Single-Crystal Red Phosphors and Their Core-Shell Structure for Improved Water-Resistance for Laser Diodes Applications.

A solvent-vapor transport route produces centimeter-sized single-crystal red phosphors. The epitaxial growth route to yield its core-shell structure at ambient temperature was adopted. These red phosphors could be applied in all-inorganic WLED devices. Cs2 TiF6 :Mn4+ (CTFM) single crystal provides enhancement of quantum efficiency, moisture resistance, and thermal stability compared to polycrystalline powders. The internal quantum efficiency can reach as high as 98.7 %. To further improve waterproof stability, the Cs2 TiF6 (CTF) shell with tunable thickness has been epitaxially grown on the CTFM single crystal surface and a unique three-step photoluminescence intensity evolution mechanism has been proposed. By combining as-prepared CTFM@CTF core-shell structured single crystal, YAG:Ce single crystal and blue-chip, warm WLEDs with excellent color rendition (Ra =90, R9 =94), low correlated color temperature (CCT=3155 K), and high luminous efficacy were fabricated without any organic resins.

Changes of Color and Fluorescence of Resin Composites Immersed in Beer.

OBJECTIVE: The aim of this study was to evaluate changes of color and fluorescence of resin based composite exposed to beer. MATERIALS AND METHODS: 84 samples (13 mm in diameter and 1.5 mm thick) of microhybrid composite Gradia DirectTM extra bleach white were immersed in 5 different beers (dark and light) or distilled water. Color and fluorescence were measured prior and after 1-, 7-, and 14-day immersion by Spectrophotometer Thermo Evolution 600 and Fluorolog-3-221 spectrofluorometer. RESULTS: Resin based composites changed color after immersion in beers of different types. Beers with higher optical absorption induced greater color changes. The fluorescence intensity of composites was decreased after immersion in beer, but the shape of fluorescence spectra was not changed. 14-day immersion in Bernard dark beer caused the greatest changes in optical properties of composite: ΔE*=9.0 and 57.6% reduced fluorescence. CONCLUSION: Dark and light beers changed optical properties of resin based composite. The color change come exclusively from the change of chroma. CLINICAL SIGNIFICANCE: To fully meet esthetic criteria when using dental materials in restoration it is crucial to match optical properties of teeth and dental restoration at the moment of placement, but also to keep the match over the time. Considering that staining in beer causes changes in color and fluorescence of composites and that discoloration is a frequent reason for replacement of composite restorations, the data and conclusions on discoloration of dental restorations caused by beer consumption should aid dental professionals when reaching for high esthetics of modern dentistry.(J Esthet Restor Dent 28:330-338, 2016).

Organic solvent-assisted co-precipitation synthesis of red-emitting K2TiF6:Mn phosphors with improved quantum efficiency and optimized morphology.

We report an organic solvent-assisted (OSA) co-precipitation strategy for the production of Mn4+-activated K2TiF6 phosphor. The phosphor particle size was controlled through the selection of organic solvents with an alcohol functional group and different carbon chain lengths used in the synthesis. The synergistic effect of the organic solvent and hydrofluoric acid results in large smoothed hexagonal-shaped crystal sheets of particles that become larger as the carbon chain length of the organic solvent increases. The photoluminescence (PL) properties of K2TiF6:Mn powders strongly depend on the size and thickness of the particles. The addition of n-butanol during the synthesis increases the emission intensity of K2TiF6:Mn by 208%. The PL quantum efficiency of phosphors prepared using the n-butanol-assisted strategy is much higher (98.2%) than that of conventionally prepared phosphors (89.9%). Our findings demonstrate a way to prepare the K2TiF6:Mn phosphor with targeted morphology and very high quantum efficiency and also provide the route for the optimization of all Mn4+-activated fluoride phosphors used in white light-emitting diodes.

Hydrothermal Synthesis and Properties of Yb3+/Tm3+ Doped Sr2LaF7 Upconversion Nanoparticles.

We report the procedure for hydrothermal synthesis of ultrasmall Yb3+/Tm3+ co-doped Sr2LaF7 (SLF) upconversion phosphors. These phosphors were synthesized by varying the concentrations of Yb3+ (x = 10, 15, 20, and 25 mol%) and Tm3+ (y = 0.75, 1, 2, and 3 mol%) with the aim to analyze their emissions in the near IR spectral range. According to the detailed structural analysis, Yb3+ and Tm3+ occupy the La3+ sites in the SLF host. The addition of Yb3+/Tm3+ ions has a huge impact on the lattice constant, particle size, and PL emission properties of the synthesized SLF nanophosphor. The results show that the optimal dopant concentrations for upconversion luminescence of Yb3+/Tm3+ co-doped SLF are 20 mol% Yb3+ and 1 mol% Tm3+ with EDTA as the chelating agent. Under 980 nm light excitation, a strong upconversion emission of Tm3+ ions around 800 nm was achieved. In addition, the experimental photoluminescence lifetime of Tm3+ emission in the SLF host is reported. This study discovered that efficient near IR emission from ultrasmall Yb3+/Tm3+ co-doped SLF phosphors may have potential applications in the fields of fluorescent labels in bioimaging and security applications.

Characterization of cereal flours by fluorescence spectroscopy coupled with PARAFAC.

This paper presents parallel factor analysis (PARAFAC) of fluorescence of cereal flours. Excitation-emission matrices (EEM's) of different cereal flours (wheat, corn, rye, rice, oat, spelt, barley and buckwheat) were measured in a front-face configuration over the ultraviolet-visible spectral range. EEM's showed that flours strongly fluoresce in two spectral regions, where amino acids, tocopherols, pyridoxine and 4-aminobenzoic acid show intense emissions. 4-component PARAFAC was used to model flour fluorescence and to decompose EEM's into excitation and emission spectra of each component. PARAFAC also provided relative concentrations of these components. The largest differences between flours were found in the concentration levels of the first and third component. Finally, variations in concentrations of PARAFAC modelled components were analysed in relation to the botanical origin of flour samples.

Genetic Polymorphisms of Catechol-O-Methyltransferase: Association with Temporomandibular Disorders and Postoperative Pain.

AIMS: To evaluate the association between catechol-O-methyltransferase (COMT) gene polymorphisms and temporomandibular disorders (TMD), TMD pain, psychosocial impairment related to TMD, and postoperative pain. METHODS: A total of 90 patients with a diagnosis of painful TMD and 92 matched controls were investigated for the presence of TMD, TMD pain, and psychosocial variables by the Research Diagnostic Criteria for TMD. In a prospective cohort study of 40 subjects who underwent extraction of at least one fully impacted mandibular third molar, subjects had 6 months post-surgery follow-up of postoperative pain. DNA extracted from peripheral blood was genotyped for three COMT polymorphisms (rs4680, rs6269, and rs165774) by real-time TaqMan method. The association between COMT polymorphisms and clinical variables was determined by calculating odds ratios (OR) and their 95% confidence intervals (CI). RESULTS: Homozygous AA genotype and heterozygous variant A allele carriers (genotype AG/AA) for rs165774 polymorphism were associated with increased risk of TMD compared to wild type (wt) GG genotype (OR = 9.448, P = .006; OR = 2.088, P = .017, respectively). In addition, AA genotype was associated with increased risk of arthralgia (OR = 4.448, P = .011), myofascial pain (OR = 3.543, P = .035), and chronic TMD pain (OR = 6.173, P = .006), compared to wt genotype. AA genotype for rs6269 polymorphism was related to less postoperative chronic TMD pain (P = .025) and lower postoperative acute pain at the extraction site (P = .030). No associations with depression and somatization were observed. CONCLUSION: AA genotype of rs165774 could be a significant risk factor for the development of TMD and TMD pain, while AA genotype of rs6269 presents less postoperative chronic TMD pain and acute pain at a dental extraction site.