Search

Gallium nitride co-doped with magnesium and europium shows great potential for active layers in red light emitting diode structures due to strong and sharp luminescence emission around 620 nm. In this work, sharp and intense Eu3+ luminescence lines from the excited states of the 5D J (J = 0, 1) multiplets to the ground states of the 7F J (J = 0, 1, 2) multiplets have been analyzed using a C 2 v crystal-field equivalent operator Hamiltonian. A model of Eu centers with the C 2 v symmetry has been proposed to be an Eu3+ complex accompanied by either a pair of nitrogen and gallium vacancies (V N - V Ga) or a pair consisting of a nitrogen vacancy and magnesium impurity (V N - Mg Ga) in the vicinity of the Eu ion based on the crystal-field analysis, the selection rules and the observed polarization of the Eu3+ luminescence lines. Energy transfer from the host to the Eu ions under band-to-band excitation occurs through electron-hole recombination between V N with the electron-like state and V Ga or Mg Ga with the hole-like state; these may be associated with the shallow-trapped or deep-trapped states, respectively, proposed as the energy transfer mechanism in previous literature. • Polarized photoluminescence/cascade-luminescence from ex situ Eu-doped GaN(Mg). • Energy levels/states of 7F 0 ,7F 1 and 7F 2 multiplets of Eu3+ experimentally estimated. • Model of Eu centers in GaN(Mg) with C 2 v (orthorhombic) symmetry proposed. • Eu complex with N/Ga vacancy pair, or a pair consisting of N vacancy and Mg impurity. • Energy transfer GaN.→Eu via recombination between these electron-like/hole-like states [ABSTRACT FROM AUTHOR]

We present a modified version of the Judd-Ofelt theory, which describes the intensities of f-f transitions for trivalent lanthanide ions (Ln3+) in solids. In our model, the properties of the dopant are calculated with well-established atomic-structure techniques, while the influence of the crystal-field potential is described as a perturbation, by three adjustable parameters. Compared to our previous work (Hovhannesyan et al., 2022 [28]), the spin-orbit interaction within the first excited configuration 4f w − 1 5d is described in a perturbative way, whereas it is exactly taken into account in the ground configuration 4f w , using all the eigenvector components of the free-ion levels. Moreover, the wavelength-dependence of the refractive index of the host material is also accounted for. We test the validity of our model on three ions: Eu3+, Nd3+ and Er3+. The results of the extension are satisfactory, we are able to give a physical insight into all the transitions within the ground electronic configuration, and also to reproduce quantitatively experimental absorption oscillator strengths. We also performed calculations of standard JO parameters, and the results are in good agreement with the values reported in the literature. The code used to make the calculations is available on GitLab. • An extension of Judd-Ofelt theory is developed. • The model is based on accurately calculated free-ion properties. • Model is validated on trivalent Eu, Nd and Er. [ABSTRACT FROM AUTHOR]

Abstract We studied the effect of europium (Eu) doping on the near band edge emission of ZnO thin films, fabricated by sputtering and high temperatures annealing. The doping concentration of Eu in the ZnO films was varied from 0.01 to 0.62 at.%. Photoluminescence (PL) spectra showed that the films ultra-violet (UV) emission was enhanced very much by high temperature treatment and was stronger for the Eu doped ZnO than that for the un-doped ZnO films after 1100 °C annealing. X-ray diffraction showed the films had hexagonal wurtzite structure, the width of the ZnO (002) plane diffraction peak was sensitive to the anneal temperature and also to the Eu doping concentration, and Zn silicates had formed after the 1100 °C annealing. Scanning electron microscopy showed that the surface morphology of the films became more uneven with increasing Eu concentration. The PL decay spectra inferred that the lifetime of the UV PL was correlated with the size of ZnO nanocrystals in the films. The results support that the intensity of the UV PL is primarily influenced by the crystalline perfection of the films which is also influenced by the Eu doping concentration. [ABSTRACT FROM AUTHOR]

Abstract In this paper we will be presenting JOES (Judd-Ofelt from Emission Spectra), an application software for calculation of the Judd-Ofelt intensity parameters and derived quantities from the emission spectra of Eu3+ doped materials. The program is written to be user friendly and it requires no previous experience in the field of study. This Free and Open-Source program written in JAVA, works on Windows, Linux and MAC OS operating systems. Program has been tested on three europium doped oxides with good luminescent properties: TiO 2 :Eu3+, ZrO 2 :Eu3+ and Nb 2 O 5 :Eu3+. We wish to give to the researchers this theoretical tool which can make the calculations easier, faster and more reliable. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Europium-doped hydroxyapatite has attracted considerable scientific attention to smart drug delivery scaffold applications because of its biocompatible and traceable luminescence features. In this sense, to investigated the europium incorporation mechanism and photoluminescence properties in the presence of surfactant organic molecules the europium doped-hydroxyapatite samples were synthesized via co-precipitation with hexadecyl trimethylammonium bromide (CTAB) micelles mediated approach. Results of the X-ray absorption spectroscopy techniques (XANES and EXAFS) showed that Eu 3+ ions were incorporated preferentially at the Ca (1) site with local charge compensating via oxygen interstitial ion for samples calcined under air at 450 °C/4 h °C. Europium(III) luminescence analysis suggested that Ca site symmetry became distorted in CTAB medium. [ABSTRACT FROM AUTHOR]

Acetylacetonate (acac) passivated and europium incorporated ZnGa 2 O 4 nanocrystals (ZGO:Eu NCs) were successfully prepared via a facile one-step non-injection process in oleylamine at a relatively low reaction temperature of 300 °C under N 2 ambient. The resultant ZGO:Eu NCs exhibited a well-dispersed morphology with an average particle size of 4 nm. The enhanced and broad absorption band from 250 to 450 nm is attributed to the synergistic effect between the acac as an antenna and the coexistence of Eu 3+ and Eu 2+ . Under 405 nm excitation, a full spectrum emission covering from 400 to 720 nm was observed. The sharp red emission coming from Eu(III) 5 D 0 → 7 F J (J = 1–4) transitions can be enhanced by adjusting Eu concentrations and reaches the optimum at 20 at% Eu. Subsequently, the as-prepared NCs were transferred into an aqueous media via a ligand exchange by polyethyleneimine (PEI) to obtain the hydrophilic ZGO:Eu@PEI NCs. The initial fluorescent properties are preserved well. Finally, the strong red fluorescence emission, suitable excitation window, high photo-stability, excellent water solubility, and prominent bio-compatibility make ZGO:Eu@PEI NCs as high quality bio-imaging probes successfully identify living KB cells. The method mentioned in this paper overcomes the bottle-neck of the inorganic bulk phosphors as probes in bio-imaging, and as a result, expands their applications in optical detection and medical diagnosis fields. [ABSTRACT FROM AUTHOR]

This work focuses on Sr 2 CeO 4 materials containing Ag + and Eu 3+ that are obtained by a combustion method using citric acid as a precursor. The heat-treatment at 1100 °C was efficient and phase impurities are eliminated with presence of Ag + , favoring the Sr 2 CeO 4 formation, as confirmed by XRD. SEM analysis shows a proportional decrease in the organization of particles as a function of doping material, with a nanorods morphology. Diffuse reflectance shows that materials are transparent at visible region, with absorption at UV region. Exciting Sr 2 CeO 4 -based materials at 270 nm, photoluminescence analysis reveal a band at 470 nm, characteristic of this material and, incorporating Eu 3+ , emission bands beyond 470 nm are observed characteristic of Eu 3+ . Eu 3+ photoluminescence makes the Sr 2 CeO 4 materials present color coordinates at bluish green, green, white, yellowish pink and reddish orange regions of electromagnetic spectra. Decay lifetimes of Sr 2 CeO 4 and Eu 3+ were determined and are discussed. The results obtained demonstrate materials with a high potential for application in light emitting devices, and a methodology efficient at obtaining these materials. [ABSTRACT FROM AUTHOR]

Eu 2+ and Eu 3+ co-doped SrSO 4 microcrystals were synthesized by employing Eu 3+ as the sole doping source in the precipitation synthesis. As the annealing temperature increases from 200 to 1000 °C, it is found that the broad photoluminescence (PL) band of Eu 2+ peaking at 378 nm is dramatically enhanced in intensity as the cost of the narrowband emissions of Eu 3+ at 584, 591 and 612 nm, respectively. Moreover, Two broad PL bands, one of which is centered at 500 nm while the other is centered at 625 nm, are recorded upon post annealing. On the basis of density functional calculations, post annealing introduced oxygen vacancy is proposed to play critical roles in tuning the PL of Eu 2+ and Eu 3+ co-doped SrSO 4 . On one hand, the oxygen vacancy is responsible for the enhanced emission of Eu 2+ at 378 nm by reducing Eu 3+ to Eu 2+ . On the other hand, the oxygen vacancy acts as electron trap and luminescence center in SrSO 4 with the result of the broad PL band centered at 500 nm. Our results have demonstrated that the PL of Eu 2+ and Eu 3+ co-doped SrSO 4 microcrystals can be tuned by simply varying the post annealing temperature. [ABSTRACT FROM AUTHOR]

Very few devices are capable to measure temperature with high precision and sensitive, mainly in the micro and nanoscale. It is known that for biological applications it is required high sensitivity devices in a short temperature range (288–323 K). Recent reports are proposing the use of ratiometric thermometers based in the luminescence of trivalent lanthanide ions. In this paper, the ratiometric thermometer characteristic was investigated in an alumino-phosphate glass doped with Eu 2 O 3 . The studied temperature range was 288 – 333 K, and the material presents high sensitivity values (1.25–1.68% per K). The luminescence of Eu 3+ -doped alumino-phosphate glass does no present losses by energy transfer mechanism in this temperature range, making a quick predicable thermometric parameter by use of ratio between the integrated intensities of 5 D 0 → 7 F 2 and 5 D 0 → 7 F 0 transitions, respectively. Both excitation and emission are in wavelengths not strongly absorbed by living tissues, becoming promising material to applications in the laboratories scale, as the temperature measurements of cell cultures, and monitoring of tissues that does not require high penetration of excitation wavelengths. [ABSTRACT FROM AUTHOR]

The optical performance of europium (Eu) doped SiAlON thin films and its preparation by pulsed laser deposition are studied. The undoped SiAlON films show a high refractive index (2.34) close to that of silicon nitride. After doping with Eu the oxygen content increases in the films and leads to the formation of an oxynitride with a refractive index of 1.87 and excellent transparency in the visible-near infrared. Upon excitation at 355 nm the films show a broad band (FWHM of 200 nm) emission in the visible range (400–750 nm) that is associated to the emission of the Eu in the 2+ oxidation state. Enhancement of the emission together with a blue spectral shift has been found when the films are annealed at low temperature (600 °C). These films show promising properties for the development of Si compatible thin films integrated emitters. [ABSTRACT FROM AUTHOR]

In the present study, structural and photo-luminescence studies of Eu 3+ and Tb 3+ co-doped ZnMoO 4 host matrix has been investigated in detail. ZnMoO 4 :Eu 3+ /Tb 3+ have been synthesized via a simple and cost effective co-precipitation method. XRD, Raman and FTIR studies confirmed its triclinic structure of Eu 3+ /Tb 3+ co-doped ZnMoO 4 host. Emission spectra of the measured samples corroborate the dominant electric dipole transition emission ( 5 D 0 - 7 F 2 ) intensity over magnetic dipole transition emission ( 5 D 0 - 7 F 1 ) intensity. Moreover, the improvement in red emission ( 5 D 0 - 7 F 2 ) for Eu 3+ (3 at%) and Tb 3+ (2 at%) and high asymmetric ratio ∼10.4 is observed which dictates it as a highly red emitter. Additionally, commission international de-I′ Eclairage (CIE) values approaches to NSTC. Color purity of red emission improves after Tb 3+ co-doping. Photoluminescence studies reveals that Tb 3+ acts as a sensitizer for the Eu 3+ activated ZnMoO 4 host matrix. Study reveals that Eu 3+ /Tb 3+ co-doped ZnMoO 4 can be excited by near UV device, which is bottleneck in the advancement of LEDs technology. [ABSTRACT FROM AUTHOR]

Cubic Eu 3+ -doped Lu 2 O 3 nanocrystals were synthesized via combined Pechini-foaming method. Doping concentration effect on the structural and luminescence properties was studied. It was found that the increase of Eu 3+ concentration leads to the growth of unit cell parameters and red shift of Raman lines. The optimal doping concentration and shape of emission lines were studied upon different excitation mechanism. Radiative and nonradiative transition rates and Judd-Ofelt parameters were calculated using the model of 4f–4f intensity theory. The type of multipolar interaction resulting in luminescence concentration quenching was determined. [ABSTRACT FROM AUTHOR]

Controlling of valence states of metal ions doped in glasses has attracted considerable interest due to the possibility of looking toward optical applications. In this study, new Na 2 O-Al 2 O 3 -SiO 2 glasses were developed to dope Eu 2+ and Mn 2+ with well controlled valence states by heating in H 2 gas atmosphere, and the changes in the valence state of doped-ions and their fluorescence properties were investigated using visible and infrared optical absorption spectroscopies, X-ray absorption fine structure spectroscopy, and fluorescence spectroscopy. Among Eu 3+ , Mn 3+ and Mn 2+ ions incorporated in the as-prepared glasses, the Eu 3+ and Mn 3+ ions were reduced to Eu 2+ and Mn 2+ ions, respectively, by heating in H 2 gas and OH bonds were concurrently formed. The fluorescence spectra of glasses heated in H 2 exhibited broad emission bands at 450 and 630 nm wavelength, assigned to the Eu 2+ and Mn 2+ , respectively, ions, in which the fluorescence intensity at 450 nm was observed to decrease with increasing Mn 2+ ion content. The increased fluorescence intensities were analyzed as the energy transfer from Eu 2+ to Mn 2+ ions and the energy transfer efficiency was estimated with a concentration of Eu 2+ and Mn 2+ ions. [ABSTRACT FROM AUTHOR]

Up-converting properties of LiLaP 4 O 12 :1%Tm 3+ , 50%Yb 3+ , x% Eu 3+ nanocrystals were investigated upon 975 nm excitation. It was shown that their emission color can be tuned from blue to orange via changing Eu 3+ concentration from 10% to 49%. The potential suitability of these nano-phosphors for non-contact temperature sensing was investigated. Thermal changes of luminescence intensity ratio of 1 D 2 → 3 F 4 and 1 G 4 → 3 F 4 emission bands of Tm 3+ ions were strongly affected by Eu 3+ concentration owing to increasing efficiency of distance-dependent Tm 3+ →Eu 3+ energy transfer. The sensitivity of such luminescence thermometer was varying from 0.1%/°C to 1.9%/°C in response to varying Eu 3+ concentration from 49 down to 10%. [ABSTRACT FROM AUTHOR]

Novel Eu 3+ activated Gd 2 Mo 4 O 15 phosphors were synthesized at the comparatively low temperature of 700 °C via solid-state reaction. X-ray powder diffraction results demonstrate that the phosphors crystallize in the triclinic crystal structure, the space group P I ¯ . The photoluminescence spectra and ultraviolet-visible (UV–vis) reflectance and transmittance spectra indicate that Eu 3+ doped Gd 2 Mo 4 O 15 phosphors show a broad and strong absorption band covering ultraviolet (UV) and near ultraviolet (NUV) regions and the crystals emit red light with peak maximum at about 618 nm under excitation of UV, NUV or blue light. The optimal doping concentration of Eu 3+ ions in Gd 2 Mo 4 O 15 phosphors is around 50 mol% and the main concentration quenching mechanism is determined to be the exchange interaction. [ABSTRACT FROM AUTHOR]

We report on a detailed spectroscopic study of Eu 3+ ions in the monoclinic KYb(WO 4 ) 2 crystal. The polarized room and low-temperature absorption spectra are measured. The maximum σ abs corresponding to the 7 F 1 → 5 D 1 transition is 1.32×10 –20 cm 2 at 534.2 nm with a bandwidth of 0.7 nm (for E || N m ). The Stark sub-levels of the excited mulitplets are determined. A Judd-Ofelt analysis is applied to the Eu 3+ :KYb(WO 4 ) 2 crystal to determine the probability of spontaneous transitions, radiative lifetimes and luminescence branching ratios. Within the strong configuration interaction (SCI) approximation, the intensity parameters are Ω 2 =4.757, Ω 4 =2.295, Ω 6 =1.644 [10 –20 cm 2 ] and Δ f =50160 cm –1 . The radiative lifetime of the 5 D 0 state is 351 µs. The maximum stimulated-emission cross-section corresponding to the 7 F 1 → 5 D 1 transition is 1.44×10 –20 cm 2 at 703.2 nm (for E || N m ). Under UV excitation, the Eu 3+ :KYb(WO 4 ) 2 crystal provides intense red photoluminescence with CIE coordinates, x=0.675, y=0.325. [ABSTRACT FROM AUTHOR]

Eu 3+ doped Mg 2 Al 4 Si 5 O 18 phosphors were prepared by the solid-state reaction. The first principles calculation, XRD, diffuse reflection spectra, photoluminescence spectra and thermal quenching are carried out to investigate the electron structure, crystal structure, photoluminescence and thermal properties. The calculation results show that Mg 2 Al 4 Si 5 O 18 possesses the direct band gap of about 5.1 eV. With the introduction of Eu 3+ , the energy gap becomes obviously smaller due to the discontinuity of exchange-correlation energy. Between HOMOs and LOMOs, a series of f orbitals of Eu 3+ can be observed, which is the essential condition to realize the efficient 4 f –4 f transitions of Eu 3+ . The experimental results indicate that the samples can efficiently absorb the UV-light and emit the red light with the highest peak at 614 nm. With the co-doping of Bi 3+ as sensitizer, the emission intensity of Eu 3+ increases by about 49% due to the energy transfer between Bi 3+ and Eu 3+ . With the introduction of Li + /Na + /K + as charge compensators, the emission intensities of Mg 2 Al 4 Si 5 O 18 : Eu 3+ are enhanced by about 22%, 18% and 5%. With the temperature increase, the emission intensity of all samples, especially the Bi 3+ doped samples, dramatically declines, which reveals two important effects: one is that the Eu 3+ emission is very sensitive to temperature, and other is that the complex energy transfer process among the excited and ground states of Eu 3+ , Bi 3+ or host absorption occurs. To explain the degradation, the mechanism based on the configurational coordinate diagram is proposed and this model could be helpful for the understanding of the energy transfer mechanism among the various energy levels in the process of temperature change. [ABSTRACT FROM AUTHOR]

A series of Eu 3+ (1–7 mol %) doped Y 2 SiO 5 red nanophosphors were prepared by eco-friendly combustion route using Calotropis gigantea latex as a fuel. The obtained nanophosphors were calcined at 1000 °C and characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), Raman studies, UV–Visible and photoluminescence (PL) spectroscopic techniques. PXRD were used to determine the structure of the phosphors, showing that the product was monoclinic phase of X1 type Y 2 SiO 5 having a phase group P2 1/c n. 14. The PL properties of samples exhibited an intense broad red emission band upon excitation with 397 nm, with a peak at 612 nm, color coordinates of (0.5866, 0.4026), and average correlated color temperature ~2018.5 K. Based on Judd–Ofelt (J–O) theory, the intensity parameters ( Ω 2 and Ω 4 ) were evaluated from the emission spectra of Y 2 SiO 5 : Eu 3+ (1–7 mol %) nanophosphors. The registered trend ( Ω 2 < Ω 4 ) reveals the relatively high symmetry environment around the rare earth ion (RE) site in Y 2 SiO 5 as compared to other host matrix. The results show that prepared samples were compared with the commercially available compound and founds as par to the commercial compound hence it may be used as a potential red phosphors for near UV excited White LEDs applications. [ABSTRACT FROM AUTHOR]

Tb 3 + and Eu 3 + single- and double-doped barium borate glasses are analyzed for their temperature-dependent luminescence and energy transfer properties. The glasses are investigated in the temperature range from 15 K to 700 K. The Tb 3 + doped glass has a higher temperature stability than the Eu 3 + doped one. Increasing the temperature leads to an enhanced energy transfer from Tb 3 + to Eu 3 + in the double-doped glass. The energy transfer mechanism is investigated in detail. [ABSTRACT FROM AUTHOR]

Eu, RE 3+ (RE = Dy, Sm, Tb) co-doped SiO 2 –CaF 2 –Al 2 O 3 –CaO oxyfluoride glasses have been prepared by the melt quenching method. By heating the precursor glasses at 670 °C for 1 h, glass–ceramics containing CaF 2 nanocrystallites were obtained. DTA and XRD measurements were performed. Excitation spectra of the prepared samples as well as photoluminescence spectra at the excitation of 355 nm and 450 nm were measured, CIE colour coordinates and colour rendering indexes were found. In the glass–ceramics the presence of Eu 2+ ions was observed by a broad emission band in the 400–500 nm spectral range. The most promising doping combinations for white light luminophores within our research are europium–dysprosium and europium–terbium, which allow obtaining white light both in glasses and glass–ceramics under 355 nm excitation. Heat treatment of glasses can be considered as a tuning mechanism to obtain white light because of the heat treatment dependent Eu 2+ emission. [ABSTRACT FROM AUTHOR]

Europium-doped hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP) and biphasic phosphate nanopowders were synthesized by co-precipitation method and their crystal structures and fluorescence properties were investigated depending on the pH of the starting solution. In the range of pH 6–10, HA and β-TCP phases coexist. The β-TCP proportion increased as the pH of the solution decreased, while HA yields decreased. At pH below 6, monophasic β-TCP powder was obtained after thermal treatment. In particular, HA and β-TCP can be used as luminescent materials when activated by Eu 3+ ions in substitution of Ca 2+ ions. Herein, the Eu 3+ ions doped HA and β-TCP phase composition were analyzed in order to investigate the fluorescence emission of the HA, β-TCP and biphasic compounds. Eu-doped HA exhibited a red-orange emission at 575 nm with several minor peaks at 610–640 nm, while Eu-doped β-TCP had an unexpected strong red emission at 610–620 nm and a secondary band at 590–600 nm. In fact, the Eu:β-TCP integrated emission area is almost 20-fold higher than Eu:HA for the same europium ion concentration. These results demonstrate the potential of Eu:β-TCP as biomarker for medical applications, as drug release and targeting based on their luminescent properties. [ABSTRACT FROM AUTHOR]

Zn co-doped and undoped Y 2 O 3 -Eu red phosphor was prepared by citric acid gel method and it was investigated to know its cathodoluminesecent properties at low voltage excitation (<2 kVs). In this connection the cathodoluminescence (CL) spectra of Zn co-doped and undoped phosphors were taken and they showed various line emissions along with a sharp red emission at 611 nm, irrespective of Zn concentration, due to 5 D 0 – 7 F 2 transitions from Eu luminescent center. It was found that the incorporation of Zn could significantly enhance the CL emission intensity of Eu at about 33% when compared with Zn undoped phosphor. It was also found the Zn co-doping could not alter the crystal structure whereas it could change the morphology of the particles. The promising results revealed the possible application of this phosphor materials as red phosphor for field emission displays [FEDs]. [ABSTRACT FROM AUTHOR]

Eu 3+ doped ZrO 2 coatings were formed by plasma electrolytic oxidation of zirconium in electrolyte containing Eu 2 O 3 powder. The content of Eu in coatings increases with the time of PEO process. The coatings are crystallized and mostly composed of monoclinic ZrO 2 phase. Photoluminescence (PL) emission spectra of Eu 3+ doped ZrO 2 coatings feature two distinct regions. The first region is related to ZrO 2 PL band with a maximum positioned at about 490 nm, while the second region in the orange–red part of the spectrum shows sharp emission bands which are related to f – f transitions of Eu 3+ from excited level 5 D 0 to lower levels 7 F J ( J =0, 1, 2, 3, and 4). Excitation PL spectra of Eu 3+ doped ZrO 2 coatings monitored at 480 nm feature a broad PL band with spectral maximum at about 280 nm. In contrast, the excitation PL spectra monitored at the wavelength of the most intense peak in emission PL spectra can be divided into two regions: (a) the broad band region from 240 nm to 350 nm with a maximum at about 250 nm, which is associated with the electron transfer transition from 2p orbital of O 2− ions to 4f orbital of Eu 3+ ions and (b) the region in the range from 350 nm to 550 nm with the series of sharp peaks, which correspond to direct excitation of the Eu 3+ ground state 7 F 0 into higher levels of the 4f-manifold. [ABSTRACT FROM AUTHOR]

In the present work it has been demonstrated that Eu doped ZnO–SnO 2 nanocomposite shows enhanced photoluminescence in comparison to individual ZnO:Eu or SnO 2 :Eu. Luminescence studies have confirmed that Eu 3+ ions mainly occupy Sn 4+ sites in the SnO 2 part of the composite. Hetero-junction assisted energy transfer from ZnO to SnO 2 :Eu 3+ has been assigned as the reason for this relative improvement in luminescence behavior. Based on the X-ray diffraction nuclear magnetic resonance studies it is confirmed that at higher annealing temperature, Zn 2 SnO 4 phase forming at the interface of SnO 2 and ZnO prevents the energy transfer between ZnO and SnO 2 :Eu and thereby decreases photoluminescence intensity. Deterrent of ZnO and SnO 2 interaction via silica dispersion of nanocomposite resulted in deterioration of luminescence properties further reaffirms the role of ZnO:SnO 2 hetero-junction. [ABSTRACT FROM AUTHOR]

We have prepared high quality crystals of pure SrI 2 and Eu-doped SrI 2 by our original “Liquinert” process and investigated their luminescence properties. Under the excitation with the 193 nm light of an ArF excimer laser, which corresponds to the wavelength above the bandgap of SrI 2 bulk crystals, the pure and Eu doped SrI 2 crystals exhibit no luminescence band related to defects or impurities around 560 nm. This fact indicates that the crystals prepared by the “Liquinert” process contain lower defects and/or impurities. When the Eu-doped SrI 2 crystals are excited with the 325 nm light of a He–Cd laser, only the luminescence band due to the 5d→4f transition in the Eu 2+ ions is observed around 425 nm. The 425 nm band observed at a forward configuration exhibits the shift to the longer wavelength side and the decrease of the luminescence intensity with increasing Eu concentration. The Eu concentration dependences of the peak wavelength and luminescence intensity are simulated on the basis of a simple self-absorption model. [ABSTRACT FROM AUTHOR]

The Judd-Ofelt theory, which is the most thorough and insightful method to determine theoretically the luminescent properties of the trivalent rare earth dopants, is here tested on Eu3+-doped glasses in the P 2 O 5 – SrO – CaO – Na 2 O system to assess their usefulness as luminescent thermometers. It is demonstrated that the thermometric sensitivity (change of the emission lines ratio in response to change in temperature) can be estimated using the Judd-Ofelt theory and aligns well with the experimentally obtained values. It is shown here that the addition of B 2 O 3 or SiO 2 in a phosphate network increases the absolute sensitivity due to an increase in the phosphate network connectivity while having no significant impact on the site of Eu3+ ions. The applicability of the Judd-Ofelt theory for predicting the thermometric parameters of a glass luminescent material, without the time-consuming measurement of the glasses spectroscopic properties as a function of temperature, is clearly demonstrated and allows for further development of novel efficient luminescent thermal sensors with high sensitivity. [Display omitted] • The luminescent thermometer performance of Eu3+-doped glasses is predicted by Judd-Ofelt theory. • The structure connectivity of the studied glass is increased by the addition of 5% of SiO 2 or B 2 O 3 (for P 2 O 5). • The increase in structure connectivity enhances the absolute sensitivity of Eu3+ luminescent thermometer. • Refractive index is the most determining factor in the enhancement of the absolute sensitivity. [ABSTRACT FROM AUTHOR]

Low temperature site selective spectroscopy has been used to probe the distribution of the Eu3+ ion on sites available in the ordered and disordered pyrochlores, Mg 2 La 3 Sb 3 O 14 and Ca 2 La 3 Sb 3 O 14. While the Mg-pyrochlore shows the presence of a single site with inversion symmetry, the emission spectrum of the Ca-pyrochlore is indicative of the presence of several different non-centrosymmetric sites for the dopant ion. These observations are consistent with the structural model that was proposed earlier. The 5D 0 →7F 0 emission transition in the Ca-pyrochlore occurs at very high energy (17,550 cm−1) and under a very specific excitation wavelength. Possible explanation for this observation is provided. • Low temperature site selective luminescence spectra have been measured on Mg 2 La 3 Sb 3 O 14 and Ca 2 La 3 Sb 3 O 14 doped with Eu3+. • A sharp 5D 0.→7F 0 line has been observed for Ca 2 La 3 Sb 3 O 14 upon excitation at 457 nm, attributed to [Eu3+-O2-] entities. • This feature is one of the most energetic 5D 0.→7F 0 lines reported in the literature for Eu3+ in an oxide host. [ABSTRACT FROM AUTHOR]

Eu 2+ -doped Ba 3 MgSi 2 O 8 phosphor, prepared by high-temperature solid state reaction in a reducing atmosphere, shows a blue emission under ultraviolet light excitation. When this phosphor is exposed to Xe-lamp radiation, the colorless powder turns orange, and the emission color changes to purple. The Xe-lamp induced orange color is successfully bleached by heat treatment at 350 °C for 30 min. Then, the emission color also returned to the original blue. The observed photochromic behaviors can be explained by electron transition in Eu 2+ -associated F A centers. [ABSTRACT FROM AUTHOR]

The impurities and dopants' inappropriate valences may deteriorate the performance of luminescent materials, cause waste of the precious rare earth (R) material and thus incur financial losses. The usual methods to detect the valence of rare earths; XPS, Mössbauer and XANES spectroscopies, are not sensitive enough for low concentrations and the EPR methods are not very suitable for powders. In this work, the comparison between the theoretical and experimental temperature-dependent paramagnetic susceptibilities was used to obtain quantitatively the concentrations of the impurity valence in Eu 2 O 2 S and Tb 2 O 2 SO 4 , both containing nominally only R 3+ . Minute (ppm level) Eu 2+ impurities could be analyzed because of the huge difference in the paramagnetic susceptibility between Eu 2+ and Eu 3+ at low temperatures. However, temperatures below 50 K are then needed whilst the Tb IV impurity in a Tb 3+ matrix can be observed already at higher temperatures. The latter method based on comparing the slopes of the Tb 3+ /Tb IV paramagnetic susceptibility vs temperature curves for the Tb 3+ /Tb IV couple is less sensitive than for the Eu 2+ /Eu 3+ one. Finally, the host independent temperature evolution of the paramagnetic susceptibility was calculated for Gd 3+ (or Eu 2+ or Tb IV ) to yield a simple analytical expression to be used universally. [ABSTRACT FROM AUTHOR]

[RE(TMA)] anhydrous complexes (RE 3+ : Y, Gd and Lu) present high red emission intensity with a quantum efficiency (~45%) for the [Y(TMA):Eu 3+ ] complexes, due to the absence of non-radioactive decay pathways mediated by water molecules. The complexes were prepared in mild conditions. All the compounds are crystalline and thermostable up to 460 °C. Phosphorescence data of the complexes with Y, Gd and Lu show that the T 1 state of the TMA 3− anion has energy higher than the 5 D 0 emitting level of the Eu 3+ ion, indicating that the ligand can act as an intramolecular energy sensitizer. The photoluminescence properties of the doped materials were studied based on the excitation and emission spectra and luminescence decay curves. The experimental intensity parameters ( Ω λ ), lifetimes ( τ ), radiative ( A rad ) and non-radiative ( A nrad ) decay rates were determined and discussed. [ABSTRACT FROM AUTHOR]

Biocompatible nanoparticles possessing persistent luminescence properties offer attractive possibilities for in vivo imaging applications as it allows an excitation of the sensors outside the animal before injection and a long-lasting emission of light. Here we report the development of highly biocompatible calcium phosphate nanoparticles doped with europium, Mn 2+ and Ln 3+ (Ln 3+ =Dy 3+ , Pr 3+ ) ions synthesized by hydrothermal route and tailored to present red-near infrared persistent luminescence after UV excitation. Nanosize biphasic HAp/β-TCP compounds with sphere and rod-shaped were obtained. Two emission bands in the red-near infrared range were observed and attributed to 4 T 1 → 6 A 1 transitions of Mn 2+ ions in HAp/β-TCP. An annealing treatment in reductive atmosphere post-synthesis was essential to reveal persistent luminescence properties. Indeed, such thermal treatment allows reducing Eu 3+ ions in Eu 2+ ions and generating required defaults as oxygen vacancies in the crystal necessary for red emission in accordance with persistent luminescence mechanism. These nanoparticles have been tested for the first time for in vivo imaging on small animal as proof of concept of prospective highly biocompatible nanoprobes. [ABSTRACT FROM AUTHOR]

In the present work, we report on a systematic study on structural and spectroscopic properties Eu 3+ and Er 3+ -doped Nb 2 O 5 prepared by sol–gel method. The Eu 3+ ions were used as structural probe to determine the symmetry sites occupied by lanthanide ions. The Eu 3+ -doped Nb 2 O 5 nanocrystalline powders were annealed at different temperatures to verify how the different Nb 2 O 5 crystalline phases affect the structure and the luminescence properties. Er 3+ -doped Nb 2 O 5 was prepared showing an intense NIR luminescence, and, visible luminescence on the green and red, deriving from upconversion process. The synthetized materials can find widespread applicability in photonics as red luminophor for white LED (with tricolor), optical amplifiers and upconverter materials. [ABSTRACT FROM AUTHOR]

A new approach to calculate the effective Ln–Ln energy transfer rates in a doped crystal matrices was proposed and successfully applied to the YVO 4 :Yb 3+ ,Er 3+ upconversion system. This approach is based on the known set of Ln–Ln distances obtained from the crystal structure of the matrix and the probabilities of their occurrence. The non-radiative energy transfer rates were calculated in the intermediate coupling scheme taking into account the shielding of the 4f electrons. The required partial (that is, forced electric dipole-only, lacking the dynamic coupling contribution) Judd–Ofelt Ω λ parameters were calculated using the Simple Overlap Model (SOM). The spectral overlap factor F was estimated from optical absorption measurements. A simplified “one level-one manifold” energy level scheme was applied. The F 7 / 2 4 , H 11 / 2 2 and S 3 / 2 4 states of Er 3+ were treated as an effective level. The set of rate equations containing radiative, non-radiative and energy transfer processes was solved numerically using fourth-order Runge–Kutta method. Both continuous and pulsed excitation modes were simulated. The dependence of the upconversion intensity upon the pump power was found. The simulations resulted in good agreement with the experimental results and provided new insights into the dynamics of the upconversion process and a connection between the macroscopic properties and the microscopic description. [ABSTRACT FROM AUTHOR]

Eu 3+ doped GdAlO 3 powder synthesized by solid state reaction was investigated for аpplication in luminescence thermometry. Phase composition of material was confirmed by X-ray powder diffraction analysis. The photoluminescence emission spectra were collected under excitation of 399 nm, while elevating the temperature of the sample from the room temperature to 793 K. Emissions from 5 D 1 → 7 F 1 and 5 D 0 → 7 F 2 characteristic transitions of Eu 3+ ions are selected for the temperature-dependence study using the fluorescence intensity ratio method. Emission decay curves measured at the strongest emission peak centered at 614 nm were recorded in a same temperature range. Data analysis showed that thermometry by fluorescence intensity ratio method can be used over the temperature region 293–793 K with the maximal relative sensitivity of 2.96% K −1 (at 293 K). Temporal dependence of emission (lifetime) provides temperature sensing from 620 to 793 K with the maximal relative sensitivity of 2.28% K −1 . [ABSTRACT FROM AUTHOR]

Hybrid nanocomposites are multifunctional materials and their properties are the consequence of molecular interaction between inorganic and organic phases. These materials are interesting hosts for lanthanide ions, such as Eu 3+ . The purpose of this research was to synthesize Eu 3+ doped SiO 2 –PMMA hybrid nanocomposites by a sol–gel process and to study the effects of thermal treatment on the structure and luminescent properties of the material. Structural characterization was carried out using the FTIR, TG and 29 Si NMR techniques, however, the luminescence studies were more sensitive to detect the slight structural changes resulting from the thermal treatment. The Eu 3+ ions inserted into the matrix behaved as a structural probe and make it possible to notice the symmetry change from Eu 3+ site, the decrease in the number of hydroxyl coordinated groups and the improvement in quantum efficiency as a result of the thermal treatment. In addition, the Judd–Ofelt intensity parameters were obtained and supported the interaction between the rare earth and hybrid material. The hybrid was obtained as a stable material until 200 °C and the high sensitivity of the Eu 3+ ions in the system may be used in future applications as thermal sensors, for example. [ABSTRACT FROM AUTHOR]

We report the ab initio embedded cluster calculations of Eu 2+ -doped CaF 2 . The 4 f →5 d transition bands were identified based on the complete active space self-consistent field (CASSCF) and the second order perturbation theory (CASPT2) calculations for the energies of the Eu 2+ 4 f 7 and 4 f 6 5 d 1 states including the spin–orbit interactions. The active space was derived by distributing 13 electrons (7 open-shell α electrons plus 3 α and 3 β electrons) in 15 active molecular orbitals with Eu 4 f , 5 d , and 5 p as main characters. To improve the theoretical prediction of the absorption spectra, we added both the diffuse functions on F atoms and the basis functions on the second neighbor Ca atoms to the basis set used in our previous paper [J. Lumin. 145 (2014) 941]. As a result, the predicted 4 f →5 d ( t 2 g ) transition energy and intensity patterns improved slightly; they were also in better agreement with the experimental absorption spectra. [ABSTRACT FROM AUTHOR]

Lanthanum zirconate (La 2 Zr 2 O 7 =LZO) pyrochlores doped with varying concentrations of Eu were synthesized using a low temperature gel-combustion synthesis route and characterized using X-ray diffraction, scanning electron microscopic and photoluminescence techniques. The final annealing temperature of the system could be brought down to 700 °C to produce a single phase compound. In addition, the optimum activator ion concentration for maximum luminescence yield was evaluated for the system. The site occupancy for the Eu ions was also investigated which suggested that at 500 °C, the ions were on the surface of the LZO host and later diffused into the lattice and replaced the La 3+ ions on annealing at 700 °C 5 h. However, due to difference in the ionic radii, the doped RE ions were of the inversion center forming a D 2d symmetry around them. For the first time the radiative properties and the commercial utility of the LZO system have been investigated. These parameters were used to get an idea about the M–L bond covalency in the system. The radiative properties suggested the system can be used as a potential ‘red’ emitting phosphor. [ABSTRACT FROM AUTHOR]

The incorporation of Bi 3+ and Li + as co-dopants in Eu 3+ -doped aluminum oxide films deposited by the ultrasonic spray pyrolysis technique and its effect on the luminescence characteristics of this material are described. Both Bi 3+ and Li + do not introduce new luminescence features but affect the luminescence intensity of the Eu 3+ related emission spectra as well as the excitation spectra. The introduction of Bi 3+ generates localized states in the aluminum oxide host that result in a quenching of the luminescence intensity, while Li + and Bi 3+ co-doping increase the luminescence intensity of these films. [ABSTRACT FROM AUTHOR]

Erbium (Er 3+ ) doped ytterbium garnet Yb 3 Al 5− y Ga y O 12 ( y =0, 0.55 and 1.1, YbAGG) thick films were grown by the isothermal liquid phase epitaxy method (LPE) on LuAG or YAG substrates. The influence of gallium on the photoluminescent properties of Er 3+ is presented in this paper. Room temperature transmission and emission spectra were measured for the 0.5 at% Er 3+ :YbAGG films with a different doping level of Ga. Also Er 3+ :Yb 3 Al 3.9 Ga 1.1 O 12 ( y =1.1) films with a different doping level of erbium (0.5, 1 and 2 at%) were tested. The presence of gallium significantly affects the fine splitting and total intensity of erbium emission in an infrared region (the transition 4 I 13/2 → 4 I 15/2 ). Even at the highest doping level of erbium (2 at%), no up-conversion luminescence was observed, resulting in a maximum efficiency of the infrared emission. The lifetime of luminescence at 1530 nm was studied for all samples. [ABSTRACT FROM AUTHOR]

A series of Er 3+ ions doped tellurium calcium zinc niobium borate glasses were prepared by the melt quenching technique. The prepared samples were investigated by optical absorption and near infrared fluorescence spectroscopic studies. The obtained Judd–Ofelt intensity parameters Ω λ ( λ =2, 4 and 6) were determined through experimental and calculated oscillator strengths obtained from absorption spectra and their results are studied and compared with reported literature. The stark-level energies of 4 I 13/2 excited and 4 I 15/2 ground states were evaluated by using both the absorption and emission measurements. The effect of Er 3+ ion concentration on the emission intensity of 4 I 13/2 → 4 I 15/2 transition was discussed. Intense and broad 1.53 µm infrared fluorescence is observed at 980 nm diode laser excitation. Photoluminescence (PL) and its decay behavior studies were carried out for the transition 4 I 13/2 → 4 I 15/2 at 1.53 µm emission. The broad emission together with higher values of the bandwidth (81 nm), stimulated emission cross-section (32.25×10 −22 cm 2 ) and lifetime (530 µs for 1.0 mol% of Er 3+ ) of level 4 I 13/2 make these glasses attractive for broadband amplifiers. From the analysis of spectroscopic data, the present glass is a prospective photonic material for practical applications in the visible and NIR region. [ABSTRACT FROM AUTHOR]

Trivalent dysprosium doped strontium aluminate (SrA1 2 O 4 :Dy 3+ ) was synthesized via the sol–gel combustion method to realize green afterglow in the absence of Eu 2+ luminescent centers. The morphology, crystal structure, photoluminescence and long afterglow of the SrAl 2 O 4 :Dy 3+ were characterized with scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and photoluminescence spectroscopy, respectively. The bluish-green photoluminescence of SrAl 2 O 4 :Dy 3+ consists of a broad emission band centered at about 520 nm and two characteristic emissions of Dy 3+ ions centered at 480 and 575 nm, respectively. The green afterglow of SrAl 2 O 4 :Dy 3+ is a broad emission band centered at around 520 nm, and the lifetime extracted from afterglow decay is found to be 53 s. The mechanism on the green afterglow from SrAl 2 O 4 :Dy 3+ is discussed in terms of the possible defect levels in the host. [ABSTRACT FROM AUTHOR]

Europium doped silicate Sr 2 Y 8 (SiO 4 ) 6 O 2 :Eu was successfully obtained by the reaction of nanocrystalline SrO/Y 2 O 3 :Eu 3+ and colloidal SiO 2 at 1000 °C in the reducing atmosphere (25%H 2 /75%N 2 ). It has typical apatite crystal structure with the P63/m space group. The distributions of Eu 3+ and Eu 2+ between the two crystallographic sites 4f and 6h in the apatite structure were investigated by means of photoluminescence techniques. Results show that both ions are present in 4f and 6h sites at initial Eu 3+ concentration of 0.1 mol%. With increasing concentration the occupancy of 4f sites by both ions increase faster. Due to significantly shifted luminescence of Eu 2+ ions from both sites a tunable broad band emission in the spectral range of 450–650 nm can be produced varying the excitation energy. With the excitation in the wavelength range of 380–400 nm, the resultant yellow emission has spectral distribution beneficial for high color rendering index (CRI). These phosphors are efficiently excited in the wavelength range of 300–500 nm, which can be executed by a near UV- or blue-emitting InGaN chip. While the emission intensity is quite stable up to 100 °C, the emission quantum efficiency (QE) of 45% is still below the value of commercial phosphors. [ABSTRACT FROM AUTHOR]

We investigated the Li + ion incorporation in Ba 2 GdNbO 6 :Eu 3+ perovskite by atomistic simulations based on energy minimization. We predicted the most probable sites occupied by Eu 3+ and Li + ions and the related charge-compensation mechanisms involved into these substitutions. The results show that the Eu 3+ and Li + ions are incorporated mainly at the Gd 3+ site. In the Li + ion case, there is a charge compensation by Nb Gd • • antisite. The crystal field parameters and the transition levels for the Eu 3+ ion in the BGN:Eu 3+ were calculated with basis on the simulated local symmetry of the Eu 3+ site. The results show that the mechanism of luminescent properties enhancement is the symmetry distortion induced by the Li + co-doping. [ABSTRACT FROM AUTHOR]

New fluoroaluminate–tellurite glasses with high thermal stability were fabricated through introducing TeO 2 into the fluoroaluminate glass (AlF 3 –YF 3 –CaF 2 –BaF 2 –SrF 2 –MgF 2 ). 2.7 μm emission properties were investigated through the measured absorption and emission spectra. For the first time it was found that the OH − absorption coefficient at 2.84 μm was reduced to 1/15 for the fluoride system by introducing TeO 2 . X-ray diffraction showed that the sample without TeO 2 composition showed some crystallization phases when the glass was reheated. However, the addition of TeO 2 changed the crystallization mechanism and improved the glass forming ability of the fluoroaluminate glass. Enhanced 2.7 μm emission was observed in the fluoroaluminate–tellurite glass under 980 nm excitation and the calculated spontaneous transition probability ( А ), branching ratio ( β ) and emission cross section ( σ em ) were larger than some reported values. These results indicate that this kind of fluoroaluminate–tellurite glass has potential applications as host material for 2.7 μm lasers. [ABSTRACT FROM AUTHOR]

Eu 3+ and Gd 3+ ions co-doped amorphous silica nanorods were prepared using a simple sol–gel method, and their luminescent properties were studied under the excitation of ultraviolet light. X-ray diffraction (XRD), Energy-dispersive X-ray (EDX) spectroscopy, Fourier transform infrared spectrum (FT-IR), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), and Photoluminescence (PL) spectra were employed to characterize the products in detail. The nanorods are uniform and their diameters and lengths are in the range of 200–300 nm and 500–700 nm, respectively. Energy transfer process in Gd 3+ and Eu 3+ co-doped silica, where a ground state of Gd 3+ , 8 S 7/2 , was selectively excited to a 6 I J state under the excitation of 274 nm, was studied in terms of luminescence spectra, which indict that the energy transfer of Gd 3+ –Eu 3+ is efficient. The mechanism of energy transfer from Gd 3+ to Eu 3+ is a resonant transfer, in which electric dipole–dipole interaction plays a leading role. Furthermore, the doping concentration-dependence of Eu 3+ ions on the energy transfer efficiency was also investigated. [ABSTRACT FROM AUTHOR]

Erbium (Er) doped zinc oxide (ZnO) sol–gel thin films were deposited on glass substrate using the spin coating method. The effect of erbium concentration and annealing temperature on structural and optical properties was studied. The annealed film was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectrum (EDX), micro-Raman, photoluminescence (PL) and UV–vis spectroscopy. All the films showed a wurtzite structure of polycrystalline nature with an average crystal size of 27.44 nm at 500 °C and 29.28 nm at 600 °C. The Raman spectra confirmed the absence of secondary phases in the Er doped ZnO films and the longitudinal optical phonon mode was upto the fifth order. Densely packed surfaces of the films were observed from SEM images. The presence and distribution of Zn, O and Er elements in the deposited films were confirmed by EDX analysis. The calculated value of exciton binding energy of ZnO film was 60 meV with a maximum value of 72 meV being observed for Er doped films. The near infra-red emission peak was observed at 1.63 eV through PL spectra studies. The average transmission was 80% with the calculated value of optical band gap being 3.26–3.32 eV. An increase in the refractive index value predicts the substitutional incorporation of Er ions in ZnO with the maximum optical conductivity being observed in the UV region. [ABSTRACT FROM AUTHOR]

Eu 3+ -doped YVO 4 nanopowders were prepared by the modified Pechini method. The structural properties were studied with XRD, SEM and Raman spectroscopy. XRD pattern indicates that nanocrystalline YVO 4 :Eu 3+ powders form only pure tetragonal phase. SEM images show that synthesized samples are mixture of large, well-faceted particles and weakly agglomerated nanoparticles. The symmetry of luminescent centers local surrounding was discussed in terms of asymmetry coefficient. Dependence of luminescent intensity on Eu 3+ doping concentration was studied at different excitation wavelengths. Lifetimes of 5 D 0 level were measured for all the synthesized nanopowders. Also the probabilities of radiative, nonradiative processes, and the radiative lifetimes were calculated. [ABSTRACT FROM AUTHOR]

Sr 3− x Eu x MoO 6 and Sr 2.7 Eu 0.3 Mo 1− y W y O 6 red phosphors were successfully synthesized by solid-state reaction method at 1260 °C for 6 h. The photoluminescence (PL) properties of Eu 3+ in this phosphor material were investigated by analyzing the excitation and emission spectra and the effect of Eu 3+ concentration. X-ray diffraction (XRD) patterns indicate the formation of Sr 3 MoO 6 :Eu 3+ pure phase. The excitation and emission spectra demonstrate that 30 mol% Eu 3+ :Sr 3 MoO 6 shows a broad charge-transfer (CT) band at around 365 nm and an intense red emission (616 nm, 5 D 0 → 7 F 2 transition), with Commission Internationale de I׳Eclairage (CIE) chromaticity coordinates (0.619, 0.376). The substitution of Mo 6+ with W 6+ results in a considerable enhancement of luminescence intensity and improved red color purity. All the results imply that the studied phosphors may be a promising red component for the application in the white light emitting diodes. [ABSTRACT FROM AUTHOR]

Eu 3+ -doped perovskite type CaZrO 3 -based phosphors were synthesized by the solid state reaction at 1400 °C for 6 h in air. To change the short range structure around Eu 3+ in the CaZrO 3 -based compounds, two different cations were selected and co-doped; Sr 2+ with a larger ionic radius compared with Ca 2+ in the CaZrO 3 , and Mg 2+ having a smaller one. According to the results obtained by our previous study, the chemical composition of the starting powder mixtures was controlled by taking into account of the dominant Eu 3+ substitution site as A-site (Ca 2+ ) for Ca 1− x Sr x −0.05 ZrO 3 :Eu 3+ 0.05 ( x =0.2, 0.4), and that as B-site (Zr 4+ ) for Ca 1− y Mg y Zr 0.95 O 3 :Eu 3+ 0.05 ( y =0, 0.02, 0.04, 0.06, 0.08, 0.1). The results of the X-ray diffraction analysis revealed that Sr 2+ mainly occupied the A-site as designed, and the lattice constants of the Ca 1− x Sr x −0.05 ZrO 3 :Eu 3+ 0.05 increased with increasing amount of the Sr 2+ -doping up to 35 mol% without secondary phase formation. Mg 2+ substitution to Ca 2+ at the A-site in the CaZr 0.95 O 3 :Eu 3+ 0.05 could be also achieved. However, the maximum amount of Mg 2+ in the CaZr 0.95 O 3 :Eu 3+ 0.05 was found to be low, approximately 6 mol%. CaZr 0.95 O 3 :Eu 3+ 0.05 showed characteristic emission of the Eu 3+ (f–f transition) by CTB excitation. The intensity of the dominant PL emission peak centered at 614 nm ( 5 D 0 - 7 F 2 ) increased consistently with the amount of the Mg 2+ -doping, and the 6 mol% Mg 2+ -doped sample exhibited the highest emission peak intensity which was approximately 1.4 times higher than that of the Mg 2+ -free CaZr 0.95 O 3 :Eu 3+ 0.05 . On the other hand, the emission peak intensity at 614 nm decreased with increasing amount of the Sr 2+ -doping. The relationships between the PL emission properties and the material parameters such as lattice constants of the host CaZrO 3 -based compounds, dominant Eu 3+ substitution site and the site symmetry around Eu 3+ in the host lattice were discussed from a viewpoint to improve the PL red emission properties of the Eu 3+ -doped CaZrO 3 -based compounds. [ABSTRACT FROM AUTHOR]

Europium-doped yttrium oxide thin films have been deposited by a spray pyrolysis method. The crystallite sizes are calculated to be ~50 nm using Scherrer׳s formula. Fourier transformed infrared spectroscopy (FTIR) reveals broad absorption with peak at 875 cm −1 . Surface morphology and elemental composition of the thin films are studied by a field-emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS). The energy gap ( E g ) of the thin film sample is found to be ~5.37 eV. The film exhibits photoluminescence (PL) emission over 525–550 nm, 585–601 nm, 612 nm and 620–632 nm under the excitation of 240 nm. Gamma (γ)-irradiated films exhibit two well-resolved thermoluminescent (TL) glows with peaks at 460 and 570 K. The TL glow curves are analyzed by a glow curve shape method. The activation energy and the frequency factor are found to be, respectively, ~0.6 eV, ~3×10 6 s −1 for 460 K and ~0.53 eV, ~46.72×10 3 s −1 for 570 K. [ABSTRACT FROM AUTHOR]