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Li2SO4 or (Li2SO4 + SiO2)-mixture fluxes were used to prepare a Lu2O3:Eu powder phosphor as well as an undoped Lu2O3 utilizing commercial lutetia and europia as starting reagents. SEM images showed that the fabricated powders were non-agglomerated and the particles sizes varied from single microns to tens of micrometers depending largely on the flux composition rather than the oxide(s)-to-flux ratio. In the presence of SiO2 in the flux, certain grains grew up to 300-400 μm. The lack of agglomeration and the large sizes of crystallites allowed making single crystal structural measurements and analysis on an undoped Lu2O3 obtained by means of the flux technique. The cubic structure with a = 10.393(2) Å, and Ia3 space group at 298 K was determined. The most efficient radioluminescence of Lu2O3:Eu powders reached 95%-105% of the commercial Gd2O2S:Eu. [ABSTRACT FROM AUTHOR]

Sintered nanoceramics of Pr-doped lanthanum hafnate, La2 Hf2 O7: Pr, were prepared by means of a high-pressure sintering technique using nanopowders made by Pechini method. Structure, morphology, and spectroscopic properties of the ceramics compared to the starting powder are presented and discussed. Emission and excitation spectra recorded at room temperature as well as at 7 K using synchrotron radiation are presented together with results of luminescence kinetics measurements. In ceramics, at 7 K, the Pr3+ luminescence from 3P0 (blue-green, green, and red region) and 1D2 (red) levels is accompanied by a broad-band emission located in the 380-530 nm range of wavelengths, whereas powders gives only the Pr3+-related luminescence. Depending on the excitation wavelength, the broad-band emission maximum moves between 430 and 470 nm indicating superposition of at least two components. In sintered nanoceramics, the lifetimes of Pr3+ emissions from 3P0 and 1D2 levels were by 10%-20% shorter compared to the powder. The existence of different luminescence centers was proved by the selective emission decays examination. The fast 5 d → 4 f luminescence of Pr3+ was not observed from either of the two types of La2Hf2O7:Pr materials. [ABSTRACT FROM AUTHOR]

Lu2O3:Pr,Hf ceramics were investigated using mainly thermoluminescence (TL) technique. Their ability to efficiently store energy acquired upon irradiation with X-rays was proven. The best TL performance was achieved for compositions containing 0.025%-0.05% of Pr and about 0.1% of Hf. Further enhancement of TL efficiency was attained by increasing the temperature of sintering of the ceramics up to 1700 °C and applying reducing atmosphere of forming gas. It was also proven that fast cooling after the sintering at 1700 °C significantly enhanced the storage phosphor performance. TL glow curve contained three components peaking around 130, 250 and 350 °C. Among them, the one at 250 °C contributed the most to the total TL. [ABSTRACT FROM AUTHOR]

Abstract: Powders of calcium yttrium silicate, Ca3Y2(Si3O9)2, containing 0.1–3% Tb3+ were prepared using a sol-gel method and characterized with XRD, IR, UV–vis and UV–VUV spectroscopies at room temperature and 10K. Structural analysis revealed pure monoclinic phase of Ca3Y2(Si3O9)2 after heat-treatment at 1000°C. Infrared spectroscopy showed that between 800 and 900°C a short-range structural organization of the components proceeded, yet without crystallization. A strong emission of Tb3+ had been observed both in the green part of the spectrum due to the 5 D 4→7 F J transitions and in the blue-violet region owing to the 5 D 3→7 F J radiative relaxation. The color of the light could be tuned from yellowish-green to bluish-white both by means of the dopant content and the temperature of synthesis. Efficient luminescence of Tb3+-doped Ca3Y2(Si3O9)2 phosphors could also be obtained upon stimulation with vacuum ultraviolet synchrotron radiation demonstrating that an energy transfer from the host to the Tb3+ ions takes place. [Copyright &y& Elsevier]

Abstract: Powder samples of Lu2O3 with the following mean size of crystallites: 6nm, 50nm and 150nm were structurally and spectroscopically characterized. XRD patterns and TEM images as well as luminescence, luminescence excitation and reflectance spectra were recorded. The measurements revealed profound differences in luminescent properties of the three specimens and basically all the variations scaled with the size of crystallites. For larger particles complex luminescence spectra with at least four components around 255nm, 317nm, 340nm and 450nm were observed. For the smallest crystallites only the last two, defect-related constituents could be recorded. Excitation into the host-lattice fundamental absorption, below 210nm, was progressively less effectively converted into luminescent photons as the crystallites were getting smaller. Excitation and reflectance spectra did not show any signs of quantum confinement down to 6nm. [Copyright &y& Elsevier]

Abstract: Fabrication procedure of nanocrystalline Lu2O3:Eu powders from organic–inorganic emulsion is presented and the behavior of the precipitate upon heat-treatment is analyzed. It is proved that heating at 800–850°C converts the raw material into Lu2O2SO4:Eu, which decomposes further to Lu2O3:Eu when heated at 1000°C or above. Research with synchrotron radiation revealed that free exciton is able to transfer effectively its energy to Eu3+ ions in Lu2O3:Eu nanosized powder, which is in contrast to the findings for micron-sized ceramics of the same composition. [Copyright &y& Elsevier]

Abstract: Nanocrystalline powders of Y3Al5O12:Ce (YAG:Ce) were prepared using Pechini technique and precipitation with urea at 80–90°C. It was shown that material obtained using Pechini procedure, after heating at 900–1000°C is crystallographically pure, while that made with urea is contaminated with Y4Al2O9 and YAlO3. For all powders, heating at reducing atmosphere of nitrogen–hydrogen mixture at 1000°C caused a red shift of the Ce3+ luminescence by about 20–25nm. The effect was stronger for the powder prepared with urea. Also this powder was characterized by a longer decay time of the Ce3+ emission indicating the treatment at reducing atmosphere diminished nonradiative relaxation probability of the excited electrons. [Copyright &y& Elsevier]

Abstract: Y2SiO5 doped with Ce3+ was successfully prepared at 1300°C with the aid of Li2SO4 flux. SEM and TEM images proved that the sizes of particles making-up the powder are in the range of 1–10μm. A small fraction of grains is nanosized. EDS spectra proved that the distribution of Y, Si and Ce is uniform. Luminescence spectra show typical broad Ce3+ luminescence in Y2SiO5 host, which peaks around 420nm. The emission decays with the time constant of about 40ns. [Copyright &y& Elsevier]

Abstract: Synthesis of Y3NbO7:Er powders with the aid of Li2SO4 flux is reported and spectroscopic properties of the resultant powders are presented. The dopant content varied in the range of 0.1–15at%. The materials crystallized in the fluorite-type cubic structure in which all the metal ions—Y, Nb, and Er—randomly occupy the same site offered by the host lattice and the O-vacancy is also randomly distributed within the metal surrounding. Transmission electron microscopy images revealed that the agglomeration of particles is very low and the sizes of the grains are around 500nm. Selected area electron diffraction patterns proved that each grain is monocrystalline. Absorption, excitation, and emission spectra are characterized by relatively broad structures related to the Er3+ ion. The broadening results from some inhomogeneity of the activator ion surroundings related to the specific structure of the host lattice. When the Er content is only 0.1% both photoluminescence and up-converted emission are dominated by a green luminescent band around 550nm. However, the efficiency of up-conversion is very low . With increasing concentration of the dopant, a red band located around 665nm appears and becomes systematically stronger. In up-converted emission, the intensity of the red band surpasses the green one when the Er concentration exceeds 5%. For low concentrations, the up-conversion occurs through a sequential absorption of two infrared (IR) (980nm) photons from the excitation beam by Er3+ ion through excited-state absorption mechanism. For higher concentrations, the energy transfer between two neighboring excited Er ions plays dominant role. Surprisingly, the mechanism of up-converted low-intensity luminescence from 2H11/2 state seems to diverge from the mechanism characteristic for the 4S3/2 level, which conclusion comes from different slopes of the double-log relationships. [Copyright &y& Elsevier]

Abstract: Radioluminescence and persistent luminescence from Lu2O3 doped with Eu3+ ions (0.05–5%) were investigated. The radioluminescent emission is almost totally due to Eu3+ ions occupying the C2 symmetry site of Lu2O3 host, and the luminescence from Eu ions placed in S6 site makes only 1–3% of the total. However, Eu3+ ions occupying the S6 site becomes abnormally active in persistent luminescence. The effect reached its peak for 0.2% and 0.5% samples, for which the afterglow luminescence occurred mostly through Eu in the S6 site. This effect is indeed surprising, since only 25% of metal sites in Lu2O3 possess the S6 symmetry, while 75% sites are of the C2 symmetry. For strongly diluted materials containing less than 0.2% of the activator, the effect of unusually significant afterglow from Eu in S6 site becomes slightly less profound. For samples containing 3% and 5% of Eu this effect practically disappears. [Copyright &y& Elsevier]

Abstract: Eu-doped barium hafnate powders, BaHfO3:Eu, prepared with ceramic method have quite peculiar spectroscopic properties, which can be significantly altered changing the dopant concentration as well as preparation atmosphere. When synthesis is performed in a reducing atmosphere, a fraction of Eu gets reduced and produces a broad-band emission peaking around 480nm. Due to a partial overlapping of the excitation spectra of Eu3+ and Eu2+ luminescence, the emission colour can vary between bluish green, when only Eu2+ is excited, red when solely Eu3+ is stimulated and white upon simultaneous excitation of both Eu3+ and Eu2+ activator ions around 290nm. Upon X-ray excitation only Eu3+ luminescence is produced. Radioluminescence of undoped BaHfO3 consists of a broad-band peaking around 410nm, which disappears when Eu enters the host. Materials prepared in a reducing atmosphere do not show any phase separation even for higher Eu concentrations. [Copyright &y& Elsevier]

Abstract: Raw powders of BaHfO3:Ce were prepared with modified Pechini process and were calcined in the 650–1700°C range of temperatures, at different atmospheres – air, vacuum and nitrogen–hydrogen mixture. The powders were converted into sintered ceramics by vacuum sintering. The materials were characterized by XRD, TEM, photoluminescence and radioluminescence spectroscopy. UV-VUV excitation spectra were recorded using synchrotron radiation. Excitation spectra proved that atmosphere of preparation significantly influences the host-to-activator energy transfer, which is the most efficient for materials made in reducing conditions. Also radioluminescence efficacy was found to be superior for materials prepared in such conditions. [Copyright &y& Elsevier]

Having proven that the temperature range of luminescent thermometers can be greatly widened by combining the intra‐ and interconfigurational transitions of the Pr3+, the possibility to manage important thermometric parameters by bandgap engineering and variation of energy of excitation photons are examined. Partial replacement of Ge with Si to form Sr2(Ge,Si)O4:Pr is very useful to manage these luminescence thermometer properties. This allows control of the range of temperatures within which the 5d1→4f Pr3+ luminescence can be detected. Also, excitation energy appears to affect the thermometer's performance. These allow adjustment of the range of temperatures that can be measured with the highest accuracy, reaching the spectacular value of Sr = 9.2% K−1 at 65 K for a Sr2(Ge0.75,Si0.25)O4:0.05%Pr3+ thermometer upon 244 nm excitation. For the first time, it has been proven that excitation energy may significantly affect the performance of luminescence thermometers. In Sr2(Ge0.75,Si0.25)O4:0.05%Pr3+ the highest relative sensitivity shifts from 65 K upon 244 nm excitation (Sr = 9.2% K−1) to 191 K upon 253 nm excitation (Sr = 3.97% K−1). This occurs despite both excitation wavelengths fitting within the 4f→5d1 excitation band. This paper shows that bandgap management is useful to effectively design new luminescent thermometers. [ABSTRACT FROM AUTHOR]

In this study, we present a comprehensive analysis of the optical properties of colloidal gold nanoshells (NSs) with varying thicknesses of the gold layer and an additional silica layer. Our results demonstrate that the spectral position of the localized plasmon resonance in NSs is very sensitive to the above parameters. Furthermore, we observe that the silica coating has a notable impact on the stability of colloidal systems. We supplement our experimental results with theoretical calculations, revealing the relative contributions of the absorption and scattering to the overall extinction as a function of the gold layer thickness. The calculations also provide an insight into the origin of spectral broadening in the case of clustered NSs. Our findings hold significant potential for the design of hybrid materials intended for diverse applications, including refractive-index sensing, metal-enhanced fluorescent emission (MEF), and surface-enhanced Raman scattering (SERS). [Display omitted] • The stringent control of synthesis parameters significantly influences the quality of obtained nanoshells. • The silica coating on metallic nanoparticles notably enhances their stability in solution. • Nanoshells with a thinner gold layer are more suitable for use in sensors relying on LSPR shifts induced by refractive index variations on their surface. • Nanoshells with a thin gold layer have shown the highest absorption contribution compared to scattering, making them particularly well-suited for applications like photothermal therapy. • The extinction spectra calculated for nanoshells dimers and trimers have shown strong dependence on the incident light polarization and propagation direction. [ABSTRACT FROM AUTHOR]

Oxyorthosilicates have long history in luminescent applications e.g. as phosphors, scintillators and in emerging technologies like luminescence thermometry. In this study we report detailed research on the thermoluminescent (TL) properties of Y 2 (Ge x ,Si 1-x)O 5 :Pr. Despite regular TL measurements, T max -T stop , initial rise analysis, fading, decay of persistent luminescence, and dose effect are presented and analyzed. The possibility to deliberately manage the electron trap depths adjusting the Ge/Si ratio is explored. Glow curve of each composition consists of two main TL peaks. In the (Ge,Si) solid continuous distribution of trap energies is observed. Strong thermoluminescence is observed from all compositions after charging with X-ray radiation. Efficiency of charging traps with UV-C photons (fitting the 4f→5d 1 transition energy) lowers systematically as the Si content increases. A growing coupling of the excited 5d 1 level of Pr3+ and the host conduction band with the increase of Ge content is responsible for this effect. A scheme of the TL-related processes is presented using the vacuum referred binding energy (VRBE) approach for all the Y 2 (Ge x ,Si 1-x)O 5 :Pr phosphors. Image 1 • Effect of bandgap engineering in Y 2 (Ge x ,Si 1-x)O 5 :Pr phosphors on intrinsic traps parameters is presented. • Thermoluminescence dependence on energy of the charging radiation is examined. • Dependence of trap depths distribution on the host composition is disclosed. [ABSTRACT FROM AUTHOR]

Abstract: Lu2O3:Tb,Hf ceramics containing 0.1% of Tb and 0–1.5% of Hf were prepared in reducing atmosphere at 1700°C and their thermoluminescence properties were systematically studied. For comparison Tb,Ca co-doped specimen was also fabricated and investigated. The Tb,Hf ceramics shows basically a single TL band located around 180°C as found with heating rate of 15°C/min. Ceramics singly doped with Tb show complex TL glow curves indicating the presence of traps of very different depths. On the other hand Tb,Ca co-doping is beneficial for the development of shallow traps with the main TL band around 70°C. Hence, the aliovalent impurities, Ca2+ and Hf4+, strongly influenced the traps structure in Lu2O3:Tb ceramics, each of them in its own specific way. Isothermal decay of Lu2O3:Tb,Hf at 185°C was recorded and its shape suggest that multiple hole trapping occurs in the Lu2O3:Tb,Hf ceramics. Due to the different traps depths the Lu2O3:Tb,Hf ceramics possess properties typical for storage phosphors, while Lu2O3:Tb,Ca is a persistent luminescent material rather. [Copyright &y& Elsevier]

Depending on the dose of ionizing radiation, ScPO 4 :0.1%Eu3+ sintered ceramic presents significantly different thermoluminescent properties. Despite a thermoluminescent peak around 90 °C which appears upon small doses (up to tens of mGy) it also shows strong thermoluminescence at 240 °C but only after exposure to higher doses. In both cases, the thermoluminescence is generated by Eu3+ ions, which also serve as electron traps. Recognition of the relevant hole traps responsible for the thermoluminescent peaks needs more comprehensive research using such tools as advanced EPR spectroscopy at different temperatures. At room temperature, the thermoluminescence peak at 240 °C is very resistant to fading hardly showing any loss of intensity within 24 h. The peak at 90 °C fades continuously at ambient conditions and after 24 h its intensity drops to about 10% of its original strength. Hence, this component is responsible for the hours-lasting persistent luminescence of the ScPO 4 :0.1%Eu3+ ceramic. • Drastic dose-dependence of energy storage of ScPO4:Eu ceramics is presented. • Low doses produce one thermoluminescence peak, high doses gives two separate peaks. • AT high doses the high-temperature peak prevails the low-temperature one. [ABSTRACT FROM AUTHOR]

The effect of doping of Gd3+ ions into Ce: SrF 2 on luminescence properties was investigated in (Gd, Ce): SrF 2 nanoparticle powders synthesized via the co-precipitation method, which contained fixed amount of Ce3+ ions and variable amounts of Gd3+ ions. (Gd, Ce): SrF 2 nanoparticle powders showed UV range emissions under λ ex = 273 nm and λ ex = 298 nm excitation. Photoluminescence emission, excitation, and lifetime measurements revealed the existence of Ce3+ → Gd3+ radiative energy transfer and provided evidence to the prevailing effect of Ce3+ in excitation and emission in the (Gd, Ce) co-doped system due to the existence of fully allowed 4f-5d transitions. The presence of Gd3+ was shown to affect the crystal field and symmetry around Ce3+ ions and enhances the absorption efficiency by two-fold. Furthermore, (Gd, Ce): SrF 2 transparent ceramics with 13.2% of in-line optical transmittance in the UV spectral range was obtained via the vacuum hot-pressing method. The increase in the UV luminescence emission intensity of Ce3+ in presence of Gd3+, as well as the ability to process (Gd, Ce): SrF 2 as transparent ceramics, are what make (Gd, Ce): SrF 2 a promising material for optical applications in the UV region. • Radiative energy transfer from Ce3+ to Gd3+ ions in SrF 2 host material. • Increase in UV luminescence emission intensity of Ce3+ due to co-doping with Gd3+ and introduction of extra F− ions. • Fabrication of (Gd, Ce): SrF 2 transparent ceramics. [ABSTRACT FROM AUTHOR]

ScPO 4 :0.1%Eu3+ sintered materials were found to generate orange-red persistent emission following exposure to X-rays. A set of thermoluminescence techniques and isothermal decay measurements were used to study the mechanisms of the carriers' trapping and detrapping processes. The two main TL peaks at around 90 °C (363 K) and 160 °C (433 K) were found to result from so-called continuous distribution of trap depths. Room temperature fading proved that the persistent luminescence was connected with the strong TL peak at ∼90 °C (363 K). The persistent emission kinetics was characterized by a linear dependence of I −1(t). This was consistent with the continuous distribution of trap energies observed in the material. The main persistent emission components were located around 590, 620, and 720 nm. The most significant contribution was from the first and the third of them, resulting from the 5D 0 →7F 1 and 5D 0 →7F 4 transitions, respectively. • Orange-red persistent luminescence of ScPO 4 :Eu ceramics is presented for the first time. • Mechanism of carriers trapping is presented and hole and electron trapping centers are Eu3+ and O-ligand, respectively. • Comparison to similar ceramics of LuPO 4 :Eu is presented and discussed. [ABSTRACT FROM AUTHOR]

The employment of phosphors in luminescence thermometry is deemed one of the pivotal developments in the field. Besides the convenience of remote readings, phosphors may offer a plethora of other alluring benefits in this field. At present, one of the most paramount predicaments in this field involves developing an optical thermometer capable of functioning across an extensive temperature range encompassing hundreds of degrees while simultaneously delivering reasonable thermal sensitivity. As recently proven by us, the range of temperature readout can be significantly enhanced by the combination of intra- and interconfigurational transitions of Pr3+ while maintaining S r > 0.5 %/K across the whole temperature range. In this work, the idea has been extended using the combination of two dopants, Pr3+ and Tb3+, which exhibit minimal interference and instead demonstrate a combined impact of their respective temperature-dependent attributes across a range of almost 850 degrees (17–888 K) with relative thermal sensitivity up to 3.5 %/K at 405 K. Additionally, an impressive value of S r = 1.17 %/K at elevated temperature (738 K) was obtained. Temperature sensing was possible by utilizing both Pr3+ and Tb3+ emissions, showing different thermal quenching properties. That was key for broadening the temperature operating range compared to the singly-doped Y 2 SiO 5 :Pr3+ phosphors. [Display omitted] • Co-substitution of inorganic host structure to broaden temperature operating range. • Y 2 SiO 5 :Pr, Tb as a highly efficient and sensitive luminescence thermometer in the 17–888 K range. • Multiphonon relaxation utilized as a tool to extend the operating range of the luminescence thermometer. [ABSTRACT FROM AUTHOR]

Abstract X-ray induced effects in LuPO 4 :Eu3+ sintered thermoluminescent material were investigated by absorption and photoluminescence measurements between 20 and 300 K. Evidence for Eu3+→Eu2+ conversion upon exposure to X-rays was obtained as narrow band blue Eu2+ photoluminescence was observed. The low temperature luminescence of Eu2+ ions in X-rayed LuPO 4 :Eu ceramics showed a unique fine structure with a sharp zero-phonon line at 425.8 nm and well-resolved vibronic structure. Excitation spectra of the Eu2+ luminescence revealed a rich structure in which individual 4f7→ 4f6(7F J)5d1 zero-phonon lines accompanied by vibronic transitions were identified. A detailed analysis allowed an accurate calculation of the Eu3+-like 4 f6(7F J) core levels in the 4 f65d1 excited configuration. The 4f6 core splitting is different from that of the 7F J states for Eu3+ in LuPO 4 , providing evidence for the role of 4f6–5d interaction on the splitting of the 4f6 configuration. The unique luminescence of Eu2+ with a small Stokes shift and well-determined energies of 4f6(7F J)5d1 excited states make LuPO 4 :Eu a model system for testing theoretical models which are presently developed to calculate and predict the energy level structure and Stokes shift of 4fn–4fn−15d1 transitions of lanthanides. [ABSTRACT FROM AUTHOR]

Photoluminescence of Ce 3+ - and Pr 3+ -activated Sr 2 GeO 4 powders was measured between 17 and 600 K. For both ions strong 4f n−1 5d n →4f n (d-f) emission is observed at low temperatures, around 410 nm (Ce 3+ ) and 280 nm (Pr 3+ ). The Ce 3+ d-f emission quenches starting at 150 K and disappearing completely just above room temperature. Pr 3+ d-f luminescence shows an onset of quenching also around 150 K and disappears completely between 250 and 300 K. For Pr 3+ quenching of the d-f emission was connected with an increasing intensity of the 3 P 0 luminescence at first and 1 D 2 emission at even higher temperatures. Both these 4f n →4f n emissions were observed up to 600 K. Based on the similar quenching temperatures, thermally stimulated photoionization of the 5d electrons from 5d level of Ce 3+ or Pr 3+ to the conduction band is proposed as the most probable mechanism for quenching of the d-f emissions. [ABSTRACT FROM AUTHOR]

Abstract: In this study, it is shown how the temperature range of luminescent thermometers can be widened in an unprecedented way by combining the intra‐ and interconfigurational transitions of the Pr3+ ion in a single material. Using Sr2GeO4:Pr3+ crystalline powders as an illustrative example, the implementation of luminescence thermometry is reported in the broadest temperature range up to now (17–600 K) with a remarkable performance: maximum relative sensitivity values of 9.0% · K−1 (at 22 K, cryogenic range), 0.6% · K−1 (at 300 K, physiological range), and 0.5% · K−1 (at 600 K, high‐temperature range) and minimum temperature uncertainty of 0.1 K. [ABSTRACT FROM AUTHOR]

Photophysical and optical properties of 4-(4'-(diphenylamino)benzylidene)-2-phenyloxazol-5(4 H)-ones differing in the peripheral substituent have been investigated in chloroform, solvent mixture, polymer matrix and solid state. These properties are influenced by the nature of the substituent on the phenyl ring and the environment. The dye bearing phenyl group or without substituent in para position of the phenyl group in 2-phenyloxazol-5(4 H)-one moiety has the brightest emission in a solid state, whereas the dye with cyano functional group possesses the strongest emission in chloroform. The spectral behavior of the tested dyes is dependent on the solvent mixture. The fluorescence of the oxazolone dye in CHCl 3 /MeOH was reduced due to hydrogen bond formation, whereas addition of water to the THF or DMSO indicate the enhancement in emission caused by aggregation induced emission (AIE). The absorption and fluorescence spectra of the oxazolone polymer thin film are shifted to blue compared to the dyes dissolved in chloroform. The surface topography of the oxazolone thin films was examined using atomic force microscopy (AFM). The optical properties of the dye layers and dyes immobilized in PMMA matrix were determined by spectroscopic ellipsometry (SE). The absorption coefficient, refractive index, extinction coefficient and the energy bandgap can be effectively manipulated by changing substituent in the dye structure. [Display omitted] • Photophysical and optical properties of oxazolone derivatives were investigated in solution, polymer matrix and solid state. • Spectroscopic properties of the dyes can be tuned by the substituent effect. • Oxazolones show solid-state emission in orange and red regions. • Oxazolones demonstrated AIE due to restricted intramolecular motion mechanisms. • Atomic force and spectroscopic ellipsometry techniques were performed for oxazolone thin films. [ABSTRACT FROM AUTHOR]

Ceramics of Lu 2 O 3 activated with either Tb 3+ or Pr 3+ and co-doped with one of the transition metal ions – Ti, Hf or Nb – were investigated for their energy storage properties. Photoluminescence, thermoluminescence (TL) and optically stimulated luminescence spectra were recorded and discussed together with thermoluminescent glow curves. The Pr 3+ and Tb 3+ ions constitute luminescent centers and participate in the energy storage. However, as the thermoluminescence glow curves showed, the Ti, Hf and Nb co-dopants have a significant impact on glow curve pattern, in particular on the temperature at which the maximum thermoluminescence occurred. For the Tb,Ti and Pr,Ti as well as for the Pr,Nb one main TL peak appeared around 360–370 °C. For other compositions it varied from 210 °C for Tb,Nb, through 230 °C for Tb,Hf to 250 °C for Pr,Hf. In either case additional TL components of lower intensities were observed. They spread over 50–450 °C. The TL data led to the conclusion that the co-dopant – a necessary component to induce a significant energy storage capacity in the materials – may not be directly involved in trapping the excited carriers. Instead, it may rather generate other point defects which, individually or as clusters, would do the work. Energy storage was found to be connected with an appearance of an induced excitation/absorption band spreading over around 350–500 nm and peaking near 400 nm. A prolonged stimulation into this band caused green (for Tb-series) or red (for Pr-series) optically stimulated emission. Such a stimulation allows entirely bleaching out the induced absorption. The optically stimulated luminescence for all members of the Tb-series led to luminescence from both C 2 and C 3i sites offered by the host lattice. All compositions of the Pr-series produced optically stimulated emissions upon 400 nm radiation only by means of the Pr 3+ occupying the C 2 site. [ABSTRACT FROM AUTHOR]

Radio- and thermoluminescent properties of HfO 2 :Ti sintered ceramics were investigated in the temperature range of 10–300 K. Fabrication atmosphere altered somewhat the efficiency of radioluminescence but did not affect the spectral distribution of the broad scintillation band covering the 380–570 nm range of wavelengths and peaking at 522 nm at 10 K and about 490 nm at 300 K. The analogous shift was seen in photoluminescence. Scintillation efficiency was continuously growing from 10 K to 300 K, while photoluminescence intensity was stable in the 10–250 K range of temperatures and was reduced by about 30% at 300 K. Analysis of these observations allowed to conclude that diffusion of carriers generated upon the impact of high-energy photons towards the Ti emitting center is strongly temperature-dependent and inferior at lower temperatures. Upon exposure to X-rays at 10 K the ceramics stored more than 50% of the absorbed energy. This energy could be recovered later upon thermal stimulation of the ceramics. Four main thermoluminescent peaks were then produced at 95, 140, 243 and 278 K. This effect was tentatively associated with theoretically predicted self-trapping of holes in HfO 2 . The so-called partial cleaning and T max –T stop experiments indicated that some fraction of traps shows a continuous distribution of their depths. [ABSTRACT FROM AUTHOR]

The studies presented in this paper were devoted to optimizing the synthesis conditions of nanoscale YPO 4 doped with optically active lanthanide ions (Eu 3+ ). In frame of this work the structural, morphological and spectroscopic investigation of the fabricated powders were performed. The materials were synthesized in phosphate ionic liquid as precipitating and morphology controlling agent of the resulting powders. Influence of the synthesis conditions such as: pH of the solution and its quantitative composition, temperature and time of the synthesis, and the post-fabrication heat-treatment temperature – on the phosphors optical properties and morphology of the particles was investigated. The achieved results showed the significant role of the IL (ionic liquid) in the synthesis procedure, in consequence leading to obtained pure luminescent materials with very good optical properties as long decay time and high quantum efficiency. [ABSTRACT FROM AUTHOR]

[Display omitted] • Narrowing of the half-width of the fluorescence band as compared to the half-width of the absorption band. • Large Stokes shift which is solvent dependent. • Fast response of the dyes to changes in pH. • Tribranched chromophore exhibit a large σ 2 eff value. • Formation of the inclusion complexes with β-CD, which results in enhanced fluorescence. A common motif in the design of organic dye compounds is that of an electron donor and an acceptor moiety linked through a conjugated bridge, but more complicated structures can also be built using such motifs as building blocks. Following these principles, we synthesized two styrylpyridinium dyes, a linear one and a branched molecule composed of three units of the mono moiety connected by benzyl group and investigated their photophysical properties in different environments: their linear absorption, one-photon excited fluorescence and two-photon absorption properties. The compound with the symmetrically substituted phenyl core shows a redshift of the absorption and fluorescence bands. Spectrally resolved two-photon absorption cross section measurements carried out by femtosecond Z-scan technique show that the value for the trimer is over twelve times larger than that for the monomer, and not just three times as expected from the molar mass increase. Large two-photon absorption (2PA) values were measured in the near infrared (NIR) region. The prototropic study indicates that the protonation of the amino group blocks a lone pair on the nitrogen atom, making the photoinduced electron transfer process from the amine group to the pyridinium ring ineffective. This results in the reduction of the long-wavelength absorption with a simultaneous increase of the band in the short-wavelength region of the spectrum and a decrease in the fluorescence intensity. The behavior of dyes in the presence of β-cyclodextrin was also studied based on NMR, UV–Vis, and fluorescence spectroscopy. The performed experiments indicated the formation of 1:1 inclusion complex in aqueous solution. [ABSTRACT FROM AUTHOR]

Accurate, fast, and non-invasive methods for the determination of the local pressure magnitude are crucial for the investigation of the physical and chemical behavior of materials at the extreme conditions of high pressure. A promising method for remote operando pressure measurements is luminescence manometry. However, a limiting bottleneck for high-pressure readout is the usually occurring quenching of the emission signal of the luminescent sensor material upon compression. In this work, we reported for the first time the pressure-induced intensity enhancement (by 3 orders of magnitude) of the 4f7(6P 7/2)→4f7 (8S 7/2) emission line of Eu2+ in the UV range due to pressure-induced configurational crossover between the excited 4f65d1 and 4f7 energy levels in SrB 4 O 7 host. The peak centroid of the narrow 4f7 → 4f7 transition exhibits a significant red-shift (∼ -12.84 cm−1 GPa−1; 0.17 nm GPa−1) with simultaneous temperature independence of the line position (4.8·10−4 nm K−1). The pressure sensitivity of the proposed system is competitive to the so far well-established luminescent pressure sensors based on Al 2 O 3 :Cr3+ (ruby) and SrB 4 O 7 :Sm2+ with characteristic narrow line emission in the red range, and offers an alternative spectral range in parallel with an intensity enhancement at higher pressures. This novel pressure gauge may significantly improve the accuracy of the remote pressure measurements and open up new horizons for materials science research at even higher pressures. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Persistent luminescence phosphors, Tb3+, Sr2+ co-doped Lu2O3 ceramics were fabricated under vacuum at 1870°C. A strong green color afterglow could be observed after excitation with 254nm UV radiation. The afterglow was found to be roughly doubled in intensity upon stimulation with violet or blue-green photons (∼400–600nm) as well as upon IR radiation (∼800–980nm). Hence, the enhancement of the green afterglow could also be attained by means of natural sunlight. Short wavelength UV radiation was found to induce an extrinsic absorption band below about 600nm and extending into the deep UV. This was mirrored by a simultaneous decrease of the absorption by Tb3+ around 230–320nm. The extrinsic absorption seemed to contain at least two overlapping components which supposedly resulted from a band related to Tb4+/Tb3+-h and a feature resulting from F/F+ centers created upon irradiation with short UV. This absorption was shown to be reversible, as it disappeared after a short heat treatment at about 300°C as well as with continuous irradiation of ∼400nm radiation. [Copyright &y& Elsevier]

Abstract: Lutetium and yttrium oxides are promising scintillating materials suitable for use in medical planar X-ray imaging and mammography. In this paper the procedure for preparation of europium doped mixed lutetium–yttrium oxide nanopowders using polymer complex solution synthesis method is presented. Detailed information on nanopowder phase, morphology and crystallinity are obtained using X-ray powder diffraction, SEM and TEM while optical properties are investigated by photoluminescence and radioluminescence measurements. Constituting nanoparticles are 20–40nm in size, and have excellent structural ordering in cubic bixbyite-type. Unit cell parameter, ionic coordinates, crystal coherence size and microstrain are determined from Rietveld analysis. All powders show strong Eu3+-characteristic red emission, with an average 5D0 emission lifetime of 1.5ms. Radioluminescence efficiency is about 15% of the commercial micron-sized Gd2O2S:Eu3+ powder while negligible level of afterglow is found. [ABSTRACT FROM AUTHOR]

Using luminescent materials for temperature measuring is considered the perspective remote technique nowadays. Designing new materials which combine a wide operating range with satisfying relative thermal sensitivity (S r) and temperature uncertainty values is still a challenge. In this paper, we study the luminescence properties and thermometric performance of a mixture of two phosphors. These are Ga-modified garnets - Y 3 (Al 3 Ga 2)O 12 :0.1%Pr and Y 3 (Al 1 Ga 4)O 12 :0.1%Pr - already reported as dual-mode luminescent thermometers. We show a new concept to improve important thermometric parameters of luminescence thermometers. We prove that such a mixture offers a significantly flatter course of the relative thermal sensitivity vs. temperature with S r around 1%K−1 over a broad temperature interval. Independently of which of the thermometric parameter is used, temperature measurement may be easily executed in the broad range of temperatures, 15–675 K. At the core of our concept is the use of two phosphors of the same crystal structure. This allows for the equally effective excitation of the two components of the mixture, while both use the same activator. [Display omitted] • Dual-mode thermometry is executed over 15–675 K range mixing two phosphors. • The Mixed phosphors belong to the same crystal structure of Pr activated garnets. • The same crystal structure allowed efficient excitation with the same energy. • The Mixed phosphors allowed to improve the accuracy of temperature measuring. [ABSTRACT FROM AUTHOR]

• Dual-mode thermometry is executed in YAG:Pr3+-YGG:Pr3+ systems. • Bandgap engineering allows enhancing the performance of the thermometers. • YAG:Pr-YGG:Pr present manageable high relative sensitivity and high accuracy. • Garnet-based luminescence thermometers work effectively in the range 17–700 K. • Relative temperature errors are calculated and compared for all the garnets. The temperature determination using luminescent materials is nowadays considered the perspective remote technique for temperature gauging, despite the few examples reported so far combining wide operating temperature range with satisfying relative thermal sensitivity and temperature uncertainty values. In this paper, we study the Y 3 (Al,Ga) 5 O 12 :0.1%Pr phosphors with controlled Ga:Al composition to deliberately affect their luminescent properties. We demonstrate that the energy barrier for thermal quenching of the 5d-4f luminescence can be effectively tailored, yielding the fine tune of the thermometric parameters of these phosphors. By exploiting time-resolved and time-integrated approaches we show that the thermometers can cover the 17–700 K temperature range with a maximum relative sensitivity up to 3.6%·K−1 and a temperature uncertainty as lower as 0.02 K. For each sample, the temperature readout of the distinct thermometric parameters is compared illustrating that the performance of the thermometers should also consider the relative temperature error between the calculated and the measured temperatures, besides relative thermal sensitivity and temperature uncertainty. [ABSTRACT FROM AUTHOR]

The efficient 4f65d→4f7 (d-f) luminescence from Eu2+ is well-known for host lattices where Eu2+ is substituted on a divalent (e.g. Ca2+, Sr2+) or monovalent (e.g. Na+, K+) cation site. Only recently some studies appeared concerning d-f emission from Eu2+ on a trivalent cation site. The stable Eu2+ emission was observed in X-ray irradiated LuPO 4 :Eu3+ crystals where Eu2+ is produced through trapping of conduction band electrons generated by X-ray absorption. Here, we demonstrated that Eu2+ can also be chemically stabilized in YPO 4 and LuPO 4 through co-doping with a tetravalent charge compensator: Hf4+. In orthophosphate crystals doubly doped with Eu and Hf, the characteristic Eu2+ emission is observed at low temperatures without the need for X-ray irradiation. The excitation and emission spectra show strong and narrow zero-phonon lines and a rich vibronic structure. In the excitation spectra a multitude of zero-phonon transitions to individual crystal field components of 7F J multiplets in the 4f6(7F J)5d excited state was observed for Eu2+ in both LuPO 4 and YPO 4. Analysis of the spectra is consistent with a slightly larger crystal field splitting for Eu2+ on the smaller Lu3+ site (compared to Y3+). The observation of many 4f6(7F J)5d electronic origins make these systems to be model compounds for testing the validity of theoretical models for energy level calculations of 4f65d states of Eu2+. Image 1 • Stable Eu2+ ions in LuPO 4 and YPO 4 single crystals were obtained by co-doping with Hf4+. • Peculiar luminescence and excitation of Y/LuPO 4 :Eu2+,Hf4+ explained. • Core Eu3+-like levels of 4f6(7F J)5d excited state are seen in excitation spectra. [ABSTRACT FROM AUTHOR]