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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]

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]

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]

Efforts to obtain translucent pellets of BAM for Martian UV-dosimeter were undertaken. Sinterability of both commercial BAM powder and a Pechini-derived one was examined. The commercial phosphor sinters with difficulty only, while the one made with Pechini procedure sinters easily and translucent pellets could be obtained in such a way. Vacuum sintering at 1750 °C for 15 h was also enough to fully convert Eu3+ into Eu2+ in the sintered pellets without the necessity of using hydrogen-containing gas. The spectroscopy of the sintered BAM differs noticeably from its commercial powdered counterpart. The excitation is much more flat in the entire UV and especially strong enhancement of the excitation efficiency is observed in the near-Vis part of the UV region. Decay kinetics is exactly the same for commercial powder and sintered ceramic, which proves the lack of luminescence quenching in the latter. The sintered pellets of BAM made in our laboratory show mechanical and spectral characteristics, which make the material suitable for Martian UV-dosimeter. [Copyright &y& Elsevier]

The size effect of nanoparticles on optical properties of Lu2O3:Eu3+ was investigated. No pronounced effect was observed for structure of emission spectra. It was found that effect is mainly manifested in the decay profiles of Eu3+ emission. We have noticed that the decay times were almost the same for low concentrations of Eu3+ ions. It is concluded that the size effect is associated with agglomeration of Eu3+ in nanorange particles. [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]

Using combustion synthesis and urea as a fuel, Lu2O3 powders were prepared and their morphology defined with HRTEM measurements. The powders were sintered at 1700 °C for 5 h and the microstructure of the obtained ceramics was characterized. It turned out that the as-made powders were strongly agglomerated compositions with a mean particle size of 15–25 nm. High-temperature sintering caused some increase in the size of the crystallites, diameter increased to an average of 25–35 nm. However, domains of about 200–300 nm diameter were formed. These were separated by relatively broad transient regions. The inter-domain regions of rather ample thickness are blamed for relatively high scattering of the sintered ceramic specimens. The formation of the domains is correlated to the existence of agglomerates in the urea-derived nanoparticulate powders. [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]

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]

Abstract Perfectly transparent ceramics of La 0.4 Gd 1.6 Zr 2 O 7 doped with either Eu3+ or Pr3+ ions were prepared by high-temperature vacuum sintering. Results of the Rietveld structure refinement and spectroscopic properties of the ceramics are presented and discussed in details. Photoluminescence characteristics support the non-uniformity in the crystal structure of ceramics. X-ray excited luminescence of La 0.4 Gd 1.6 Zr 2 O 7 :Eu was rather inefficient and the Pr-doped ceramics showed no Pr-related radioluminescence. Instead they produced Eu3+ emission characteristic for Gd 2 O 3 :Eu phase not detected in X-ray diffraction patterns. Highlights • Structure refinement of La 0.4 Gd 1.6 Zr 2 O 7 transparent ceramics revealed non-uniformity of its crystal structure. • Photoluminescence confirmed the multisite occupancy of the activator in Eu3+/Pr3+-doped La 0.4 Gd 1.6 Zr 2 O 7 transparent ceramics. • The Eu3+ presence as well as gadolinia contamination was analyzed through photo-/radioluminescence. [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]