characteristic and structure features. Meanwhile, the charge compensation mechanism of Eu³⁺ doping in NaBaPO₄ was discussed.     

Structural and spectral properties of red light emitting Eu3+ activated TiO2 nanophosphor for white LED application

The structural and luminescent properties of Eu³⁺ doped TiO₂ nanophosphors synthesized by low cost combustion method were investigated. The X-ray diffraction analysis revealed that crystallite size decreases with doping concentration. Lattice volume expansion occurred due to the substitution of Ti⁴⁺ ions by larger ionic radii ions Eu³⁺. FESEM images showed prepared phosphors to be nano size spherical shaped particles. Energy band gap of 3 mol% Eu³⁺ doped samples decreased to 3.15 eV due to doping effect. The Eu³⁺ doped TiO₂ nanophosphors exhibited main red emission peak centered at 616 nm under 395 nm UV light excitation. Concentration quenching was observed at 3 mol% doping, that has been ascribed to dipole-dipole interaction. The covalent nature of Eu-O bond and environment around Eu³⁺ ions were discussed using Judd-Ofelt (J-O) intensity parameters. Internal quantum efficiency was calculated using excited state lifetime ⁵D₀ state of Eu³⁺ ion and J-O theory. The CIE colour coordinates and colour purity were calculated using the spectral energy distribution function. Low excited state life time indicated that Eu³⁺ doped TiO₂ can be used as red emitting phosphor for white light emitting diode applications.