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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]

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]

Comparison of the luminescent properties of nanopowder, single crystal and single crystalline film of Pr 3+ doped Pr-doped Lu 3 Al 5 O 12 garnet (LuAG:Pr) prepared by the different technological methods is performed in this work using the time-resolved emission spectroscopy under excitation by synchrotron radiation with an energy of 3.7–25 eV at 300 K and 10 K. The notable differences in the properties of the Pr 3+ luminescence are observed in LuAG:Pr crystals and films caused by involving the Lu Al antisite defects and oxygen vacancies in crystals and Pb 2+ flux related dopant in films in the excitation processes of the Pr 3+ luminescence. At the same time, we have also found that the influence of host defects on the Pr 3+ luminescence is significantly smaller in the LuAG:Pr nanopowders. [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]

Tb 3+ and Yb 3+ co-doped calcium aluminate powders: Ca 1−x−y Yb x Tb y Al 4 O 7 (x = 0.02–0.06; y = 0.02), Ca 1−x−y Yb x Tb y Al 4 O 7 (x = 0.03, y = 0.01–0.07), Ca 1−x−y Yb x Tb y Al 4 O 7 (x = 0.01–0.05, y = 0.01) were synthesized by a modified Pechini citrate process and their optical properties were investigated. Upon excitation at 245 nm all studied samples yielded relatively strong Tb 3+ luminescence corresponding to the 5 D 4 → 7 F J and 5 D 3 → 7 F J transitions with the dominant component around 542 nm. The direct excitation of two Yb 3+ ions at 980 nm led to cooperative sensitization of the Tb 3+ 5 D 4 level giving rise to its green up-conversion luminescence. The up-conversion emission was also observed from higher 5 D 3 level of Tb 3+ , which is rather rare in high phonon frequency host materials. The effect of activator concentration and charge compensation by co-doping with Na + ions on luminescence properties were studied. It was found that Na + addition lowers disturbance/distribution of activator ions local symmetries and enhanced Stokes Tb 3+ photoluminescence brightness, while the up-conversion emission intensity does not appear to change noticeably then. [ABSTRACT FROM AUTHOR]

Abstract: Calcium aluminate powders co-doped with Yb3+ and Eu3+: Ca1−x−y Yb x Eu y Al4O7 (x = 0.02–0.06; y = 0.02), Ca1−x−y Yb x Eu y Al4O7 (x = 0.05, y = 0.01–0.07) were synthesized by a modified Pechini citrate process and their optical properties at 298 K and 77 K were investigated. Direct excitation of Yb3+ by means of 2F7/2 → 2F5/2 absorption at 980 nm leads to bluish-green luminescence centered around 488 nm due to the cooperative emission of Yb3+ and red emission of Eu3+ corresponding to 5D0 → 7F J (J = 0–4) transitions. The near-infrared to red up-conversion luminescence of Eu3+ was assigned to a cooperative sensitization mechanism. The effect of activators concentration and charge compensation by co-doping with Na+ ions on luminescence properties were studied in detail. Na+ addition led to narrowing of luminescence bands, suggesting smaller disturbance/distribution of activator ions local symmetries. This was associated with significantly enhanced luminescence brightness of Eu3+ under UV excitation and, surprisingly, with noticeably reduced efficiency of Eu UC emission upon near-infrared excitation. It was also concluded that Yb3+ pairs transfer preferentially their excitation energy to Eu3+ ions with the local symmetry perturbed by certain defects present in the crystal lattice. [Copyright &y& Elsevier]

Abstract: Two series of calcium gallate phosphors: Ca1−x Eu x Ga4O7 and Ca1−2x Eu x Na x Ga4O7 (x=0, 0.002, 0.01, 0.02, 0.03, 0.05) were synthesized by a modified Pechini method and their optical properties at 298 and 77K were investigated. In undoped CaGa4O7 upon 255nm excitation a bluish white emission (λ max=500nm) followed by an afterglow of the same color lasting for 10–20s was observed. Eu3+-doping quenched the host-related luminescence and the characteristic red emission of the dopant with maximum at 613nm appeared. Its excitation spectrum consisted of a broad band assigned to ligand to metal, O2−→Eu3+, charge transfer absorption and narrow lines arising from intraconfigurational transitions within the 4f6 states of Eu3+ ion. The effects of Eu3+ concentration and Na+ co-doping on the luminescence properties and decay kinetics were studied. Low temperature emission spectra showed that Eu3+ ions are positioned in environments of different symmetries. Their relative populations changed with the activator content. Co-doping with Na+ ions led to a remarkable reduction of the number of Eu3+ sites as well as to noticeable improvement of the luminescence brightness though it did not affect the decay time of the emission. The quantum efficiencies of singly doped CaGa4O7:Eu3+ were very low (in the range of 1–3.7%). Na+ co-doping improved this parameter leading to the highest efficiency of 11% for CaGa4O7:3%Eu3+,3%Na+. [Copyright &y& Elsevier]

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]

Powders and thin films of nanocrystalline yttrium disilicate (Y2Si2O7) doped with Ce3+ have been prepared by a sol–gel method. Structure and morphology of the synthesised samples have been determined and spectroscopic properties compared. The triclinic α-Y2Si2O7 form (space group P 1-) for the powders annealed between 1000°C and 1200°C has been found. A total conversion into a thortveitite-type monoclinic β-Y2Si2O7 polymorph after annealing of powder samples at 1400°C (space group C2/m) has been observed. In the case of films even at 1300°C the basically pure triclinic α-Y2Si2O7 phase was observed with luminescent spectroscopy. The influence of grain size, controlled by thermal treatment, on the structure and luminescence properties of the fabricated materials are presented and discussed. [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: A comparative analysis of the luminescent properties of YAG and YAG:Ce nanopowders (NP) in comparison with single crystalline film (SCF) and single crystal (SC) analogues was performed under excitation by a pulsed synchrotron and X-ray radiation. It was shown that the natural defects concentration in NP was between the SC with a large (∼0.18–0.19at.%) concentration of YAl antisite defects (AD) and SCF of these garnets where YAl AD were completely absent. At the same time, Ce3+ doped YAG NP showed luminescent properties close to those of YAG:Ce SCF. [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]

Nanocrystalline powders of Lu2O3:Eu with the activator content varying in the range of 0.2–10% were prepared through a combustion technique. The powders were only slightly agglomerated and the size of crystallites were about 30 nm. Some of the powders were co-doped with Mg, Ca, Sr, Ba, La of various concentrations. Such powders were cold-pressed and sintered at 1750°C for 5 h in vacuum. X-ray-excited luminescence spectra of both the powders and the sintered ceramics were recorded and the efficiency was compared to the commercial standard Gd2O2S:Pr,Ce,F X-ray phosphor. It was found that the nanocrystalline powders of Lu2O3:Eu,Ca emit photons four-times less than the commercial micron-sized Gd2O2S:Pr,Ce,F powder. In the case of sintered materials the emission efficiency from our Lu2O3:Eu5%, Ca was roughly equal to the efficiency of the commercial-sintered Gd2O2S:Pr,Ce,F. The co-doping ions were shown to have various effects on the transparency of the sintered Lu2O3:Eu. Mg hindered the sintering process producing completely opaque pellets. Other ions facilitated the sintering course and the best results were obtained by co-doping the samples with 0.5% of Ba. Sr and La also significantly stimulated the sintering and the final pellets were only slightly cloudy. [Copyright &y& Elsevier]

Uranium(3+) doped Cs2NaYBr6 single crystals with a 2.1 and 0.09 mol% U3+ concentration have been obtained by the Bridgman–Stockbarger method. The U3+ ions replaced the Y3+ ions at an octahedral site of Oh symmetry. Luminescence spectra of the crystal were recorded at 4.2 K. The emission bands observed in the visible and near infrared regions have been assigned to transitions from the lowest components of the 4G7/2 and 4F3/2 multiplets to the crystal-field components of the 4I9/2 ground state. Absorption spectra were recorded in the 3900–35,000 cm−1 range at 4.2 K. The analysis of these spectra enabled the assignement of 28 energy levels, which were fitted to seven parameters of an empirical Hamiltonian representing the combined atomic and crystal-field interactions, with a rms deviation of 43 cm−1. The energies of the most prominent vibronic features have been measured and assigned to the specific vibrational modes of the UCl63− moiety or to lattice modes. Above 14,000 cm−1 vibronic transitions associated with the electric dipole allowed 5f3–5f26d1 transitions were observed. The unresolved zero-phonon lines are accompanied by a number of vibrational progressions combined with the even S1(a1g) mode. [Copyright &y& Elsevier]

Decay kinetics and X-ray diffraction patterns of Lu 2 O 3 :Eu with concentration of the dopant spanning 0-20% were measured for two series of materials with crystallites sized of 13 nm and 35 nm. For the series of smaller crystallites a very significant concentration quenching was observed, while for the larger crystallites the effect was minor only. Detailed structural analysis made it possible to postulate that this effect is related to an inhomogeneous distribution of Eu 3+ ions within the smaller crystallites. [ABSTRACT FROM AUTHOR]

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]

This work is dedicated to the preparation and characterization of the radio-, thermo-, and photoluminescent properties of Lu2O3:Eu and Lu2O3:Tb nanopowder (NPs) scintillators, prepared by means of hydrothermal processing, and their film analogues made of these NPs by the spin coating method. The luminescent properties of NPs and films were characterized by cathodoluminescence (CL), photoluminescence (PL), X-ray excited radioluminescence (RL), and thermoluminescence (TL) at low and high temperatures. In Lu2O3:Eu NPs and films, mostly the luminescence of Eu3+ ions occupying the C2 site of the host, with the most intensive peaks at 611.6 nm and a decay time of 1.5 ms, was observed. On the contrary, two types of Tb3+ centers in the C2 and C3i sites with the main emission lines at 542.4 and 544.0 nm and the corresponding 4f→5d excitation bands at 270 and 305 nm and decay times of t1/e = 2.17 and 3.96 ms were observed in the case of Lu2O3:Tb NPs and films. Indications were noted that Tb3+ in the C3i symmetry position was most active in the CL spectra of Lu2O3:Tb NPs and a respective film. Thermoluminescent peaks at 110 °C and 170 °C for Lu2O3:Eu NPs and at 75 °C and 120 °C in Lu2O3:Tb NPs were observed corresponding to the hole and electron traps, respectively. Significantly different onsets of temperature quenching of Eu3+ and Tb3+ luminescence in Lu2O3:Eu and Lu2O3:Tb NPs were found at ~90 °C and ~320 °C, respectively. [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: Bulk alkaline earth fluorides co-doped with optically active ions are prominent materials for luminescent applications. However, for phosphor materials the changeover to the nanoscale is a tightrope walk between achieving desirable features of small particles such as reduced light scattering and unwanted drawbacks such as a high surface defect concentration which is likely to result in quenching of luminescence. A new preparation route via ionic liquids allows obtaining pure and oxygen-free alkaline earth fluorides co-doped with Eu3+ and Gd3+ on the nanoscale with excellent quantum cutting abilities. [Copyright &y& Elsevier]

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]

BaHfO 3 sintered ceramic scintillators doped with various Pr concentrations (0–1 mol%) were synthesized at 1700 °C in N 2 –H 2 atmosphere. XRD, SEM and photo-luminescent techniques at various temperatures (40 K to 550 K) were employed to reveal properties of the BaHfO 3 :Pr ceramics. Results of spectroscopic investigation indicate that the luminescence is connected almost exclusively with decay of the 3 P 0 level, while the emission from 1 D 2 is hardly seen even for higher Pr 3+ concentrations. However, the intrinsic emission of BaHfO 3 matrix, related with defects or impurities, seems to compete with the emission of Pr 3+ ions. The 3 P 0 luminescence decays give time constant of about 25–32 μs in the 40–550 K range of temperatures, while the 1 D 2 decay time depends on the dopant concentration and gets shorter above 300 K for 1% specimen due to a cross relaxation process between Pr 3+ ions. [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: Comparative analysis of the luminescent properties of Y3Al5O12:Ce (YAG:Ce) transparent optical ceramics (OС) with those of single crystal (SC) and single crystalline film (SCF) analogues has been performed under excitation by pulsed synchrotron radiation in the fundamental absorption range of YAG host. It has been shown that the properties of YAG:Ce OC are closer to the properties of the SCF counterpart, where YAl antisite defects are completely absent, rather than to the properties of SC of this garnet with large concentration of YAl antisite defects. At the same time, the luminescence spectra of YAG:Ce OC show weak emission bands in the 200–470nm range related to YAl antisite defects and charged oxygen vacancies (F+ and F centers). YAG:Ce ОС also possesses significantly larger contribution of slow components in the Ce3+ luminescence decay under high-energy excitation in comparison with SC and SCF of this garnet due to the involvement of antisite defects, charged oxygen vacancies as well as boundaries of grains in the energy transfer processes from the host to the Ce3+ ions. [ABSTRACT FROM AUTHOR]

The sol–gel derived synthesis of TiO2 films doped with Lu2O3:Tb3+ nanocrystallites and deposited on quartz or silicon substrates has been described. Their morphology have been determined by the SEM techniques. The transmission, photoluminescence and cathodoluminescence spectra have been measured. The emission decays have been measured and lifetimes for starting nanocrystalline powders and embedded nanocrystallites have been determinated. A strong influence of TiO2 matrix on the emission properties of embedded Lu2O3:Tb3+ nanocrystallites was found. [Copyright &y& Elsevier]