Preparation and up‐conversion luminescence properties of LaOBr:Yb3+/Er3+ nanofibers via electrospinning

LaOBr:Yb³⁺/Er³⁺ nanofibers were synthesized for the first time by calcinating electrospun PVP/[La(NO₃)₃ + Er(NO₃)₃ + Yb(NO₃)₃ + NH₄Br] composites. The morphology and properties of the final products were investigated in detail using scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X‐ray diffractometry (XRD) and fluorescence spectroscopy. The results indicate that LaOBr:Yb³⁺/Er³⁺ nanofibers are tetragonal in structure with a space group of P4/nmm. The diameter of LaOBr:Yb³⁺/Er³⁺ nanofibers is ~ 147 nm. Under the excitation of a 980‐nm diode laser, LaOBr:Yb³⁺/Er³⁺ nanofibers emit strong green and red up‐conversion emission centering at 519, 541 and 667 nm, ascribed to the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴ F_9/2 → ⁴I_15/2 energy‐level transitions of Er³⁺ ions, respectively. The up‐conversion luminescent mechanism of LaOBr:Yb³⁺/Er³⁺ nanofibers is advanced. Moreover, near‐infrared emission of LaOBr:Yb³⁺/Er³⁺ nanofibers is obtained under the excitation of a 532‐nm laser. The formation mechanism of LaOBr:Yb³⁺/Er³⁺ nanofibers is proposed. LaOBr:Yb³⁺/Er³⁺ nanofibers could be important up‐conversion luminescent materials. Copyright © 2014 John Wiley & Sons, Ltd.     

Pure red upconverted and near-infrared luminescence properties of Er3+-doped SnO2 nanocrystals for lighting applications

Tin oxide (SnO₂) nanocrystalline powders doped with erbium ion (Er³⁺) in different molar ratios (0, 3, 5, and 7 mol%) were prepared using a solid-state reaction technique. These samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible absorption, visible upconversion, and near-infrared luminescence techniques. XRD analysis revealed the tetragonal rutile structure of SnO₂ and the average crystallite size was about 32 nm. From Tauc's plots, it was confirmed that the substitution of Er³⁺ ions into the SnO₂ host lattice resulted in the narrowing its band gap. Optical absorption bands at 520 and 654 nm correspond to the 4f electron transitions of Er³⁺ further confirming visible light absorption. Infrared luminescence spectra showed a broad band centred at 1536 nm which is assigned to the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺. Visible upconverted emission spectra under 980 nm excitation exhibit a strong red luminescence with a main peak at 672 nm which is attributed to the ⁴F_9/2 → ⁴I_15/2 transition of Er³⁺. Power-dependent upconversion spectra confirmed that two photons participated in the upconversion mechanism. Enhancement in the intensities of both visible and infrared luminescence was observed when raising the concentration. The results pave the way for the potential applications of these nanocrystalline powders in energy harvesting applications such as infrared light upconverting layer in solar cells, light emitting diodes, infrared broadband sources and amplifiers, and biological labelling.     

Infrared and visible emissions of rare‐earth‐doped CeO2 phosphor

This paper reports the synthesis and characterization of Er³⁺‐doped CeO₂ phosphor with variable concentrations of erbium. The sample was synthesized using a solid‐state reaction method, which is useful for the large‐scale production of phosphors and is also eco‐friendly. The prepared sample was characterized using an X‐ray diffraction (XRD) technique. The XRD pattern confirmed that sample has the pure cubic fluorite crystal structure of CeO₂. The crystallite size of the prepared phosphor was determined by Scherer's formula and the crystallite size giving an intense XRD peak is 40.06 nm. The surface morphology of the phosphor was determined by field emission gun scanning electron microscopy (FEGSEM). From the FEGSEM image, good surface morphology with some agglomerates was found. The functional group in the prepared sample was analysed by Fourier transform infrared (FTIR) spectroscopy. All samples prepared with variable concentrations of Er³⁺ (0.1–2 mol%) were studied by photoluminescence analysis and it was found that the excitation spectra of the prepared phosphor shows broad excitation centred at 251 nm. Emission spectra at different concentrations of Er³⁺ show strong peaks at 413 and 470 nm and a weaker peak at 594 nm. The dominant peaks at 413 and 470 nm are caused by the allowed electronic transition ⁴S_3/2 → ⁴I_15/2 and the weaker transition at 594 nm is due to the transition ⁴ F_9/2 → ⁴I_15/2. Spectrophotometric determinations of peaks were evaluated using the Commission Internationale de I'Eclairage (CIE) technique. The emission spectra were also observed using an infrared (IR) laser 980 nm source, and three distinct peaks were found in the IR region at 848, 870 and 980 nm. The prepared phosphor has utility for application in display devices. Copyright © 2015 John Wiley & Sons, Ltd.     

Impact of ligand environment on optical,luminescence and thermometric behavior of A3(PO4)2:Sm3+ (A = Ca,Sr) phosphors

The present study investigates the impact of the ligand environment on the luminescence and thermometric behavior of Sm³⁺ doped A₃(PO₄)₂ (A = Sr, Ca) phosphors prepared by combustion synthesis. The structural and luminescent properties of Sm³⁺ ions in the phosphate lattices were investigated using powder X-ray diffraction (PXRD) and photoluminescence (PL) techniques. PXRD results of the synthesized phosphors exhibit the expected phases that are in agreement with their respective standards. Fourier-transform infrared (FTIR) spectroscopy confirms the presence of PO₄ vibrational bands. Upon excitation with near ultraviolet light, the PL studies indicated that Sr₃(PO₄)₂:Sm³⁺ phosphors exhibit a yellow light emission, whereas Ca₃(PO₄)₂:Sm³⁺ phosphors exhibit an emission of orange light. The PL emission results are in accordance with the CIE coordinates, with the Sr₃(PO₄)₂:Sm³⁺ phosphors showing coordinates of (0.56, 0.44), and the Ca₃(PO₄)₂:Sm³⁺ phosphors displaying coordinates of (0.60, 0.40). Thermal analysis shows improved stability of Ca₃(PO₄)₂:Sm³⁺ based on lower weight reduction in thermogravimetric analysis. The effect of temperature on the luminescence properties of the phosphor has been examined upon a 405 nm excitation. By using the fluorescence intensity ratio (FIR) method, the temperature responses of the emission ratios from the Sm³⁺: the ⁴F_3/2 → ⁶H_5/2 transition to the ⁴G_5/2 → ⁶H_7/2 and ⁴F_3/2 → ⁶H_5/2 transition to the ⁴G_5/2 → ⁶H_9/2 emissions are characterized. The Ca₃(PO₄)₂:Sm³⁺ phosphors are more sensitive as compared with the Sr₃(PO₄)₂:Sm³⁺ phosphors. The earlier research findings strongly indicate that these phosphors hold great promise as ideal candidates for applications in non-invasive optical thermometry and solid-state lighting devices.     

Optical analysis of RE3+ (RE = Nd or Er):B2O3–P2O5–CaF2–ZnO–(Li2O/Na2O/K2O) glasses

Calcium boro fluoro zinc phosphate glasses modified using alkali oxide and doped with Nd³⁺ and Er³⁺ ions with the chemical composition of 69.5 (B₂O₃) + 10 (P₂O₅) + 10 (CaF₂) + 5 (ZnO) + 5 (Na₂O/Li₂O/K₂O) + 0.5 (Er₂O₃/Nd₂O₃) were prepared using a conventional melt quenching technique. The results of X-ray diffraction patterns indicated the amorphous nature of all the prepared glasses. The visible–near-infrared red (NIR) absorption spectra of these glasses were analyzed systematically. The NIR emission spectra of Er³⁺ and Nd³⁺:calcium boro fluoro zinc phosphate glasses showed prominent emission bands at 1536 nm (⁴I_13/2→⁴I_15/2) and 1069 nm (⁴F_3/2→⁴I_11/2) respectively with λ_exci = 514.5 nm (Ar⁺ laser) as the excitation source.     

Erbium(III) ion-doped borate-based glasses for 1.53 μm broad band applications

Novel erbium(III) ion-doped borate-based glasses (Er³⁺:BCNF) by conventional melt-quenching technique were designed and synthesized. The glasses were characterized for their structural, vibrational and spectroscopic properties. The nephelauxetic ratio, bonding parameters, and Judd–Ofelt (JO) intensity parameters (Ω_λ λ = 2, 4 and 6) were determined by using absorption spectrum of 1 mol% Er₂O₃ doped glass. These JO parameters were utilized to derive radiative properties for various excited states of erbium(III) ions. Emission cross-section for ⁴I_13/2 → ⁴I_15/2 transition of erbium(III) ions was computed through McCumber theory. The decay curves for (²H_11/2, ⁴S_3/2) and ⁴I_13/2 levels were recorded and analysed. All the results of Er³⁺:BCNF glasses revealed that the studied glasses are efficient and thermally stable and could be suitable for display devices, optical amplification and green laser applications.     

Near-field enhancement of infrared intensities for <Emphasis Type="Italic">f-f</Emphasis> transitions in Er<Superscript>3+</Superscript> ions close to the surface of silicon nanoparticles

Erbium doped waveguide amplifiers can be used in optical integrated circuits to compensate for signal losses. Such amplifiers use stimulated emission from the first excited state (⁴ I _13/2) to the ground state (⁴ I _15/2) of Er³⁺ at 1.53 μm, the standard wavelength for optical communication. Since the intra-f transitions are parity forbidden for free Er³⁺ ions, the absorption and the emission cross sections are quite small for such doped amplifiers. To enhance the absorption, Si nanoclusters can be embedded in silica matrix. Here we investigate the effect of the Si nanocluster on the Er³⁺ emission using ab initio theory for the first time. We combine multi-reference configuration interaction with one-electron spin-orbit Hamiltonian and relativistic effective core potentials. Our calculations show that the presence of a polarizable Be atom at 5Ǻ from the Er³⁺ ion in a crystalline environment can lead to an enhancement in the emission by a factor of three. The implications of this effect in designing more efficient optical gain materials are discussed.     

Photoluminescence properties of aeschynite‐type LaNbTiO6:RE3+ (RE = Tb,Dy, Ho) down‐converting phosphors

In this study, a series of LaNbTiO₆:RE³⁺ (RE = Tb, Dy, Ho) down‐converting phosphors were synthesized using a modified sol–gel combustion method, and their photoluminescence (PL) properties were investigated as a function of activator concentration and annealing temperature. The resultant particles were characterized using X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, UV/Vis diffuse reflectance spectroscopy and PL spectra. The highly crystalline LaNbTiO₆:RE³⁺ (RE = Tb, Dy, Ho) phosphors with an average size of 200–300 nm obtained at 1100°C have an orthorhombic aeschynite‐type structure and exhibit the highest luminescent intensity in our study range. The emission spectra of LaNbTiO₆:RE³⁺ (RE = Tb, Dy, Ho) phosphors under excitations at UV/blue sources are mainly composed of characteristic peaks arising from the f–f transitions of RE³⁺, including 489 nm (⁵D₄ → ⁷F₆) and 545 nm (⁵D₄ → ⁷F₅) for Tb³⁺, 476 and 482 nm (⁴F_9/2 → ⁶H_15/2) and 571 nm (⁴F_9/2 → ⁶H_13/2) for Dy³⁺, and 545 nm (⁵F₄ + ⁵S₂ → ⁵I₈) for Ho³⁺, respectively. The luminescent mechanisms were further investigated. It can be expected that these phosphors are of intense interest and potential importance for many optical applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Spectral‐converting study of Ba9–3(m+n)/2ErmYbnY2Si6O24 (m = 0.005 – 0.2, n = 0 – 0.3) orthosilicate phosphors

Optical materials composed of Ba_9–3(m+n)/2Er_mYb_nY₂Si₆O₂₄ (m = 0.005–0.2, n = 0–0.3) were prepared using a solid‐state reaction. The X‐ray diffraction patterns of the obtained phosphors were examined to index the peak positions. The photoluminescence (PL) excitation and emission spectra of the Er³⁺‐activated phosphors and the critical emission quenching as a function of Er³⁺ content in the Ba_9–3m/2Er_mY₂Si₆O₂₄ structure were monitored. The spectral conversion properties of Er³⁺ and Er³⁺–Yb³⁺ ions doped in Ba₉Y₂Si₆O₂₄ phosphors were elucidated under diode‐laser irradiation at 980 nm. Up‐conversion emission spectra and the dependence of the emission intensity on pump power for the Ba_8.55Er_0.1Yb_0.2Y₂Si₆O₂₄ phosphor were investigated. The desired up‐conversion of the emitted light, which passed through the green, yellow, orange and red regions of the spectrum, was achieved through the use of appropriate Er³⁺ and/or Yb³⁺ concentrations in the host structure and 980 nm excitation light. The up‐conversion mechanism in the phosphors is described by an energy‐level schematic. Copyright © 2015 John Wiley & Sons, Ltd.     

Facile synthesized NaGdF4:Yb,Er peanut-shaped,highly biocompatible,colloidal upconversion nanospheres

A facile method was used for the synthesis of peanut-shaped very emissive NaGdF₄:Yb, Er upconversion nanospheres (UCNSs) at lower temperatures with uniform size distribution. Crystallographic structure, phase purity, morphology, thermal robustness, biocompatibility, colloidal stability, surface chemistry, optical properties, and luminesce properties were explored by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), zeta potential, thermogravimetric/differential thermal analysis (TGA/DTA), Fourier-transform infrared (FTIR), ultraviolet (UV)-visible and photoluminescence spectroscopic tools. XRD pattern verified the construction of a single-phase, highly-crystalline NaGdF₄ phase with a hexagonal structure. Peanut-shaped morphology of the sample was obtained from SEM micrographs which were validated from high-resolution TEM images, to have an equatorial diameter of 170 to 200 nm and a length of 220 to 230 nm, with irregular size, monodispersed, porous structure, and rough surface of the particles. The positive zeta potential value exhibited good biocompatibility along with high colloidal stability as observed from the absorption spectrum. The prepared UCNSs revealed high dispersibility, irregular size peanut-shaped morphology, rough surface, good colloidal stability, and excellent biocompatibility in aqueous media. A hexagonal phase NaGdF₄ doped with ytterbium (Yb) and erbium (Er) UCNSs revealed the characteristics of highly dominant emissions located at 520–525, 538–550, and 659–668 nm corresponding to the ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, and ⁴F_9/2 → ⁴I_15/2 transition of Er³⁺ ions, respectively, as a result of energy transfer from sensitizer Yb³⁺ ion to emitter Er³⁺ ion.     

Effect of Dy3+ or Eu2+ co‐activator on a BaCa(SO4)2:Ce3+ mixed alkaline earth sulfate phosphor

The individual emission and energy transfer between Ce³⁺ and Eu²⁺ or Dy³⁺ in BaCa(SO₄)₂ mixed alkaline earth sulfate phosphor prepared using a co‐precipitation method is described. The phosphor was characterized by X‐ray diffraction (XRD) and photoluminescence (PL) studies and doped by Ce;Eu and Dy rare earths. All phosphors showed excellent blue–orange emission on excitation with UV light. PL measurements reveal that the emission intensity of Eu²⁺ or Dy³⁺ dopants is greater than when they are co‐doped with Ce³⁺. An efficient Ce³⁺ → Eu²⁺ [²T_2g(4f⁶5d) → ⁸S_7/2(4f₇)] and Ce³⁺ → Dy³⁺ (⁴ F_9/2 → ⁶H_15/2 and ⁴ F_9/2 → ⁶H_13/2) energy transfer takes place in the BaCa(SO₄)₂ host. A strong blue emission peak was observed at 462 nm for Eu²⁺ ions and an orange emission peak at 574 nm for Dy³⁺ ions. Hence, this phosphor may be used as a lamp phosphor. Copyright © 2015 John Wiley & Sons, Ltd.     

Photoluminescence and thermoluminescence properties of pure and rare-earth-doped ZrO2 prepared by Pechini-type sol–gel

In this article, photoluminescence (PL) and thermoluminescence (TL) properties of ZrO₂, ZrO₂:Dy³⁺, ZrO₂:Dy³⁺–Gd³⁺, ZrO₂:Dy³⁺–Yb³⁺, ZrO₂:Dy³⁺–Er³⁺, and ZrO₂:Dy³⁺–Sm³⁺ phosphors synthesized by the Pechini method were investigated. The crystal structure, thermal properties, morphology, PL and TL properties were investigated using X-ray powder diffraction (XRD), differential thermal analysis/thermogravimetric analysis (DTA/TGA), scanning electron microscopy (SEM), PL and TL, respectively. The room temperature emission bands corresponding to ⁴F_9/2 → ⁶H_J (J = 9/2, 11/2, 13/2 and 15/2) transitions of Dy³⁺ ions were measured. The phosphors were analysed using T_m–T_STOP, variable dose, and computerized glow curve fitting methods. Reusability, dose–response, and fading characteristics were investigated. The phosphors have a natural TL emission that vanished by heating treatment. Moreover, new peaks with similar properties to the natural emissions were observed after high-dose irradiation and long-term fading experiments. The glow curves of the phosphors have 13 individual peaks and many low- and high-temperature satellite peaks. The origin of the peaks is ZrO₂ host material and doping with rare-earth ions (Gd³⁺, Dy³⁺, Yb³⁺, Er³⁺ and Sm³⁺) does not lead to a new glow peak. The dopants cause drastic changes in individual peak intensities of ZrO₂.The initial fading rates of all the phosphors are relatively fast, but they slow down as time goes on.     

Effect of Bi3+ addition on the upconversion luminescence properties of NaYbF4:Er

In this study, Bi³⁺ incorporation in NaYbF₄:Er lattice and its influence on upconversion luminescence properties have been investigated in detail using techniques such as temperature‐dependent luminescence, Fourier transform infrared spectroscopy and X‐ray diffraction (XRD). The study was carried out to develop phosphors with improved upconversion luminescence. From photoluminescence and lifetime measurements it is inferred that luminescence intensity from NaYbF₄:Er increases with Bi³⁺ addition. The sample containing 50 at.% Bi³⁺ ions exhibited optimum upconversion luminescence. Increased distance between Yb³⁺–Yb³⁺ and Er³⁺–Er³⁺ due to Bi³⁺ incorporation into the lattice and associated decrease in the extent of dipolar interaction/self‐quenching are responsible for increase in lifetime values and luminescence intensities from Er³⁺ ions. Incorporation of Bi³⁺ into NaYbF₄:Er lattice reduced self‐quenching among Yb³⁺–Yb³⁺ions and this facilitated energy transfer from Yb³⁺ to Er³⁺. This situation also explains decrease in the extent of temperature‐assisted quenching of emission from thermally coupled ²H_11/2 and ⁴S_3/2 levels of Er³⁺. Based on Rietveld refinement of XRD patterns it was confirmed that a maximum of 10 at.% of Bi³⁺added was incorporated into the NaYbF₄:Er lattice and the remaining complex co‐exists as a BiOF phase. These results are of significant interest in the area of development of phosphors based on Yb³⁺–Er³⁺ upconversion luminescence.     

A novel reddish‐orange phosphor,NaLi2PO4:Eu3+

A series of Eu³⁺‐activated NaLi₂PO₄ novel phosphors was synthesized by the solid‐state reaction method. The X‐ray diffraction (XRD) and photoluminescence (PL) properties of these phosphors were investigated at room temperature. The excitation spectra indicate that these phosphors can be effectively excited by near‐UV (370–410 nm) light. The emission spectra exhibit strong reddish‐orange performance, which is due to the ⁵D₀ → ⁷F_J transitions of Eu³⁺ ions. The orange emission from transition ⁵D₀ → ⁷F₁ is dominant over that of ⁵D₀ → ⁷F_2. The concentration quenching of Eu³⁺ was observed in NaLi₂PO₄:Eu³⁺ when the Eu concentration was at 1 mol%. The impact of doping Eu³⁺ and photoluminescence properties were investigated and we propose a feasible interpretation. Copyright © 2012 John Wiley & Sons, Ltd.     

Photoluminescence properties of LiBaPO4:M3+ phosphor for near‐UV light‐emitting diode (M = Eu and Dy)

A novel phosphor LiBaPO₄ doped with rare earths Eu and Dy prepared by high temperature solid‐state reaction method is reported. The phosphors were characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). The emission and excitation spectra of these materials were measured at room temperature with a spectrofluorophotometer. The excitation spectra of LiBaPO₄:Eu³⁺ phosphor can be efficiently excited by 394 nm, which is matched well with the emission wavelength of near‐UV light‐emitting diode (LED) chip. PL properties of Eu³⁺‐doped LiBaPO₄ exhibited the characteristic red emission coming from ⁵D₀ → ⁷ F₁ (593 nm) and ⁵D₀ → ⁷ F₂ (617 nm) electronic transitions with color co‐ordinations of (0.680, 0.315). The results demonstrated that LiBaPO₄:Eu³⁺ is a potential red‐emitting phosphor for near‐UV LEDs. Emission spectra of LiBaPO₄:Dy³⁺ phosphors showed efficient blue (481 nm) and yellow (574 nm) bands, which originated from ⁴ F_9/2 → ⁶H_15/2 and ⁴ F_9/2 → ⁶H_13/2 transitions of the Dy³⁺ ion, respectively. The 574 nm line is more intense than the 481 nm lines, which indicates that the site Dy³⁺ is located with low symmetry. This article summarizes fundamentals and possible applications of optically useful inorganic phosphates with visible photoluminescence of Eu³⁺ and Dy³⁺ ions. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and luminescence of novel near‐infrared emitting BaZrSi3O9:Cr3+ phosphors

The BaZrSi₃O₉:Cr³⁺ phosphors were prepared by a high temperature solid state method. Their structures were confirmed with XRD and their luminescence properties were investigated. Under excitation at 455 nm, BaZrSi₃O₉:Cr³⁺ phosphors exhibited a broad near infrared emission band peaked at 800 nm, which was assigned to the ⁴T₂→⁴A₂ transition of Cr³⁺. The near infrared emission intensity reached a maximum at Cr³⁺ concentration of 0.7%. There was a concentration quenching phenomenon of Cr³⁺ in BaZrSi₃O₉ matrix and the corresponding concentration quenching mechanism was investigated. With efficient near infrared emission in the range of 700–1000 nm, BaZrSi₃O₉:Cr³⁺ phosphors may find applications in solar energy conversion.     

Luminescence study of Dy or Ce activated LiCaBO3 phosphor for γ‐ray and C5+ ion beam irradiation

The photoluminescence and thermoluminescence characteristics of rare earths (Dy or Ce) activated LiCaBO₃ phosphors have been studied. Phosphors were synthesized by modified solid state synthesis. The phosphors were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) and thermoluminescence (TL) for structural, morphological and luminescence studies. Dy³⁺ activated LiCaBO₃ shows emission at 486 and 577 nm due to ⁴ F_9/2 → ⁶H_15/2 and ⁴ F_9/2 → ⁶H_13/2 transition, respectively, whereas the PL emission spectra of Ce³⁺ activated LiCaBO₃ phosphor shows a broad band peaking at 432 nm, which is due to the transition from 5d level to the ground state of the Ce³⁺ ion. The thermoluminescence study was also carried out for both these phosphors for γ‐ray irradiation and carbon beam irradiation. Linearity was studied for a 0.4–3.1 Rad dose γ‐rays. Linear behaviour over this dose range was observed. Gamma ray‐irradiated phosphors were shown to be negligible fading upon storage. All the samples were also studied for 75 MeV C⁵⁺ ion beam exposure in the range of 3.75 × 10¹² – 7.5 × 10¹³ ion cm^–2 fluence. In addition to this, trapping parameters of all the samples were also calculated using Chen's peak shape method. Copyright © 2015 John Wiley & Sons, Ltd.     

Enhanced luminescence and white light emission from Eu3+‐co‐doped K3Ca2(SO4)3Cl:Dy3+ phosphor with near visible ultraviolet excitation for white LEDs

The luminescent properties of europium (Eu)‐ and dysprosium (Dy)‐co‐doped K₃Ca₂(SO₄)₃Cl halosulfate phosphors were analyzed. This paper reports the photoluminescence (PL) properties of K₃Ca₂(SO₄)₃Cl microphosphor doped with Eu and Dy and synthesized using a cost‐effective wet chemical method. The phosphors were characterized by X‐ray diffraction and scanning electron microscopy. The CIE coordinates were calculated to display the color of the phosphor. PL emission of the prepared samples show peaks at 484 nm (blue), 575 nm (yellow), 594 nm (orange) and 617 nm (red). The emission color of the Eu,Dy‐co‐doped K₃Ca₂(SO₄)₃Cl halophosphor depends on the doping concentration and excitation wavelength. The addition of Eu in K₃Ca₂(SO₄)₃Cl:Dy greatly enhances the intensity of the blue and yellow peaks, which corresponds to the ⁴ F_9/2 → ⁶H_15/2 and ⁴ F_9/2 → ⁶H_13/2 transitions of Dy³⁺ ions (under 351 nm excitation). The Eu³⁺/Dy³⁺ co‐doping also produces white light emission for 1 mol% of Eu³⁺, 1 mol% of Dy³⁺ in the K₃Ca₂(SO₄)₃Cl lattice under 396 nm excitation, for which the calculated chromaticity coordinates are (0.35, 0.31). Thus, K₃Ca₂(SO₄)₃Cl co‐doped with Eu/Dy is a suitable candidate for NUV based white light‐emitting phosphors technology. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and luminescence properties of Ca3Ga2Si3O12:RE3+ (RE = Eu/Tb) powder phosphors

Rare earth ions (Eu³⁺ or Tb³⁺)‐activated Ca₃ Ga₂ Si₃O₁₂ (CaGaSi) phosphors were synthesized by using a sol–gel method. Photoluminescence spectra of Eu³⁺:CaGaSi phosphors exhibited five emission bands at 578, 592, 612, 652 and 701 nm, which were assigned to the transitions (⁵D₀ → ⁷F₀, ⁷F_1, ⁷F₂, ⁷F₃ and ⁷F₄), respectively, with an excitation wavelength of λ_exci = 392 nm. Among these, the transition ⁵D₀ → ⁷F₂ (612 nm) displayed bright red emission. In the case of Tb³⁺:CaGaSi phosphors, four emission bands were observed at 488 (⁵D₄ → ⁷F₆), 543 (⁵D₄ → ⁷F₅), 584 (⁵D₄ → ⁷F₄) and 614 nm (⁵D₄ → ⁷F₃) from the measurement of PL spectra with λ_exci = 376 nm. Among these, the transition ⁵D₄ → ⁷F₅ at 543 nm displayed bright green emission. The structure and morphology of the phosphors were studied from the measurements of X‐ray diffraction (XRD), scanning electron microscopy (SEM) and energy‐dispersive X‐ray analysis (EDAX) results. Copyright © 2011 John Wiley & Sons, Ltd.     

The uncatalysed and the copper(II) promoted hydrolysis of 4-nitrophenyl L-leucinate

The uncatalysed hydrolysis of 4-nitrophenyl L-leucinate has been studied in detail over a range of pH and temperature at I=0.1 M (KNO₃). Base hydrolysis of the ester is strongly promoted by copper(II) ions. Rate constants have been obtained for the following reactions (where EH⁺ is the N- protonated ester and E is the free base form) EH⁺ + OH⁻ → products E + OH⁻ → products E + H₂O → products CuE²⁺ + OH⁻ → products Base hydrolysis of the copper(II) complex CuE²⁺ is 3.8 × 10⁵ times faster than that of E and 75 times faster than that of EH⁺ at 25 °C and I=0.1 M. Activation parameters for these reactions have been determined and possible mechanisms are considered.