SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Garnet

168

This work presents a novel white light device. An yttrium aluminum garnet (YAG) phosphor-incorporated zinc oxide (ZnO) film is deposited on a slide glass substrate by ultrasonic spray pyrolysis. A nanoflower consisting of a hexagonal nanopetal is formed on the surfaces of the samples, and the sizes of the nanopetal are approximately 200 to 700 nm. Additionally, the nanopetal becomes blunted with an increasing incorporated amount of YAG. As the incorporated amount is 1.5 and 2.5 wt.%, the photoluminescence color of the YAG-incorporated ZnO film is nearly white, possibly contributing to the YAG emission and the band-to-deep level transition in the ZnO film.

Concepts: Aluminium, Zinc, Color, Titanium dioxide, Zinc oxide, Yttrium aluminium garnet, Garnet, Yttrium

31

The physics of strong-field applications requires driver laser pulses that are both energetic and extremely short. Whereas optical amplifiers, laser and parametric, boost the energy, their gain bandwidth restricts the attainable pulse duration, requiring additional nonlinear spectral broadening to enable few or even single cycle compression and a corresponding peak power increase. Here we demonstrate, in the mid-infrared wavelength range that is important for scaling the ponderomotive energy in strong-field interactions, a simple energy-efficient and scalable soliton-like pulse compression in a mm-long yttrium aluminium garnet crystal with no additional dispersion management. Sub-three-cycle pulses with >0.44 TW peak power are compressed and extracted before the onset of modulation instability and multiple filamentation as a result of a favourable interplay between strong anomalous dispersion and optical nonlinearity around the wavelength of 3.9 μm. As a manifestation of the increased peak power, we show the evidence of mid-infrared pulse filamentation in atmospheric air.

Concepts: Fundamental physics concepts, Physics, Light, Electromagnetic radiation, Laser, Frequency, Yttrium aluminium garnet, Garnet

28

BACKGROUND: The efficacy of fractional erbium-doped yttrium aluminum garnet (Er:YAG) and carbon dioxide (CO(2) ) lasers are well substantiated. OBJECTIVE: To compare the efficacy and safety of these two laser systems for treatment of atrophic scars in dark-skinned patients. MATERIALS AND METHODS: Twenty-four subjects with acne scars were randomly treated with a fractional Er:YAG laser on one side and a fractional CO(2) laser on the other side. All subjects received two treatments with a 2-month interval. Objective and subjective assessments were obtained at baseline and 1, 3, and 6 months after the final treatment. RESULTS: At the 6 month follow up, 55% and 65% of Er: YAG and CO(2) laser sites, respectively, were graded as having more than 50% improvement of scars. Improvement progressed significantly from 1- to 6-month follow-up (p < .001). There was no significant difference in clinical improvement between the two systems at 1- (p = .90), 3- (p = .54), and 6-month (p = .87) follow-up. Reduction in scar volume corresponded to clinical evaluation. CONCLUSIONS: Fractional Er:YAG and CO(2) lasers provided comparable outcomes of scar treatment, but fractional CO(2) laser was associated with greater treatment discomfort.

Concepts: Carbon dioxide, Scar, Acne vulgaris, Erbium, Yttrium aluminium garnet, Garnet, Solid-state laser, Active laser medium

27

BACKGROUND: Tranexamic acid (TA) has recently gained in popularity in the treatment of pigmentary disorders. OBJECTIVE: To evaluate the clinical efficacy and safety of oral TA combined with low-fluence 1064-nm quality-switched neodymium-doped yttrium aluminum garnet (QSNY) laser for the treatment of melasma. MATERIALS AND METHODS: Forty-eight patients with melasma were enrolled in the study and subsequently divided into two groups: a combination group and a laser treatment group. All patients were treated with two sessions of low-fluence QSNY laser, and patients in the combination group took 8 weeks of oral TA. Two blinded dermatologists evaluated patients using the Modified Melasma Area and Severity Index (mMASI) and a clinical improvement scale. RESULTS: Mean mMASI score 4 weeks after the second treatment decreased significantly in both groups from base line. Based on overall clinical improvement, a greater number of patients scored as grade 3 and more in the combination group; no patients were scored as grade 4 in the laser-alone group. CONCLUSIONS: Oral TA may prove a safe and efficient treatment option for melasma in combination with low-fluence QSNY laser therapy.

Concepts: Medicine, Aluminium, Dye laser, Erbium, Yttrium aluminium garnet, Garnet, Laser hair removal

26

A study was designed to determine and describe the changes induced in the anterior segment of the eye and the intraocular pressure (IOP) after laser peripheral iridotomy (LPI) versus phacoemulsification in primary angle closure suspects (PACS) and primary angle closure (PAC).

Concepts: Ophthalmology, Yttrium aluminium garnet, Garnet, Yttrium

26

Ab initio embedded cluster calculations on Ce(3+)-doped Y3Al5O12, Lu3Al5O12, Gd3Al5O12, Y3Ga5O12, Lu3Ga5O12, and Gd3Ga5O12, which do not make use of any adjustable parameter, support recent assignments of the seventh 4f level of Ce(3+) in garnets [Przybylińska et al., Appl. Phys. Lett., 2013, 102, 241112] and that the splitting of the 4f shell of Ce(3+) in these materials is slightly smaller than 4000 cm(-1) and much larger than the 2000-2500 cm(-1) commonly assumed in analyses of 5d → 4f emission bands. Why this wrong assumption has been working well so far is explained by the fact that the intensity of the emission to the seventh level of the 4f(1) configuration is found to be only one hundredth of the integrated intensity of the emissions to the other six levels, which group themselves into two sets of three individual levels separated by 2000-2500 cm(-1). The effective field splitting and the spin-orbit coupling splitting are found to be of the same size. From a strong field coupling point of view, the first six levels result from the interactions between (2)T2u and (2)T1u cubic levels and the higher, isolated seventh level comes directly from the cubic (2)A2u. From a weak field coupling point of view, the first three levels result from the splitting of (2)F5/2, the second three levels from the splitting of (2)F7/2 and the seventh level from a strong, cubic field driven interaction between (2)F7/2 and (2)F5/2 components [Herrmann et al., J. Appl. Phys., 1966, 37, 1312].

Concepts: Mathematics, Optics, Fundamental physics concepts, Light, Garnet

6

Isotopic discordance is a common feature in zircon that can lead to an erroneous age determination, and it is attributed to the mobilization and escape of radiogenic Pb during its post-crystallization geological evolution. The degree of isotopic discordance measured at analytical scales of ~10 μm often differs among adjacent analysis locations, indicating heterogeneous distributions of Pb at shorter length scales. We use atom probe microscopy to establish the nature of these sites and the mechanisms by which they form. We show that the nanoscale distribution of Pb in a ~2.1 billion year old discordant zircon that was metamorphosed c. 150 million years ago is defined by two distinct Pb reservoirs. Despite overall Pb loss during peak metamorphic conditions, the atom probe data indicate that a component of radiogenic Pb was trapped in 10-nm dislocation loops that formed during the annealing of radiation damage associated with the metamorphic event. A second Pb component, found outside the dislocation loops, represents homogeneous accumulation of radiogenic Pb in the zircon matrix after metamorphism. The (207)Pb/(206)Pb ratios measured from eight dislocation loops are equivalent within uncertainty and yield an age consistent with the original crystallization age of the zircon, as determined by laser ablation spot analysis. Our results provide a specific mechanism for the trapping and retention of radiogenic Pb during metamorphism and confirm that isotopic discordance in this zircon is characterized by discrete nanoscale reservoirs of Pb that record different isotopic compositions and yield age data consistent with distinct geological events. These data may provide a framework for interpreting discordance in zircon as the heterogeneous distribution of discrete radiogenic Pb populations, each yielding geologically meaningful ages.

Concepts: Atom, Sedimentary rock, Geology, Damage, Garnet, Metamorphic rock, Metamorphism, Slate

4

Transparent crystalline yttrium aluminum garnet (YAG; Y3Al5O12) is a dominant host material used in phosphors, scintillators, and solid state lasers. However, YAG single crystals and transparent ceramics face several technological limitations including complex, time-consuming, and costly synthetic approaches. Here we report facile elaboration of transparent YAG-based ceramics by pressureless nano-crystallization of Y2O3-Al2O3bulk glasses. The resulting ceramics present a nanostructuration composed of YAG nanocrystals (77 wt%) separated by small Al2O3crystalline domains (23 wt%). The hardness of these YAG-Al2O3nanoceramics is 10% higher than that of YAG single crystals. When doped by Ce3+, the YAG-Al2O3ceramics show a 87.5% quantum efficiency. The combination of these mechanical and optical properties, coupled with their simple, economical, and innovative preparation method, could drive the development of technologically relevant materials with potential applications in wide optical fields such as scintillators, lenses, gem stones, and phosphor converters in high-power white-light LED and laser diode.

Concepts: Optical fiber, Laser, Solid, Light-emitting diode, Yttrium aluminium garnet, Garnet, Yttrium, Optical materials

3

Large earthquakes occur in rocks undergoing high-pressure/low-temperature metamorphism during subduction. Rhythmic major-element zoning in garnet is a common product of such metamorphism, and one that must record a fundamental subduction process. We argue that rhythmic major-element zoning in subduction zone garnets from the Franciscan Complex, California, developed in response to growth-dissolution cycles driven by pressure pulses. Using electron probe microanalysis and novel techniques in Raman and synchrotron Fourier transform infrared microspectroscopy, we demonstrate that at least four such pressure pulses, of magnitude 100-350 MPa, occurred over less than 300,000 years. These pressure magnitude and time scale constraints are most consistent with the garnet zoning having resulted from periodic overpressure development-dissipation cycles, related to pore-fluid pressure fluctuations linked to earthquake cycles. This study demonstrates that some metamorphic reactions can track individual earthquake cycles and thereby opens new avenues to the study of seismicity.

Concepts: Earth, Geology, Earthquake, Garnet, Metamorphic rock, Seismology, Subduction, Earthquakes

1

Fractures and faults riddle the Earth’s crust on all scales, and the deformation associated with them is presumed to have had significant effects on its petrological and structural evolution. However, despite the abundance of directly observable earthquake activity, unequivocal evidence for seismic slip rates along ancient faults is rare and usually related to frictional melting and the formation of pseudotachylites. We report novel microstructures from garnet crystals in the immediate vicinity of seismic slip planes that transected lower crustal granulites during intermediate-depth earthquakes in the Bergen Arcs area, western Norway, some 420 million years ago. Seismic loading caused massive dislocation formations and fragmentation of wall rock garnets. Microfracturing and the injection of sulfide melts occurred during an early stage of loading. Subsequent dilation caused pervasive transport of fluids into the garnets along a network of microfractures, dislocations, and subgrain and grain boundaries, leading to the growth of abundant mineral inclusions inside the fragmented garnets. Recrystallization by grain boundary migration closed most of the pores and fractures generated by the seismic event. This wall rock alteration represents the initial stages of an earthquake-triggered metamorphic transformation process that ultimately led to reworking of the lower crust on a regional scale.

Concepts: Earth, Sedimentary rock, Igneous rock, Materials science, Geology, Earthquake, Garnet, Granite