White- and blue-light-emitting dysprosium(III) and terbium(III)-doped gadolinium titanate phosphors.

Here we report the synthesis and structural, morphological, and photoluminescence analysis of white- and blue-light-emitting Dy3+ - and Tm3+ -doped Gd2 Ti2 O7 nanophosphors. Single-phase cubic Gd2 Ti2 O7 nanopowders consist of compact, dense aggregates of nanoparticles with an average size of ~25 nm for Dy3+ -doped and ~50 nm for Tm3+ -doped samples. The photoluminescence results indicated that ultraviolet (UV) light excitation of the Dy3+ -doped sample resulted in direct generation of white light, while a dominant yellow emission was obtained under blue-light excitation. Intense blue light was obtained for Tm3+ -doped Gd2 Ti2 O7 under UV excitation suggesting that this material could be used as a blue phosphor.

Self-referenced luminescence thermometry with Sm(3+) doped TiO2 nanoparticles.

The performance of Sm(3+) doped TiO2 nanoparticles for luminescence temperature sensing was tested over a temperature range from room to 110 °C. The Sm(3+) ions were incorporated into TiO2 nanocrystals using hydrolytic sol-gel route. Microstructural characterization of the obtained material was performed using transmission electron microscopy and x-ray diffraction measurements. Luminescence emission spectra of Sm(3+) doped TiO2 nanoparticles consists of two distinct spectral regions: the high energy region associated with the trap emission of the TiO2 host, and the low energy region with well-resolved emission peaks of the Sm(3+) ions. The ratio between Sm(3+) emission and TiO2 trap emission shows strong temperature dependence, and is tested for temperature sensing. The relative sensor sensitivity was found to be higher than 1% °C(-1) over given temperature range with the maximum value of 10.54% °C(-1) at 57.5 °C. Lifetime data derived from the Sm(3+) emission decay revealed that time-resolved measurements provide comparable quality of temperature sensing as corresponding ratiometric measurements, with a maximum relative sensitivity of 10.14% °C(-1) at 66.5 °C.

Temperature sensing from the emission rise times of Eu(3+) in SrY2O4.

The emission rise time of Eu(3+)-doped SrY2O4 was investigated in the temperature range of 20-200 °C for application in luminescence thermometry. After pulsed excitation, the energy transfer between the adjacent Eu(3+) ions causes a emission build-up from the (5)D0 level of Eu(3+) and a notable emission rise occurs prior to decay. The emission rise-time values linearly decrease with temperature, providing an absolute sensitivity of 0.66 µs °C(-1) and a maximal relative sensitivity of 5.53% °C(-1) at 200 °C, for samples containing 0.5 at% Eu(3+) ions. It is shown that the time after excitation at which emission reaches a maximum (time-to-max) can also be exploited for temperature sensing, since it is easily measurable and shows a linear dependence with temperature.

Understanding the power of luminescence ratiometric thermal history indicators driven by phase transitions: the case of Eu3+ doped LaVO4.

Finding thermal history phosphors with high sensitivity and a consistent readout is required for reliable thermal history determination with high temperature resolution. This work presents a new thermal history phosphor based on the luminescence of Eu3+ ions in LaVO4 to meet these requirements. As demonstrated, raising the annealing temperature causes a structural phase transition from a low-temperature tetragonal phase to a high-temperature single-stranded phase. The associated change in the local point symmetry of the crystallographic site occupied by Eu3+ ions result in a significant decrease in the emission intensity ratio of the 5D0 → 7F2 band relative to the 5D0 → 7F1 band, which enables the development of the ratiometric thermal history phosphor with the relative sensitivity of 0.38% °C-1 at 800 °C. Its applicative potential for thermal history readout was proved in the proof-of-concept experiment.

A novel method for the functionalization of gamma-irradiated single wall carbon nanotubes with DNA.

In this work we describe a novel method for highly efficient functionalization of single wall carbon nanotubes (SWCNTs) by DNA wrapping. Exposure of SWCNTs to gamma-irradiation (50 kGy) has lowered by one order of magnitude the amount of single stranded deoxyribonucleic acid (ssDNA) required for SWCNT modification. The resulting hybrids of gamma-irradiated SWCNTs and ssDNA were characterized by optical absorbance spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. Atomic force microscopy was used to investigate the morphology of hybrids. While gamma-irradiation in three different media has significantly improved the process of SWCNT dispersion, irradiation in ammonia was the most efficient. The gamma-irradiated SWCNTs functionalized with ssDNA were stabilized by electrostatic forces. This preliminary study suggests that gamma-irradiation can significantly improve the functionalization of SWCNTs with DNA.

Evaluation of Staining-Dependent Colour Changes in Resin Composites Using Principal Component Analysis.

Colour changes in Gradia Direct™ composite after immersion in tea, coffee, red wine, Coca-Cola, Colgate mouthwash, and distilled water were evaluated using principal component analysis (PCA) and the CIELAB colour coordinates. The reflection spectra of the composites were used as input data for the PCA. The output data (scores and loadings) provided information about the magnitude and origin of the surface reflection changes after exposure to the staining solutions. The reflection spectra of the stained samples generally exhibited lower reflection in the blue spectral range, which was manifested in the lower content of the blue shade for the samples. Both analyses demonstrated the high staining abilities of tea, coffee, and red wine, which produced total colour changes of 4.31, 6.61, and 6.22, respectively, according to the CIELAB analysis. PCA revealed subtle changes in the reflection spectra of composites immersed in Coca-Cola, demonstrating Coca-Cola's ability to stain the composite to a small degree.

Hydrothermal synthesis and nanostructure of carbonated calcium hydroxyapatite.

The influence of precursor concentration, pressure, temperature and time of hydrothermal synthesis on the development of calcium hydroxyapatite structure has been analyzed. The obtained results show that it is possible to adjust the conditions of hydrothermal synthesis from solutions of relatively high concentrations to obtain calcium hydroxyapatite nanopowders of well-defined structure. The relationship between the synthesis and the lattice parameters, as well as the crystallite size and the microstructure of synthesized hydroxyapatite has been established. The synthesized powders are preferentially carbonated hydroxyapatite of the B type in the form of agglomerates that accommodate two-modal size pores of 1.5-10 and 50-200 nm. The structure of calcium hydroxyapatite particles consists of crystallites 8-22 nm in size, bound within prime particles, which size is between 10 and 63 nm, that in turn form bigger agglomerates 200 nm in size, which further cluster building up agglomerates 5-20 microm in size.

Photoacoustic measurement of internal quantum efficiency and observation of the exciton effect in GaSe with photoacoustic phase spectra.

We studied the room temperature photoacoustic spectra of GaSe single crystals in the vicinity of the energy gap. Exciton formation was observed in both amplitude and phase spectra. The thermal source that arises in the illuminated sample because of optical absorption without free-carrier generation was incorporated in the heat diffusion equation in order to extend the theoretical approach of photoacoustic signal generation. We calculated the optical absorption coefficient, which shows the exciton formation, and the electron-hole generation quantum efficiency eta(G) using an extended model from the phase and amplitude photoacoustic spectra, respectively.

In vivo monitoring of chlorophyll fluorescence response to low-dose gamma-irradiation in pumpkin (cucurbita pepo) leaves.

The effect of gamma-irradiation on the in vivo-measured chlorophyll fluorescence in a pumpkin leaves (Cucurbita pepo) has been investigated. Plants were grown in the same environment, then divided into several groups and irradiated at ambient conditions at small dose levels (up to 13.4 Gy) with (60)Co gamma-rays. The post-irradiation effect on chlorophyll status in the leaves was examined by measuring chlorophyll fluorescence 2 days (48 h) after exposure. It is undoubtedly found that the value of fluorescence intensity ratio (FIR) at 690 nm and 735 nm (F(690)/F(735)) depends upon the ionizing radiation dose. Even with the smallest dose of 3.35 Gy, ionizing radiation notably altered the fluorescence spectra of leaves. The spectra difference was manifested by decrease of FIR due to changed chlorophyll luminescence, the possible reason for which could be increase of chlorophyll concentration during the recovery process of the plant. The potential implications of these results for plant physiological status monitoring, as well as for pollution detection and assessment, are discussed in brief.