Synthesis,characterization, and photoluminescence of SrBPO5:R,Na+ (R = Eu3+, Tb3+) phosphor for solid state lighting

A series of phosphors SrBPO₅:R,Na⁺ (R = Eu³⁺, Tb³⁺) were prepared by high-temperature solid-state synthesis, and their phase purity, morphology, IR spectra, and UV-Vis photoluminescence properties were investigated. The f-f transitions of Eu³⁺ and Tb³⁺ ions in the host lattice were assigned and discussed. The excitation and emission spectra indicate that SrBPO₅:Eu³⁺,Na⁺ and SrBPO₅:Tb³⁺,Na⁺ can be effectively excited by ultraviolet (394 and 370 nm), and exhibit reddish orange emission and yellowish green emission, respectively. The influence of the doping concentration on the relative emission intensity of Eu³⁺/Tb³⁺ was investigated, and the critical distance R_c was estimated in term of the concentration quenching data. The present study suggests SrBPO₅:R,Na⁺ (R = Eu³⁺, Tb³⁺) phosphor can be a potential candidate as an UV-convertible phosphor for white light-emitting diodes (LEDs).     

Spectroscopic Investigation of the Europium(3+) Ion in a New ZnY4W3O16 Matrix

A new Zn and Eu tungstate was characterized by spectroscopic techniques. This tungstate, of the formula ZnEu₄W₃O₁₆, crystallized in the orthorhombic system and was synthesized by a solid‐state reaction. It melts incongruently at 1330°. The luminescent properties, including excitation and emission processes, luminescent dynamics, and local environments of the Eu³⁺ ions in ZnEu₄W₃O₁₆ and ZnY₄W₃O₁₆ : Eu³⁺ diluted phases (1, 5, and 10 mol‐% of Eu³⁺ ion) were studied basing on the f⁶‐intraconfigurational transitions in the 250–720 nm spectral range. The excitation spectra of this system (λ_em 615 and 470 nm) show broad bands with maxima at 265 and 315 nm related to the ligand‐to‐metal charge‐transfer (LMCT) states. The emission spectra under excitation at the O→W (265 nm) and O→Eu³⁺ (315 nm) LMCT states present the blue‐green emission bands. The emission of tungstate groups mainly originate from the charge‐transfer state of excited 2p orbitals of O^2? to the empty orbitals of the central W⁶⁺ ions. On the other hand, in the emission of the Eu³⁺ ions, both the charge transfer from O^2? to Eu³⁺ and the energy transfer from W⁶⁺ ions to Eu³⁺ are involved. The emission spectra under excitation at the ⁷F₀→⁵L₆ transition of the Eu³⁺ ion (394 nm) of ZnY₄W₃O₁₆ : Eu³⁺ diluted samples show narrow emission lines from the ⁵D₃, ⁵D₂, and ⁵D₁ emitting states. The effect of the active‐ion (Eu³⁺) concentration on the colorimetric characteristic of the emissions of the compound under investigation are presented.     

Luminescence and dielectric properties of nano-structured Eu3+:K2O–Nb2O5–SiO2 glass-ceramics

In the present study, results concerning luminescence and dielectric properties of Eu₂O₃ (0.5 wt% in excess) doped nano-crystallized KNbO₃ containing transparent glass-ceramics obtained from glass of composition 25K₂O–25Nb₂O₅–50SiO₂ (mol%) by varied heat-treatment duration at 800 °C have been analyzed and reported. The formed crystallization phase, crystallite size and morphology have been examined through XRD, FESEM, TEM and FTIRRS measurements. The observed steep increase in the dielectric constant (?) of glass-ceramics over the as-prepared glass is attributed to the formation of ferroelectric nano-crystalline KNbO₃ in glass matrix. The absorption spectra of all the samples have revealed the characteristic 4f–4f intraband absorption transitions of Eu³⁺ ions. The measured photoluminescence spectra have exhibited emission transitions ⁵D_{0, 1} → ⁷F_j (j = 0, 1, 2, 3 and 4) of Eu³⁺ ions. The excited level lifetimes have been determined from measured fluorescence decay curves. The rare earth ion site symmetry (nearly C_v) has been understood based on the nature of the Stark splittings of emission bands detected in both Eu³⁺: glass and Eu³⁺: glass-ceramics.     

VUV-UV Photoluminescence Spectra of Strontium Orthophosphate Doped with Rare Earth Ions

The measurements of VUV-UV photoluminescence emission (PL) and photoluminescence excitation (PLE) spectra of rare earth ions activated strontium orthophosphate [Sr₃(PO₄)₂:RE, RE = Ce, Sm, Eu, Tb] are performed. Whenever the samples are excited by VUV or UV light, the typical emission of Ce³⁺, Sm³⁺, Eu³⁺, Eu²⁺ and Tb³⁺ ions can be observed in PL spectra, respectively. The charge transfer bands (CTBs) of Sm³⁺ and Eu³⁺ are found, respectively, peaking at 206 and 230 nm. The absorption bands peaking in the region of 150-160 nm are assigned to the host lattice sensitization bands, i.e., the band-to-band transitions of PO₄³⁻ grouping in Sr₃(PO₄)₂. It is speculated that the first f-d transitions of Sm³⁺ (Eu³⁺), and the CTB of Tb³⁺are, respectively, located around 165 (1 4 3) and 167 nm by means of VUV-UV PLE spectra and relational empirical formula, these f-d transitions or CT bands are included in the bands with the maxima at 150-160 nm, respectively. The valence change of europium from trivalent to divalent in strontium orthophosphate prepared in air is observed by VUV-UV PL and PLE spectra.     

Eu2+ & Mn2+‐Coactivated Ba3Gd(PO4)3 Orange‐Yellow‐Emitting Phosphor with Tunable Color Tone for UV‐Excited White LEDs

A novel orange‐yellow‐emitting Ba₃Gd(PO₄)₃:x Eu²⁺,y Mn²⁺ phosphor is prepared by high‐temperature solid‐state reaction. The crystal structure of Ba₃Gd(PO₄)₃:0.005 Eu²⁺,0.04 Mn²⁺ is determined by Rietveld refinement analysis on powder X‐ray diffraction data, which shows that the cations are disordered on a single crystallographic site and the oxygen atoms are distributed over two partially occupied sites. The photoluminescence excitation spectra show that the developed phosphor has an efficient broad absorption band ranging from 230 to 420 nm, perfectly matching the characteristic emission of UV‐light emitting diode (LED) chips. The emission spectra show that the obtained phosphors possess tunable color emissions from yellowish‐green through yellow and ultimately to reddish‐orange by simply adjusting the Mn²⁺ content (y) in Ba₃Gd(PO₄)₃:0.005 Eu²⁺,y Mn²⁺ host. The tunable color emissions origin from the change in intensity between the 4f–5d transitions in the Eu²⁺ ions and the ⁴T₁‐⁶A₁ transitions of the Mn²⁺ ions through the energy transfer from the Eu²⁺ to the Mn²⁺ ions. In addition, the mechanism of the energy transfer between the Eu²⁺ and Mn²⁺ ions are also studied in terms of the Inokuti–Hirayama theoretical model. The present results indicate that this novel orange‐yellow‐emitting phosphor can be used as a potential candidate for the application in white LEDs.     

Excitation-dependent variation in local symmetry in Ba2Mg(BO3)2 evidenced by Eu3+ luminescent structural probe

Eu³⁺ luminescence was studied in Ba₂Mg(BO₃)₂ by selectively substituting at Mg site. The parent host Ba₂Mg(BO₃)₂ and Ba₂Mg_0.9Eu_0.05Li_0.05(BO₃)₂ were synthesized by conventional solid state reaction method. Their isostructural nature was confirmed using powder X-ray diffraction technique. The photoluminescence excitation spectrum of Eu³⁺ exhibited a broad Eu³⁺O²⁻ charge transfer band with a maximum at 253 nm along with other excitation transitions. The emission characteristics of Eu³⁺ were found to be excitation wavelength-dependent. The equally intense magnetic and electric dipole transitions for excitation under longer wavelengths showed the presence of Eu³⁺ at a site with non-inversion symmetry. Excitation using 253 nm resulted in the predominant magnetic dipole transition revealing Eu³⁺ at a site with inversion symmetry. The difference in the relative intensities of magnetic and electric dipole transitions originates from the change in symmetry around Eu³⁺ in Ba₂Mg(BO₃)₂ under different excitations.     

Synthesis,Characterization and Luminescent Properties of La2Zr2O7:Eu3+ Nanorods

The Eu³⁺-doped La₂Zr₂O₇ phosphor with rod-like morphology was successfully synthesized by conventional solid state reaction and hydrothermal method. X-ray diffraction patterns, transmission electron microscopy, and photoluminescence spectra were employed to charac-terize its structure and morphology as well as luminescent properties. The results indicated that the red-emitting phosphor La₂Zr₂O₇:Eu³⁺ had well crystallized and belonged to the cubic structure with space group of Fd3m. The as-obtained product mainly appeared as straight nanorods with an average diameter of 47 nm and length of 50-700 nm. The pos-sible growth mechanism was also discussed. It was found that under blue excitation with a wavelength of 466 nm, the La₂Zr₂O₇:Eu³⁺ phosphor exhibited a characteristic red emission at 616 nm that was attributed to the hypersensitive ⁵DO_→⁷F2 _{electric dipole transition of Eu³⁺ ions. Meanwhile, it was more interesting to note that the emission of ⁵D}1_→⁷FJ _{(J=0, 1, 2) transitions and the splitting patterns of ⁵D}0_→⁷FJ _{(J=1, 2, 4) transitions of Eu³⁺ ions can be observed in the luminescent spectra of La2Zr2O7:Eu³⁺. It was demonstrated that Eu³⁺ preferred to occupy a low symmetry site.}     

Silica-Coated CaF2:Eu3+ Nanoparticles Functionalized with Oxalic Acid for Bio-conjugation to BSA Proteins

A new method for silica‐coated CaF₂:Eu³⁺ core‐shell nanoparticles functionalized with oxalic acid for bio‐conjugation to bovine serum albumin (BSA) proteins has been developed. Moreover, CaF₂:Eu³⁺/SiO₂ core‐shell nanoparticles modified with oxalic acid are biocompatible and can be dispersed in water. As an organic functional molecule, oxalic acid is able to react with hydroxyl groups existed on the surface of SiO₂ layer by esterification reaction to form carboxylic acid for further bio‐conjugation with BSA. The final products were characterized by means of X‐ray diffraction (XRD), transmission electron microscope (TEM), field‐emission scanning electron microscopy (FE‐SEM), ultraviolet (UV) spectrophotometer, infrared (IR) spectrophotometer and photoluminescence (PL) spectra. XRD result confirmed the phase purity of CaF₂:10 mol% Eu³⁺ and CaF₂:10 mol% Eu³⁺/SiO₂ nanoparticles obtained from the quaternary reverse micelles of cetyltrimethylammonium bromide (CTAB), cyclohexane, n‐pentanol and water. Images of TEM and FE‐SEM showed that the average grain sizes of CaF₂:10 mol% Eu³⁺/SiO₂ and bio‐conjugation of CaF₂:10 mol% Eu³⁺/SiO₂ nanoparticles with BSA were about 17 nm. The patterns of UV and IR spectra showed that BSA was linked to CaF₂:10 mol% Eu³⁺/SiO₂ nanoparticles. In the emission spectrum of CaF₂:10 mol% Eu³⁺/SiO₂ conjugated by BSA nanoparticles, characteristic emission peaks of Eu³⁺ within the wavelength ranging from 500 to 700 nm were observed, which is corresponding to the transitions from the excited ⁵D₀ levels to ⁷F_J levels. This confirmed that the Eu³⁺ dopant ion is located in a Ca²⁺ crystal site with T_d symmetry. CaF₂:10 mol% Eu³⁺/SiO₂ conjugated by BSA nanoparticles remain stable in aqueous media within 15 d with pH ranging from 2 to 9. Therefore, these luminescent colloidal nanoparticles can be potentially employed as targeted fluorescent labels in biomedical research applications.     

Structure and spectroscopic properties of (Y,Eu)(PO3)3 polyphosphate red phosphors

A series of orange-red emitting phosphor Y(PO₃)₃: xEu³⁺ (x = 0.1–1.0) was prepared by a solid-state reaction route. The phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) as well as decay lifetimes. Studies revealed the phase transfer from monoclinic to orthorhombic when Y³⁺ is totally replaced by Eu³⁺, and expansion of the unit cell occurs with increasing Eu³⁺ doped content. The PL spectra show that the phosphors Y(PO₃)₃: xEu³⁺ can be effectively excited by near ultraviolet (n-UV) light, and exhibit strong red-orange emission with no concentration quenching. The profile of PL spectra changes significantly at high Eu³⁺ content (x ≥ 0.80), which is due to the variation of preference for substitution of Eu³⁺. The luminescence due to the ⁵D₀ → ⁷F_J (J = 1, 2) transitions at 77 K exhibits its own spectral features for different crystallographic site. It is found that Eu³⁺ ions occupy the centers of octahedral polyhedron and form C_i/C₁ point group in Y(PO₃)₃.     

Determination of the optimum Eu3+-concentration in LaAlO3:Euphosphors by X-ray diffraction and fluorescence measurements

Combining X-ray powder diffraction with fluorescence measurements is an efficient way to determine the optimum activator concentration of inorganic phosphors. La_1?xEu_xAlO₃ samples (perowskite structure), prepared by solid state reactions with 0.5<x<5.0 at 1480 K, were investigated by both analytical methods. The luminescence emission spectra show strong ⁵D₀-⁷F₁ and ⁵D₀-⁷D₂ transitions and fluorescence intensity reaches a maximum at 1 mol% Eu³⁺. X-ray diffraction shows the formation of an EuAlO₃ phase at Eu³⁺ concentration above 1 mol%. Below 1 mol%, Eu³⁺ substitutes for La³⁺, as can be seen from the change in the lattice constant c.     

Structural, optical and thermal studies of Eu ions in lithium fluoroborate glasses

Borate glasses doped with trivalent europium were prepared by the conventional melt quenching technique, in the chemical composition of (49.99-x)B₂O₃ + 25Li₂O + 25LiF+xEu₂O₃ by varying the concentration of the rare earth ion in the order 0.01, 0.1, 1, 2 and 3 wt% and their structural, luminescence and thermal behavior have been reported. The XRD and FTIR spectra reveal the glass structure and the functional groups. The UV–VIS, luminescence spectra and lifetime of the Eu³⁺ ions were measured. The local site symmetry around the Eu³⁺ ions were evaluated through the luminescence intensity ratio (R) of the ⁵D₀ → ⁷F₂ to ⁵D₀ → ⁷F₁ transitions. Optical measurements have been carried out to explore the optical properties such as bonding parameters, Judd–Ofelt parameters, stimulated emission cross-section, transition probability, branching ratio, radiative lifetime, etc. The lifetime measurements of the ⁵D₀ level as a function of the concentration of Eu³⁺ ion have been found and is comparable to other reported for Eu³⁺ doped borate, phosphate glasses and higher than that for the tellurite glasses. The thermal properties such as glass transition, crystallization and melting temperatures of the Eu³⁺ glasses were studied through the DSC traces in the temperature range of 30−1200 °C at a heating rate of 10 °C per minute. The change in optical properties with the variation of Eu³⁺ ion concentration have been discussed and compared with similar results.     

Determination of the optimum Eu3+-concentration in LaAlO3:Euphosphors by X-ray diffraction and fluorescence measurements

Combining X-ray powder diffraction with fluorescence measurements is an efficient way to determine the optimum activator concentration of inorganic phosphors. La_1–xEu_xAlO₃ samples (perowskite structure), prepared by solid state reactions with 0.55D₀-⁷F₁ and ⁵D₀-⁷D₂ transitions and fluorescence intensity reaches a maximum at 1 mol% Eu³⁺. X-ray diffraction shows the formation of an EuAlO₃ phase at Eu³⁺ concentration above 1 mol%. Below 1 mol%, Eu³⁺ substitutes for La³⁺, as can be seen from the change in the lattice constant c.     

Effect of SnO2 Nanocrystals on the Emission of Eu3+ Ions in Silica Matrix

Silica xerogels containing Eu³⁺ ions and SnO₂ nanocrystals were prepared in the sol‐gel process, and characterized by x‐ray diffraction (XRD) and photoluminescence spectra. Under the excitation at 393 nm, characteristic emission of Eu³⁺ ions at 614 nm was enhanced with increasing amount of SnO₂ nanocrystals. Moreover, when the Eu³⁺/SnO₂ co‐doped samples were excited at 345 nm, corresponding to the sideband of SnO₂ nanocrystals, the emission of Eu³⁺ ions at 614 nm was clearly observed, while no emission of Eu³⁺ ions for the Eu³⁺‐doped sample. It may be ascribed to the energy transfer from SnO₂ conduction band to Eu³⁺ conduction band. Further experimental results suggest that the energy transfer may be achieved through surface transition state.     

Absorption and emission spectral studies of Eu3+-doped PbO-PbF2 glass system

Judd-Ofelt parameters obtained from the absorption spectra of Eu³⁺ ions doped in PbO-PbF₂ glasses are intermediate between the values for fluoride and phosphate glass matrices. Eu³⁺ ions are coordinated to both oxide and fluoride ions. The calculated transition probabilities (As^-1) for the laser transition⁵D_o→⁷F₂ are 171 and 170 for 30PbO-70PbF₂ and 70PbO-30PbF₂ glasses respectively and are significantly lower compared to phosphate glasses. The calculated (β_R cal) and experimental (β_Rexpt) branching ratios for this transition show good agreement. The emission spectra display high energy transitions in the 440–570 nm region, a characteristic of parent matrices with low energy phonons such as the tellurite, germanate and fluoride glasses. The electron-phonon coupling strengths deduced from the excitation spectra of Eu³⁺ are 10.2 x 10⁻³ and 9.5 x l0⁻³ for 30PbO-70PbF₂ and 70PbO-30PbF₂ glasses respectively. The relative emission intensities of the low energy transitions to high energy transitions and the ratios of the most intense transitions⁵D₀→⁷F₂/⁵D₀→⁷F₇ significantly vary for the two glasses providing evidence for clustering of Eu³⁺ ions with increase in its concentration and increasing PbO content.     

Eu3+ concentration dependent optical properties and energy transfer from host Gd3+ to Eu3+ in GdF3 nanocrystals

By using a hydrothermal method, a series of Eu³⁺ concentration dependent GdF₃ nanocrystals have been synthesized. The crystalline structures of samples are characterized by XRD patterns, the morphology and size of the samples are illustrated by FE-SEM images, and the optical properties of the samples are presented by PL excitation and emission spectra. The energy transfer from host Gd³⁺ to Eu³⁺ is observed in the Eu³⁺ doped GdF₃ nanocrystals. The optical properties of Eu³⁺ and the energy transfer efficiency from host Gd³⁺ to Eu³⁺ are discussed on the basis of the Eu³⁺ concentration dependent integrated PL excitation and emission spectra of Gd³⁺ and Eu³⁺. The discussion on optical properties of Eu³⁺ and the energy transfer from Gd³⁺ to Eu³⁺ is meaningful to design and synthesize Gd³⁺ based compounds.     

Novel Eu-doped lead telluroborate glasses for red laser source applications

We report the absorption, luminescence and decay analysis of Eu³⁺-doped lead telluroborate (PTBEu) glasses for different Eu³⁺ concentrations ranging from 0.1 to 2.0 mol%. Judd-Ofelt intensity parameters obtained from ⁵D₀→⁷F_J=0-6 emission transitions of Eu³⁺ were used to calculate the radiative transition probabilities, luminescence branching ratios and radiative decay times. The luminescence spectra and decay times were measured at 464 nm excitation. The optical band gap energies are also determined. The luminescence intensity ratio, color purity and emission cross-section values support that the PTBEu20 glass is a suitable candidate for red laser source applications.     

Luminescence in La3TaO4Cl6

The luminescence properties of La₃TaO₄Cl₆ are reported and discussed. The rare earth ions Sm³⁺, Eu³⁺, Tb³⁺, Dy³⁺, and Tm³⁺ show characteristic absorption and emission lines. For Sm³⁺ and Eu³⁺, broad absorption bands are also observed and are attributed to charge-transfer transitions. The line emissions of Tb³⁺ are only from ⁵D₄, even at low (1 at.%) concentration. Broad excitation and emission bands were observed with In³⁺. These bands are attributed to In³⁺Ta⁵⁺ → In⁴⁺Ta⁴⁺ charge-transfer transitions. An additional broad absorption at 250 and 280 nm leading to broad emission at 410 nm is ascribed to OH⁻ impurities.     

Synthesis of New LnxBi2–xSe3 (Ln: Sm3+, Eu3+, Gd3+, Tb3+) Nanomaterials and Investigation of Their Optical Properties

New Ln_xBi_2–xSe₃ (Ln: Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺) based nanomaterials were synthesized by a co‐reduction method. Powder XRD patterns indicate that the Ln_xBi_2–xSe₃ crystals (Ln = Sm³⁺, Eu³⁺, x = 0.00–0.44 and Ln = Gd³⁺, Tb³⁺, x = 0.00–0.50) are isostructural with Bi₂Se₃. The cell parameter c decreases for Ln = Eu³⁺, Gd³⁺, Tb³⁺ upon increasing the dopant content (x), while a slightly increases. Changes in lattice parameters could be related to the radii of cations. SEM images show that doping of the lanthanide ions in the lattice of Bi₂Se₃ generally results in nanoflowers. For the terbium compound two kinds of morphologies (nanoflowers and nanobelts) were observed. UV/Vis absorption and emission spectroscopy reveals mainly electronic transitions of the Ln³⁺ ions. Emission spectra show intense transitions from the excited to the ground state of Ln³⁺ and energy transfer from the Bi₂Se₃ lattice. Emission spectra of europium‐doped materials, in addition to the characteristic red emission peaks of Eu³⁺, show an intense blue emission band centered at 432 nm, originating from the 4f⁶5d¹ to 4f⁷ configuration in Eu²⁺. EPR measurements confirm the existence of Eu²⁺ in the materials. Interestingly, for all samples starting at low Ln³⁺ concentration, the emission intensity rises to a maximum at a Ln³⁺ concentration of x = 0.2 and falls again steadily to a minimum at x = 0.45.     

Homogeneous one-dimensional structured Tb(OH)3:Eu nanorods: Hydrothermal synthesis, energy transfer, and tunable luminescence properties

Nearly monodisperse, homogeneous and well-defined one-dimensional Tb_(1−x)(OH)₃:xEu³⁺ (x=0-3 mol%) nanorods have been prepared through hydrothermal method. The size of the Tb(OH)₃:Eu³⁺ rods could be modulated from nano- to micro-scale by using different amount of ammonia solution. They present highly crystallinity in spite of the moderate reaction temperature. Under ultraviolet excitation into the f→f transition of Tb³⁺ at 382 nm, Tb(OH)₃ samples show the characteristic emission of Tb³⁺ corresponding to ⁵D₄→⁷F_{6, 5, 4, 3} transitions; whereas Tb(OH)₃:Eu³⁺ samples mainly exhibit the characteristic emission of Eu³⁺ corresponding to ⁵D₀→⁷F_{1, 2, 4} transitions due to an efficient energy transfer occurs from Tb³⁺ to Eu³⁺. The increase of Eu³⁺ concentration leads to the increase of the energy transfer efficiency from Tb³⁺ to Eu³⁺. The PL colors of Tb(OH)₃:xEu³⁺ phosphors can be easily tuned from green, yellow, orange, to red by changing the doping concentration (x) of Eu³⁺.     

Photoluminescence properties of rare earths (Eu3+, Tb3+, Dy3+ and Tm3+) activated NaInW2O8 wolframite host lattice

The photoluminescence (PL) studies on NaIn_1?xRE_xW₂O₈, with RE=Eu³⁺, Tb³⁺, Dy³⁺ and Tm³⁺ phases have shown that the relative contribution of the host lattice and of the intra-f–f emission of the activators to the PL varies with the nature of the rare earth cation. In the case of Dy³⁺ and Tm³⁺ activators, with yellow and blue emission, respectively, the energy transfer from host to the activator plays a major role. In contrast for Eu³⁺, with intense red emission, the host absorption is less pronounced and the intra-f–f transitions of the Eu³⁺ ions play a major role, whereas for Tb³⁺ intra-f–f transitions are only observed, giving rise to green emission.