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Tb[sup 3+]-doped Lu[sub 2]O[sub 3] sintered ceramics were prepared in vacuum and in air. It was shown that the vacuum-sintered disks are able to store energy when irradiated with 300-nm or shorter photons. A small part of the stored energy could be recovered with 980-nm light. A much more significant amount of the stored energy could be released with red 647-nm photons. However, recovering the total stored energy could be accomplished only upon heating up to about 300 °C. Changes in absorption of the raw materials upon ultraviolet irradiation and subsequent IR (980 and 647 nm) treatments or upon heating at 300 °C are presented and discussed. A model for energy storing and recovering through the various IR irradiations or through heating is presented. At least two distinct ways of hole trapping as Tb[sup 4+] or V[sub k]-center as well as creation off and F[sup +] is suggested. [ABSTRACT FROM AUTHOR]

In the present work, bismuth-doped CaAl 4 O 7 phosphor powders were obtained via modified Pechini citrate process and their photoluminescence, radioluminescence and thermally stimulated luminescence properties were studied down to 20 K. At room temperature excitation in UV led to broad-band 3P 0,1 → 1S 0 Bi3+ luminescence with three maxima located in blue-green part of spectrum as well as Bi2+ emission around 760 nm assigned to the 2P 3/2 → 2P 1/2 transition. At 150 K an additional Bi3+ emission band peaking at 370 nm appeared and its intensity increased significantly upon further cooling. The presence of a few luminescent centers of Bi3+ in CaAl 4 O 7 was assigned to the presence of defects disturbing the local symmetry of activator ions. The radioluminescence spectra showed only two bands, an intense one at 760 nm clearly related to Bi2+ and a very weak component at 555 nm associated with one of the Bi3+ sites. These two emissions were also observed in the thermoluminescence of the material following its exposure to X-rays. The Bi3+ luminescence is suitably positioned to contribute the cyan color to white-LEDs. Its quantum yield is satisfactory, close to 40%. The Bi2+ 720–850 nm emission is attractive for bioimaging as it appears in the Ist biological window. • A novel bismuth-doped CaAl 4 O 7 phosphor materials have been developed. • The phosphor exhibits a complex emission originating from both Bi3+ and Bi2+ ions. • Multicomponent broad-band emission in UV–Vis arises from a few Bi3+ centers. • Bi2+ luminescence appears in the Ist biological window. • Bi2+ emission is predominant in radioluminescence and TL spectra [ABSTRACT FROM AUTHOR]

A comparative study of the luminescent properties of singly Sm 3+ -doped and Sm 3+ ,Na + co-doped strontium aluminates: Sr 1−x Sm x Al 4 O 7 and Sr 1–2x Sm x Na x Al 4 O 7 (x = 0.001–0.1), as a function of activator concentration at room and low (77 K, 16 K) temperature is reported. Upon an excitation at 402 nm all samples exhibit intensive orange-red emission due to the characteristic 4f-4f Sm 3+ transitions with maximum located at around 598.7 nm. It was found that luminescence properties of both series of materials differ significantly. In SrAl 4 O 7 :Sm 3+ at least four distinct activator symmetry sites were identified, which is due to presence of charge compensating defects in the crystal lattice and tendency to form Sm pairs. Charge compensation through alkali metal co-doping led to a smaller perturbation of the local environment symmetry of Sm 3+ ions and significantly enhanced luminescence intensity. In SrAl 4 O 7 :Sm 3+ ,Na + only two of the four non-equivalent centers of Sm 3+ were found. One of them corresponds to isolated Sm 3+ ion occupying basically undistorted Sr 2+ symmetry site offered by host lattice but the other is associated with Sm 3+ ions forming pairs. Analysis of the luminescence decay traces of both types of materials showed a decreasing decay time constant with rising activator concentration what was mainly attributed to cross-relaxation processes between Sm 3+ ions. This effect was slightly more pronounced for the Sm 3+ ,Na + co-doped series due to higher population of Sm 3+ pairs. Fitting of the 4 G 5/2 state fluorescence decay to the Inokuti–Hirayama model indicated different dominant mechanisms of the self-quenching luminescence of Sm 3+ in SrAl 4 O 7 :Sm 3+ and SrAl 4 O 7 :Sm 3+ ,Na + , respectively, dipole-quadrupole interaction and dipole–dipole interaction. [ABSTRACT FROM AUTHOR]

Ce 3+ doped and Ce 3+ ,Mn 2+ co-doped calcium aluminoborate (CAB) phosphors were synthesised by solid-state reaction method and their optical properties were studied. X-ray powder diffraction, SEM and TEM studies indicated the crystallization of the main trigonal CaAl 2 B 2 O 7 phase and the presence of an additional non-crystalline phase. It was also observed that increasing dopant concentration promotes phase separation. Hence, both series of phosphors demonstrated the changes in luminescence properties via activator concentration variation. Upon UV excitation (λ ex = 310 nm) Ce 3+ doped and Ce 3+ ,Mn 2+ co-doped materials yielded intensive blue and pinkish luminescence, respectively. The spectra of CAB:Ce 3+ samples showed a broad emission band due to 5d→4f transition of Ce 3+ , which broadened and shifted to longer wavelengths with increasing dopant content. Mn 2+ co-doping caused appearance of another broad-band emission with a maximum of 680 nm, resulting from the 4 T 1 ( 4 G) → 6 A 1 ( 6 S) transition of Mn 2+ . Detailed analysis of the emission and excitation spectra as well as decay time traces as a function of dopant concentration showed that efficient resonant energy transfer mainly occurs between Ce 3+ and Mn 2+ incorporated in the non-crystalline phase in CAB material. The estimated values of energy transfer efficiency of CAB:Ce 3+ (3%),Mn 2+ (4%) is close to 52%. [ABSTRACT FROM AUTHOR]

In the present work, yttrium aluminum garnet Y 3 Al 5 O 12−x N 2x/x (YAGN) was obtained using aluminum nitride (AlN) as a source of aluminum. YAGN was doped with the Ce 3+ ions (YAGN:Ce) in concentrations from 0.5 to 14 mol%. According to XRD analysis, the crystal structure of YAG is maintained with traces of Al 2 O 3 . Scanning electron microscope (SEM) studies showed that the nitrogen atoms are not quite uniformly incorporated into grains, which may easily lead to the formation of a number of various Y 3+ sites. This means that Ce 3+ ions can also occupy sites of different nitrogen/oxygen ratios. The probability of Ce 3+ entering different sites changes with the dopant concentration. The emission and excitation spectra of Ce 3+ exhibit concentration dependence. For concentrations in the range 0.5–7% emission bands are extended to longer and shorter wavelengths in comparison to the typical emission of Ce 3+ in YAG. With the increase in the concentration of active ions (10–14 mol%) excitation bands show further widening, and the emission bands shift gradually toward longer wavelengths, reaching the value of 45 nm for 14 mol%. The usefulness of these phosphors for application in white LED technology is discussed on the basis of the quantum efficiency of the emissions, luminescence decay times, and thermal quenching of the Ce 3+ emission. [ABSTRACT FROM AUTHOR]

Abstract: Results of structural and spectroscopic measurements of Sm3+ doped calcium aluminates: Ca1−x Sm x Al4O7 and Ca1−2x Sm x Na x Al4O7 (x=0.0005, 0.002, 0.01, 0.02, 0.03, 0.05) obtained by the modified Pechini method are presented. All samples yield intense orange–red emission under violet excitation (404.5nm). Narrow bands corresponding to characteristic f–f intraconfigurational transition of Sm3+ in excitation and emission spectra were observed. The influences of the concentration of Sm3+ as well as charge compensation by co-doping with Na+ ions on the luminescent properties of the phosphor were investigated. Detailed analysis of the emission spectra of Sm3+ doped and Sm3+,Na+ co-doped CaAl4O7 powders proved that activator ions substitute Ca2+ in the host. Co-doping with Na+ ions enhanced greatly the intensity of the luminescence. Concentration dependencies of the intensity of luminescence and its decay kinetics proved the emission quenching at higher dopant contents due to cross-relaxation processes between Sm3+ ions. Fitting of the 4G5/2 state fluorescence decay to the Inokuti–Hirayama model indicated dipole–dipole interaction as the dominant mechanism of the cross-relaxation processes. [Copyright &y& Elsevier]

Scintillator materials are widely used in X-ray medical imaging detector applications, coupled with available photoreceptors like radiographic film or photoreceptors suitable for digital imaging like a-Si, charge-coupled devises (CCD), complementary metal-oxide-semiconductors (CMOS) and GaAs). In addition, scintillators can be utilized in non-medical imaging detectors such as industrial detectors for non-destructive testing (NDT) and detectors used for security purposes (i.e. airport luggage control). Image quality and dose burden in the above applications is associated with the amount of optical photons escaping the scintillator as well as the amount of optical photons captured by the photoreceptor. The former is characterized by the scintillator efficiency and the latter by the spectral matching between the emission spectrum of the scintillator and the spectral response of the photoreceptor. Recently, a scintillator material, europium-activated lutetium oxide (LuO:Eu), has shown improved scintillating properties. LuO:Eu samples of compact nanocrystalline non-agglomerated powder were developed in our laboratory using homogeneous precipitation from a water-toluene solution in the presence of polyvinyl alcohol as a surfactant. In order to test their light-emission properties, experimental measurements under the excitation of X-ray spectra with X-ray tube voltages between 50 kVp and 140 kVp were performed. This range of applied voltages is appropriate for X-ray radiology, NDT and security applications. LuO:Eu was evaluated with respect to output yield and spectral compatibility of digital imaging photoreceptors (CCD-based, CMOS-based, amorphous silicon a:Si flat panels, ES20 and GaAs). High light yield and spectral compatibility increase the performance of the medical detector and reduce the dose burden to the personnel involved. In addition a theoretical model was used to determine the values for the LuO:Eu optical photon light propagation parameters. The inverse diffusion length was found to be equal to 33 cm/g. In addition LuO:Eu was found to match well with several photoreceptors capable of digital imaging (i.e. GaAs). [ABSTRACT FROM AUTHOR]

Abstract: HfO2 and HfO2:Eu powders were synthesized with Pechini method at temperatures in the range of 600–1500°C. Structural, radioluminescence and photoluminescence properties of the powders were investigated. The highest light output of about 20% of the efficiency of commercial GOS:Eu was found for materials containing 0.5% of Eu and prepared at 1500°C. The data shows, that further improvement of light output could be obtained if materials are processed at yet higher temperatures. Emission spectra indicate that Eu3+ experiences variety of symmetries of its surroundings. Undoped materials produce broad band emission peaking at 480nm and showing a significant afterglow. [Copyright &y& Elsevier]

Abstract: Molten salt synthesis procedure, homogeneous precipitation with urea and -flux aided routes are presented as interesting fabrication methods for making oxide luminescent materials. The properties of the powders made using these techniques are presented and analyzed. Emphasis is put on spectroscopic characterization of the products. [Copyright &y& Elsevier]

Abstract: Nanocrystalline Lu2O3 doped with 1at.% of Eu was obtained precipitating hydroxide of lutetium with urea at 80°C from water solution and decomposing the hydroxide to oxide at 500°C. Polyvinyl alcohol was used to hinder the particles growth during precipitation. The average size of the fabricated particles was 2–5nm. Although at 500°C the hydroxide decomposed to Eu-doped Lu2O3 traces of OH impurities were present in the material unless heated at 1200°C. Radioluminescence was very poor for samples heated at 800°C or lower temperature. After heating the precipitated powder at or above 1200°C the efficiency jumped 45 times reaching 75% of the output from commercial microcrystalline Gd2O2S:Eu. The properties make nanocrystalline Lu2O3:Eu prepared in the described way a promising X-ray phosphor for planar digital medical imaging. [Copyright &y& Elsevier]

The paper reports on the course of decomposition of hydrated lutetium nitrate and lutetium chloride to Lu2O3 in the eutectic mixture of NaNO2 and KNO2. It was shown that a crystallographically pure phase of the cubic Lu2O3 is formed at temperature as low as 250 °C. IR spectra revealed that the recovered powder contains some OH-contamination, however. The powders are characterized by crystallites sizes in the range of 18–30 nm in average. Emission and excitation spectra of Eu-doped powders show characteristic features for Eu3+ ion in an oxide host, which indicates that the procedure is appropriate for making activated nanoparticulate oxide phosphors. Most profound emission appears around 611 nm and the luminescence from the powder made starting with Lu(NO3)3 was noticeably higher compared to the product obtained from LuCl3. The excitation spectrum of Eu3+ emission at 611 nm contains a band related to the fundamental absorption of the lutetia host lattice, which indicates an existence of the host-to-activator energy transfer. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Nanoparticulate powders of Eu-doped Lu2O3 were prepared using combustion process and glycine as a fuel. Such powders could be relatively easily sintered to translucent bodies at 1700 °C. Excitation and emission spectra were recorded for both types of the materials. The excitation spectra revealed the existence of much more efficient energy transfer from the host to the dopant in the sintered ceramics. Strong variations in the relative intensities of the excitation transitions are seen when comparing the powder and its sintered analog. This was explained assuming preferential occupation of the C3i site in the glycine-derived powder in comparison with the pellets. Most profound emission under X-ray excitation was found for the sintered ceramic doped with 5% of Eu. [Copyright &y& Elsevier]

Lu2O3 doped with Eu of varying concentrations was prepared using a convenient combustion technique. Emissions from two different crystallographic sites, C2 and S6, were found and analyzed. Using various spectroscopic techniques, luminescence of Eu3+ exclusively from site C2 or site S6 could be detected. Kinetics of both emissions was characterized and time constants of 1.5 and 4.3 ms were found, respectively. Energy transfer from Eu3+ in site S6 to Eu3+ in site C2 was proved to take place when the dopant content reaches about 1% or higher. For rising activator concentration the transfer becomes more efficient and for heavily doped samples the emission from S6 site lasts in a vestige form only. The only emission transitions detected from Eu in centrosymmetric site S6 were the 5D0–7F1 three-line band. [Copyright &y& Elsevier]

Abstract: La2Hf2O7 nanopowders doped with different Pr concentrations (0.05–10mol.%) were synthesized by the Pechini method. XRD measurements confirmed the single crystalline phase formed already at 800°C and the structure was cubic pyrochlore. Luminescence excitation and emission as well as radioluminescence spectra were recorded for the materials. Both optical and X-ray excitation of La2Hf2O7:Pr produced a red emission resulting from the 4f–4f transitions of Pr3+ ions. Luminescence of materials synthesized at low temperatures was characterized by broadband glass-type emissions, while heat treatment at 1400°C led to spectra showing the typical for crystalline hosts narrow and intense 4f–4f transitions of Pr3+. [Copyright &y& Elsevier]

The study concerned with the current work is to provide a comparative investigation of the detective quantum efficiency (DQE) of Lu2O3:Eu phosphor screens, prepared with different grain shape/size grains, specifically spherical grains, with sizes 50 nm, 200 nm, and 5 µm and two screens with rod-like shape grains and sizes 500 nm and 1-8 µm. The phosphors were deposited by the sedimentation method. It was found that the influence of the grains shape on image quality is more important than the grain size. The rod-like grains show higher noise levels, at low frequencies. The influence of grains size, between 50 nm, 200 nm, and 5 µm, is negligible on the normalize noise power spectrum (NNPS) at higher spatial frequencies due to structural non-uniformities. The spherical grains exhibited higher DQE values. [ABSTRACT FROM AUTHOR]

Phase-pure orthorhombic α′- and monoclinic β-Sr2SiO4 and its Ce3+- or Eu2+-doped versions are prepared by reaction of stoichiometric amounts of SrCO3, SiO2, CeO2 or Eu2O3 in the presence of 1 wt% H3BO3 or 1-50 wt% SrCl2 as fluxes in different atmospheres (1200-1400 °C, 4 h; in air, vacuum, 5% H2/N2, or 25% H2/N2). [ABSTRACT FROM AUTHOR]

Abstract: Ca1− x Eu x Al4O7 (x =0, 0.002, 0.01, 0.02, 0.05, 0.1) and Ca1−2 x Eu x Na x Al4O7 (x =0.002, 0.02, 0.05, 0.1) crystalline phosphor powders have been synthesized by modified Pechini method and their spectroscopic properties at room and liquid nitrogen temperature were measured. Excitation spectra of synthesized materials contain broad band attributed to ligand to metal, O2−→Eu3+, charge transfer absorption and narrow lines related to 7F0→5D J , 5H J , 5L J , 5G J transitions of europium ions. Upon excitation at 395nm, the Eu3+-doped calcium dialuminates exhibit red photoluminescence due to parity forbidden f–f intra-configurational transitions with the most intense component at 612nm resulting from the 5D0→7F2 hypersensitive transition. The quantum efficiency of the powders emissions does not exceed 12%. The luminescence decay kinetics reveals that some quenching appears for higher concentrations. Site selective spectroscopy disclosed the presence of at least two well defined individual spectroscopic sites of Eu3+ and increasing disturbance of their local symmetries with raising concentration of the activator was observed. The increasing symmetry disorder led to a significant asymmetrical broadening of the luminescence lines at higher concentrations. Concentration dependence of the luminescence kinetics of the two diverse Eu3+ ions is different, as only one of them, with the characteristic luminescence at 579.5nm, exhibits shortening of the decay time at higher Eu contents. The inexpensive CaAl4O7:Eu powders are potentially good candidates for photonics applications. For Eu, Na co-doped powders the Eu3+ ions producing emission at 579.7nm dominates strongly over those with luminescence at 577.2nm. [Copyright &y& Elsevier]

The remote temperature readout capability offered by luminescent thermometry has high application potential. Designing thermometers with predefined thermometric parameters is only possible by understanding the processes responsible for temperature-induced changes in the spectroscopic properties of phosphor. One of the key factors, that should be considered, is the influence of the morphology of the phosphor on their spectroscopic properties. In this work, we present for the first time an analysis of the influence of material morphology on the thermometric properties of a ratiometric luminescent thermometer based on the luminescence intensity ratio of 2E→4A 2 to 4T 2 →4A 2 emission bands in Gd 3 Ga 5 O 12 :Cr3+ nanocrystals, microcrystals and optical ceramics. As shown, limitations in the thermal coupling between the 2E and 4T 2 levels occurring in the cryogenic temperature range allowed to achieve a relative sensitivity of 5.8%/K at 11 K in optical ceramics compared to 2.6%/K and 1.95%/K in microcrystals and nanocrystals, respectively. • Thermometric properties of Gd 3 Ga 5 O 12 :Cr3+ were investigated. • Nanocrystalline, microcrystalline and optical ceramic were compared. • Supersensitive thermometer operating in a cryogenic temperature range was presented. [ABSTRACT FROM AUTHOR]

We show the opportunity for tuning of the spectral position of the Mn4+ red emission in the series of double perovskites, Ba 2 LaNbO 6 :Mn4+, Ba 2 La(Nb 0.8 ,Zr 0.1 ,W 0.1)O 6 :Mn4+, and Ba 2 La(Zr 0.5 ,W 0.5)O 6 :Mn4+ with increasing chemically induced symmetry disturbance. Such a disorder appeared attractive to engineering phosphors for pressure sensors or horticultural applications, for instance. The goal of the present research, not yet systematically addressed in the literature, was to unveil the correlation between chemically induced controlled crystal lattice distortion and the luminescence of Mn4+. For this purpose, the luminescence of these phosphors was methodically investigated at different pressures and temperatures. A pressure-induced redshift of photoluminescent lines with the rate of − 4 cm−1/kbar was found within the 0–230 kbar range, and the emission peak moved from 685 to 740 nm then. Furthermore, the cationic disorder allowed tuning of the Mn4+ luminescence making it useful for horticultural applications with a better fit between the emission wavelength and the strong chlorophyll absorption in the deep red part of the spectrum. The Mn4+ energy levels were computationally determined using the exchange charge model of the crystal-field theory which allowed for a deeper understanding of the experimental results. We found a correlation between the introduced disorder of the cationic subsystem and the energy of the Mn4+ emitting 2E g level (R-line) as well as its intensity. This research brought a deeper understanding of the Mn4+-activated phosphors and, in turn, provides tips for a prudent search of materials for advanced practical uses. [Display omitted] • The Ba 2 La(Nb 1–2x Zr x W x)O 6 :Mn (x = 0;x = 0.1;x = 0.5) isostructural phosphors are reported. • The influence of pressure and temperature on the luminescence of Mn4+ is presented. • Effects of chemically induced partial cation substitution are investigated. • Theoretical studies support the understanding of the experimental dependencies. • The findings provide tips for a deliberate design of phosphors for advanced uses. [ABSTRACT FROM AUTHOR]

Review: [discussion of the properties of the broad-band luminescence around 425 nm in the temp. [ABSTRACT FROM AUTHOR]

Abstract: Nanocrystallic europium-activated lutetium oxide (Lu2O3:Eu) is a strong candidate for use in digital medical imaging applications, due to its spectroscopic and structural properties. The aim of the present study was to investigate the imaging and efficiency properties of a 33.3mg/cm2 Lu2O3:Eu scintillating screen coupled to a high resolution RadEye HR CMOS photodetector under radiographic imaging conditions. Since Lu2O3:Eu emits light in the red wavelength range, the light emission efficiency and the imaging performance were compared with results for a Gd2O2S:Eu phosphor screen. Parameters such as the Absolute Efficiency (AE), the X-ray Luminescence Efficiency (XLE), and the Detector Quantum Gain (DQG), were investigated. The imaging characteristics of Lu2O3:Eu nanophosphor screen were investigated in terms of the Modulation Transfer Function (MTF), the Normalized Noise Power Spectrum (NNPS) and the Detective Quantum Efficiency (DQE). It was found that Lu2O3:Eu nanophosphor has higher AE and XLE by a factor of 1.32 and 1.37 on average, respectively, in the whole radiographic energy range in comparison with the Gd2O2S:Eu screen. DQG was also found higher in the energy range from 50kVp to 100kVp and comparable thereafter. The imaging quality of Lu2O3:Eu nanophosphor coupled to the CMOS sensor was found to outmatch in any aspect in comparison with the Gd2O2S:Eu screen. These results indicate that Lu2O3:Eu nanophosphor could be considered for further research in order to be used in medical imaging applications. [Copyright &y& Elsevier]

Abstract: Ceramic specimens of singly doped Lu2O3:Tb, and doubly activated Lu2O3:Tb,Ca, Lu2O3:Tb,Hf and Lu2O3:Pr,Hf were prepared and their thermoluminescent properties were investigated. After irradiation with X-rays or deep-UV photons the singly doped Lu2O3:Tb was found to produce a glow curve with a few thermoluminescent bands spread across the temperature range of 50–450°C. (Tb,Ca) co-doped material produced basically one strong thermoluminescent band peaking at around 120°C and thus was able to produce persistent luminescence lasting about 10h, as visible to the human eye. In the (Tb,Hf) co-doped ceramics the thermoluminescence at around 100°C was seen as a vestige only and was responsible for persistent emission lasting merely a few minutes. Instead, a strong thermoluminescence glow band at around 250°C appeared. Its intensity faded by about 10% after 6hours in the dark. Lu2O3:Pr,Hf co-doped ceramics also showed intense thermoluminescence with the main components at around 200°C and 270°C. The latter was found not to fade in time, while intensity of the former dropped by about 7–8% after 6h. All these effects were observed in ceramics processed at temperatures as high as 1700°C. It is proposed that high temperature of processing is necessary as only then clustering of individual defects occurs and the energy released upon heating can diffuse towards the nearby located emitting center efficiently. [Copyright &y& Elsevier]