Effect of flux on the properties of CaAl2O4:Eu, Nd long afterglow phosphor

The long afterglow phosphor CaAl₂O₄:Eu²⁺, Nd³⁺was prepared by high temperature solid-state reaction method under reducing atmosphere. The effect of flux H₃BO₃ on the crystal structure and luminescent properties of the phosphor was studied. Results of XRD indicate that the volume of unit cell becomes smaller, and then the crystal field is changed, which results in the easier transition of 4f-5d. On the other hand, H₃BO₃ addition is in favor of the formation of pure phase CaAl₂O₄. Both behaviors enhance the emission intensity of the obtained phosphor to some extent. But its emission peak does not shift evidently because the energy level difference of 4f-5d does not be changed obviously. Moreover, H₃BO₃ also affects the afterglow properties of this phosphor. The optimized content of H₃BO₃ is 0.06 mol/mol for the obtained phosphor with excellent properties.     

Spectral and kinetic characterization of orange-red emitting Sr3Al2O6:Eu/Smphosphor

We report, for the first time Sm³⁺ doped nanocrystalline Sr₃Al₂O₆ phosphor. Effect of Eu³⁺ doping in the present host is also studied. XRD results match with standard data from JCPDS file confirming cubic structure with Pa3 space group. PL Maximum for Eu/Sm is obtained at 590 nm and 573 nm respectively, and corresponds to orange-red region of electromagnetic spectrum. Morphology of combustion synthesized powder is platelet, while for calcined powders, cubic shaped crystallites are obtained. Information on various trapping parameters is obtained from thermally stimulated Luminescence (TSL) studies. Non-shifting T_m property is applied to define the order of kinetics and is thereafter assumed as 1. T_m − T_stop procedure and repeated initial rise method are applied to estimate apparent activation energies and peak positions. Further, chi-square minimization procedures via computerized glow curve deconvolution (CGCD) technique provide best-fit results. The figure of merit for deconvoluted Eu and Sm doped samples are 0.48% and 0.67% respectively. The apparent activation energies for Eu doped samples are 0.89 eV, 1.05 eV, 1.30 eV, while, for Sm doped samples, the activation energies are 0.84 eV and 1.06 eV. Persistence behavior of the present phosphor is attributed to contribution due to shorter and longer components as are obtained during phosphorescence decay studies. In both the cases; probability of recombination is more in comparison to the retrapping within a quasi continuous framework of trapping sites.     

Influence of La and Dy on the properties of the long afterglow phosphor CaAl2O4: Eu, Nd

The long afterglow phosphor CaAl₂O₄:Eu²⁺,Nd³⁺ was prepared by the high temperature solid-state reaction method, and the influence of La³⁺ and Dy³⁺ on the properties of the long afterglow phosphor was studied by X-ray diffraction (XRD), photoluminescence (PL), and thermoluminescence (TL). The XRD pattern shows the host phase of CaAl₂O₄ is produced and no impurity phase appears. The peak wavelength of the phosphor does not vary with La³⁺ and Dy³⁺ doping. It implies that the crystal field, which affects the 5d electron states of Eu²⁺, is not changed dramatically after doping of La³⁺ and Dy³⁺. The TL spectra indicate that the phosphor doped with La³⁺ or Dy³⁺ produces different depths of trap energy level. In the mechanism of long afterglow luminescence, it is considered that La³⁺ or Dy³⁺ works as trap energy level. The decay time lies on the number of electrons in the trap energy level and the rate of the electrons returning to the excitation level.     

Investigation on the enhancement and the suppression of persistent luminescence of Re doped Sr2EuMgSi2O7 (Re = Dy, Yb)

The enhancement and the suppression of persistent luminescence on Sr₂EuMgSi₂O₇ are investigated by Dy³⁺ or Yb³⁺ doping. The TL curves show the deep traps induced by Yb³⁺ besides the intrinsic traps. The TL intensity of deep traps is stable whereas it decreases with preheating, indicating a charge carriers transfer process from the intrinsic traps to the deep ones. The mean lifetime of charge carriers in the deep traps is longer because of greater activation energy, restraining the detrapping. The similar process dominates the Dy³⁺ doped sample with an optimum trap depth, resulting in the enhancement of persistence luminescence.     

Preparation and structural properties of Lu2O3:Eu submicrometer spherical phosphors

Monodisperse non-agglomerated Lu₂O₃:Eu³⁺ submicrometer spheres were obtained by the homogeneous precipitation technique with subsequent annealing for spheres crystallization. The morphological and structural parameters of the Lu₂O₃:Eu³⁺ crystalline spheres prepared were investigated by the electron microscopy methods, thermal analysis (TG-DTA), X-ray diffractometry (XRD), X-ray photoelectron (XPS) and FT-IR spectroscopy. The influence of the annealing temperature on the morphology and sphericity was shown. Eu³⁺-doped lutetium oxide spheres were characterized by effective luminescence under X-ray excitation in the λ = 575-725 nm range corresponding to ⁵D₀ → ⁷F_J transitions (J = 0-4) of Eu³⁺ ions. It was shown that the X-ray luminescence efficiency of the Lu₂O₃:Eu³⁺ spherical phosphors prepared strongly depend on annealing temperature and dopant concentration.     

Synthesis, crystal structure and X-ray excited luminescent properties of LuBa3B9O18

A new compound LuBa₃B₉O₁₈ has been prepared by a high-temperature solid-state reaction and its crystal structure was determined by powder X-ray diffraction methods. The results of Rietveld refinement show that it is isotypic to YBa₃B₉O₁₈. The X-ray excited luminescent properties of LuBa₃B₉O₁₈ were investigated. It shows a broad emission band in the wavelength range of 300–550 nm with peak center at 385 nm. Its room temperature fluorescent decay profile exhibits a single-exponent shape with decay time of 15 ns. It is believed that the lattice defects have played an important role on the luminescent performances of LuBa₃B₉O₁₈ powders and its thermal luminescence measurement confirmed the existence of lattice defects in it. Considering the emission wavelength, luminescence intensity, decay time, melting point, density and non-hygroscopic property of LuBa₃B₉O₁₈, one has reason to assume that it might find an application as a new scintillation material.     

Cr doping optimization in CaAl2O4:Eu blue phosphor

A new composition of phosphor material CaAl₂O₄:Eu²⁺ co-doped with Cr³⁺ was investigated. Various compositions with Eu²⁺ (1 and 2 mol%) and Cr³⁺ (0.05–0.1 mol%) were prepared by solid-state reaction method. These compositions show high brightness and longer persistent luminescence. Phase and crystallinity were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Excitation and emission spectra were taken to investigate the luminescence characteristics. Broad band UV excited luminescence of the CaAl₂O₄:Eu²⁺, Cr³⁺ was observed in the blue region (λ_max = 440 nm) due to transitions from 4f⁶5d¹ to the 4f⁷ configuration of the Eu²⁺ ion. Cr³⁺ ion co-doping generates deep traps which results in longer afterglow phosphorescence compared to parent phosphor.     

Synthesis, photoluminescence, thermoluminescence and dosimetry properties of novel phosphor KSr4(BO3)3:Ce

Polycrystalline powder sample of KSr₄(BO₃)₃ was synthesized by high-temperature solid-state reaction. The influence of different rare earth dopants, i.e. Tb³⁺, Tm³⁺ and Ce³⁺, on thermoluminescence (TL) of KSr₄(BO₃)₃ phosphor was discussed. The TL, photoluminescence (PL) and some dosimetric properties of Ce³⁺-activated KSr₄(BO₃)₃ phosphor were studied. The effect of the concentration of Ce³⁺ on TL intensity was investigated and the result showed that the optimum Ce³⁺ concentration was 0.2 mol%. The TL kinetic parameters of KSr₄(BO₃)₃:0.002 Ce³⁺ phosphor were calculated by computer glow curve deconvolution (CGCD) method. Characteristic emission peaking at about 407 and 383 nm due to the 4f⁰5d¹ → ²F_{(5/2, 7/2)} transitions of Ce³⁺ ion were observed both in PL and three-dimensional (3D) TL spectra. The dose–response of KSr₄(BO₃)₃:0.002 Ce³⁺ to γ-ray was linear in the range from 1 to 1000 mGy. In addition, the decay of the TL intensity of KSr₄(BO₃)₃:0.002 Ce³⁺ was also investigated.     

Optical study of a new phase LaGa3O6:RE (RE=Pr, Nd, Eu) in the La2O3–Ga2O3 system

The absorption and emission spectroscopies of RE³⁺ ions embedded in a new phase, LaGa₃O₆, owing to the La₂O₃–Ga₂O₃ binary system (RE=Pr, Nd, Eu) are discussed. The ^2S+1L_J level degeneracies are completely lifted in accordance with the low point symmetry of the site occupied by the rare earth ion in LaGa₃O₆. The energy level schemes deduced from the data are reproduced by considering a crystal field (CF) effective Hamiltonian involving the nine real and five imaginary parameters required for the C₂ or C_s symmetry of the rare earth site. The rms deviation is satisfactory for the three simulations. However, the strong variation of the CF parameters between Pr³⁺ and Eu³⁺ in LaGa₃O₆ suggests the possible limit of existence of the phase, intimately correlated to small variations of the rare earth ionic radius.     

Photoluminescence and thermoluminescence studies of Mg2SiO4:Eu nano phosphor

Nanoparticles of Eu³⁺ doped Mg₂SiO₄ are prepared using low temperature solution combustion technique with metal nitrate as precursor and urea as fuel. The synthesized samples are calcined at 800 °C for 3 h. The Powder X-ray diffraction (PXRD) patterns of the sample reveled orthorhombic structure with α-phase. The crystallite size using Scherer's formula is found to be in the range 50-60 nm. The effect of Eu³⁺ on the luminescence characteristics of Mg₂SiO₄ is studied and the results are presented here. These phosphors exhibit bright red color upon excitation by 256 nm light and showed the characteristic emission of the Eu³⁺ ions. The electronic transition corresponding to ⁵D₀ → ⁷F₂ of Eu³⁺ ions (612 nm) is stronger than the magnetic dipole transition corresponding to ⁵D₀ → ⁷F₁ of Eu³⁺ ions (590 nm). Thermoluminescence (TL) characteristics of γ-rayed Mg₂SiO₄:Eu³⁺ phosphors are studied. Two prominent and well-resolved TL glows with peaks at 202 °C and 345 °C besides a shoulder with peak at ∼240 °C are observed. The trapping parameters-activation energy (E), order of kinetics (b) and frequency factor (s) are calculated using glow curve shape method and the results obtained are discussed.     

Synthesis and properties of Ba3NaRu2O9−δ and Ba3(Na, R)Ru2O9−δ (R=rare earth) crystals

Crystals of Ba₃NaRu₂O_9−δ (δ≈0.5) and Ba₃(Na, R)Ru₂O_9−δ (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6₃mmc. Ba₃NaRu₂O_9−δ and Ba₃(Na, R)Ru₂O_9−δ (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba₃NaRu₂O_9−δ has an effective magnetic moment P_eff of 0.91 μ_B, while P_eff of Ba₃(Na, R)Ru₂O_9−δ (except Ce) reflects the large free-ion moment of the rare earth ions. Ba₃(Na, Ce)Ru₂O_9−δ shows peculiar magnetic behavior that differs from the magnetism of other Ba₃(Na, R)Ru₂O_9−δ crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.10.2 eV.     

Luminescent properties of CaMgSi2O6 and Ca2MgSi2O7 phosphors activated by Eu, Dyand Nd

Long lasting alkaline earth silicates, CaMgSi₂O₆:Eu,Dy,Nd, Ca₂MgSi₂O₇:Eu,Dy,Nd and Ca₂MgSi₂O₇:Eu,Dy, were prepared under a reducing atmosphere by a solid-state reaction. The obtained phosphors were characterized by means of X-ray diffraction (XRD) and their photoluminescence spectrum (PLS). The Ca₂MgSi₂O₇:Eu,Dy,Nd phosphor showed a two-peak emission at 447 and 516 nm, while the CaMgSi₂O₆:Eu,Dy,Nd phosphor generated only one peak emission at 447 nm. This phenomenon is due to the different lattice sites occupied by Eu²⁺ in the Ca₂MgSi₂O₇ and CaMgSi₂O₆ lattices. The electron affinity (ea) values for Eu²⁺ in [EuO₆] and [EuO₈] were calculated to be 4.2 and 1.9 eV, respectively. The Nd co-doped phosphor revealed a better afterglow characteristic, indicating that a deeper trap center was formed in the phosphor by the doping of trivalent Nd ions.     

The reduction of Eu to Eu in air and luminescence properties of Eu activated ZnO–B2O3–P2O5 glasses

A valence change from Eu³⁺ to Eu²⁺ was observed in the europium ion-doped ZnO–B₂O₃–P₂O₅ glasses prepared at high temperature in air. The fluorescence emission spectrum of the sample consists of a broad emission band ascribed to the 5d–4f transition of Eu²⁺ ion and sharp emission peaks assigned to the transitions of ⁵D_o–⁷F_J (J = 0, 1, 2, 3, and 4) of Eu³⁺ ion, indicating that part of Eu³⁺ can be reduced into Eu²⁺ in the glass. A charge compensation model is proposed. The rigid tetrahedral network structure of glasses plays an important role in stability of Eu²⁺. The fabrication conditions are also studied.     

Optical and structural characterisation of pure and Pr doped LaPO4 and CePO4 nanocrystals

The rod- and stick-shaped nanocrystalline cerium and lanthanum orthophosphates, pure and Pr³⁺ doped, have been synthesised by the hydrothermal method in acidic (pH 1) or alkaline (pH 11) environment. Subsequent calcination of as-obtained powders at different temperatures, 500 and 900 °C, led to the formation of hexagonal and monoclinic phases, respectively. The hexagonal phase at room temperature has been identified as hydrated orthophosphate with zeolite water inside the channels of the structure. The monoclinic phase is free of water.The average grain size is about 12-30 nm depending on the calcination temperature and preparation conditions. The structural, morphological and optical (vibrational and luminescent) properties have been characterised and their changes due to the temperature and different acidity in the starting materials have been studied.     

Luminescent properties of Sr2MgSi2O7 and Ca2MgSi2O7 long lasting phosphors activated by Eu, Dy

Long lasting afterglow phosphors Sr₂MgSi₂O₇:Eu,Dy and Ca₂MgSi₂O₇:Eu,Dy were prepared by solid-state reaction method. It is revealed by the results that both phosphors show two emission peaks that are caused by the different emitting centers Eu²⁺ held in the host lattice. Wavelength shift was observed due to the slight differences in the structure parameters of the two hosts. Investigation on afterglow property shows that Sr₂MgSi₂O₇:Eu,Dy phosphor held a better afterglow property than Ca₂MgSi₂O₇:Eu,Dy phosphor. Thermal simulated luminescence study indicates that the long afterglow is generated by a higher trap concentration formed by the co-doped rare earth ions within the host.     

Thermoelectric properties of Ni- and Zn-doped Nd2CuO4

The electrical resistivity, Seebeck coefficient, and thermal conductivity of Nd₂(Cu_0.98M_0.02)O₄ (M: Ni and Zn) have been measured in the temperature range from room temperature to about 1000 K. Ni- and Zn-doping decreases the electrical resistivity and the absolute values of the Seebeck coefficient. The thermal conductivity decreases with increasing temperature, showing phonon conduction, and also decreases by doping. The power factor of Nd₂(Cu_0.98Ni_0.02)O₄ reaches 1.02×10⁻⁴ W m⁻¹ K⁻² and the figure of merit is 1.35×10⁻⁵ K⁻¹ at 320 K. The relatively low figure of merit compared with that of the state-of-the-art thermoelectric materials is due to the high thermal conductivity.     

Magnetic structures of rare earths R in RCoC2 and RNiC2 compounds

A comparative survey is given on the variety of magnetic structures of the series of RCoC₂ and RNiC₂ with R=Pr, Nd, Tb, Dy, Ho, Er and Tm, which have been analysed by neutron diffraction. Rare earth structure relevant features are summarized. All compounds, except those with Pr, order magnetically at low temperatures. Magnetic order is confined to the rare earths; Co and Ni sites remain non-magnetic. RCoC₂ become ferromagnets; RNiC₂ order antiferromagnetically in different spin configurations. The type of order and R dependent moment configurations are explained by RKKY exchange and additional crystal field interactions.     

Comparative study for mutual separation characteristics of binary mixed oxides Y2O3–Ln2O3 (Ln = Dy, Ho and Er) and Ho2O3–Er2O3 using stepwise chlorination–chemical vapor transport reaction mediated by vapor complexes KLnCl4

Mutual separation characteristics for binary oxide mixtures Y₂O₃–Dy₂O₃, Y₂O₃–Er₂O₃ and Ho₂O₃–Er₂O₃, in which these four kinds of rare earth ion(III) have very similar ion radius values, using a stepwise chlorination–chemical vapor transport (SC–CVT) reaction mediated by vapor complexes KLnCl₄ have been investigated in different temperature gradients. The unexpected results, together with that for Y₂O₃–Ho₂O₃ reported previously, are used to make a comparative analysis for the effect of ion radius values on the SC–CVT reaction for mutual separation of rare earths. Both the main deposition temperature region tendency and total transport amounts of chlorides for YCl₃ with respect to the ion radius of Y(III) were exceptional compared with those of LnCl₃ (Ln = Dy, Ho and Er), which were observed both in the degressive temperature gradient and the wave-type temperature gradient. The main deposition temperature of the chlorides produced from the oxide mixtures was in the order of DyCl₃ > YCl₃, HoCl₃ < YCl₃, ErCl₃ < YCl₃ and HoCl₃ > ErCl₃, total transported yields of the chlorides was in the order of DyCl₃ > YCl₃, HoCl₃ > YCl₃, ErCl₃ > YCl₃ and HoCl₃ > ErCl₃, and the largest separation factors 11.49 for Dy:Y, 15.28 for Ho:Y, 6.37 for Er:Y and 2.04 for Ho:Er in the lower temperature region were observed in the degressive temperature gradient, respectively. The results were discussed on the difference of ionic structure of Y on the one side and 4f lanthanoid elements of Dy, Ho and Er on the other hand, and verified that the ionic radius of the rare earth is one of the decisive factors of CVT reaction only for lanthanoid elements, not for Y. Furthermore, the improved separation factor values of 4.22 for Ho:Er and 3.20 for Er:Ho were obtained in the wave type temperature gradient due to variation of the dynamic conditions of CVT.     

Comparison of spectroscopic properties of nanoparticulate Lu2O3:Eu synthesized using different techniques

Two series of Lu₂O₃:Eu nanocrystalline phosphors were prepared using either combustion procedure with urea fuel or the Pechini procedure. The dopant concentration varied in both series from 0.2 to 13% with respect to Lu. Despite full crystallization and very similar microstructure of materials of both series, we found profound variations in their spectroscopic properties. The combustion-made phosphors were much less efficient emitters and their emission was strongly concentration-quenched above 3% of the dopant content. For the Pechini-derived materials, the concentration quenching was not observed below 10% of the dopant content and even for the dopant concentrations equal to 10 and 13% the quenching was insignificant. In EPR spectra for Gd³⁺-doped materials, a significant broadening of lines was found for the combustion-made powders. All these observations imply a strong agglomeration of the dopant ions in the specimens made by applying urea fuel in the combustion process. A semi-two-phase composition was suggested in the combustion-prepared powders. In the Pechini-derived nanocrystalline powders, the dopant ions are uniformly, statistically distributed in the host lattice.     

Optical study of praseodymium dicarboxylate [Pr(H2O)]2[O2C(CH2)3CO2]3.4H2O

Praseodymium dicarboxylate, [Pr(H₂O)]₂[O₂C(CH₂)₃CO₂]₃.4H₂O]–glutarate, Pr[glut], is synthesized by hydrothermal techniques. The title compound crystallizes in the monoclinic space group C2/c (No. 15). The rare earth cation is coordinated by nine oxygen atoms, eight oxygen atoms from the carboxylate groups and one from the water molecule. The local symmetry of Pr site is low, C_s. The absorption spectra of Pr[glut] are recorded from the visible to the far IR domain at 300, 77 and 9 K. Under various Ar⁺ laser excitations no emission is detected from ³P₀ and ¹D₂ excited levels of Pr³⁺ ion. In the low temperature absorption spectra only one electronic line is recorded for ³H₄→³P₀ transition. It confirms a unique local environment for the rare earth ion in Pr[glut]. The utility of the ‘barycenter curves’ in the attribution of electronic lines is demonstrated. Energy level scheme of 36 Stark components is deduced from the absorption spectra. The parametric calculation was performed on the whole 4f² (Pr³⁺) configuration with the starting set of crystal field parameters obtained previously for the Eu³⁺ ion in the isostructural compound. Eight free ion and nine phenomenological crystal field parameters in C_2v symmetry reproduce quite well several electronic levels of Pr³⁺ ion experimentally observed in Pr[glut]. A good r.m.s. standard deviation of 14.8 cm⁻¹ is obtained.