T. Yanagitani

Bio: T. Yanagitani is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 59 citations.

The optical properties and laser characteristics of Cr3+ and Nd3+ co-doped Y3Al5O12 ceramics

Abstract: We have fabricated Cr 3+ and Nd 3+ co-doped YAG (Cr;Nd:YAG) ceramics, and investigated their optical properties and laser characteristics. The Cr;Nd:YAG has two broad absorption bands at around 440 nm ( 4 A 2 → 4 T 1 ) and 600 nm ( 4 A 2 → 4 T 2 ) respectively, caused by Cr 3+ ions. In the case of pumping at 440 nm, the maximum effective lifetime of the Cr;Nd:YAG was 737 μs with a 0.1 at% Cr 3+ and 1.0 at% Nd 3+ co-doped YAG sample. Cr 3+ ions take a role of an effective sensitizer to convert the UV light of flashlamp. For single-shot laser operation, a 10.4 J output energy at 1064 nm was obtained with 0.1 at% Cr 3+ and 1.0 at% Nd 3+ co-doped YAG ceramic rod with a laser efficiency of 4.9%. The laser efficiency was found to be more than twice that of a 1.0 at % Nd 3+ :YAG ceramic rod.

Materials development and potential applications of transparent ceramics: A review

Abstract: Transparent ceramics have various potential applications such as infrared (IR) windows/domes, lamp envelopes, opto-electric components/devices, composite armors, and screens for smartphones and they can be used as host materials for solid-state lasers. Transparent ceramics were initially developed to replace single crystals because of their simple processing route, variability in composition, high yield productivity, and shape control, among other factors. Optical transparency is one of the most important properties of transparent ceramics. In order to achieve transparency, ceramics must have highly symmetric crystal structures; therefore, the majority of the transparent ceramics have cubic structures, while tetragonal and hexagonal structures have also been reported in the open literature. Moreover, the optical transparency of ceramics is determined by their purity and density; the production of high-purity ceramics requires high-purity starting materials, and the production of high-density ceramics requires sophisticated sintering techniques and optimized sintering aids. Furthermore, specific mechanical properties are required for some applications, such as window materials and composite armor. This review aims to summarize recent progress in the fabrication and application of various transparent ceramics.

Highly efficient solar-pumped Nd:YAG laser.

Abstract: The recent progress in solar-pumped laser with Fresnel lens and Cr:Nd:YAG ceramic medium has revitalized solar laser researches, revealing a promising future for renewable reduction of magnesium from magnesium oxide. Here we show a big advance in solar laser collection efficiency by utilizing an economical Fresnel lens and a most widely used Nd:YAG single-crystal rod. The incoming solar radiation from the sun is focused by a 0.9 m diameter Fresnel lens. A dielectric totally internally reflecting secondary concentrator is employed to couple the concentrated solar radiation from the focal zone to a 4 mm diameter Nd:YAG rod within a conical pumping cavity. 12.3 W cw laser power is produced, corresponding to 19.3 W/m2 collection efficiency, which is 2.9 times larger than the previous results with Nd:YAG single-crystal medium. Record-high slope efficiency of 3.9% is also registered. Laser beam quality is considerably improved by pumping a 3 mm diameter Nd:YAG rod.

Greatly enhanced Dy3+ emission via efficient energy transfer in gadolinium aluminate garnet (Gd3Al5O12) stabilized with Lu3+

Abstract: Dy3+-doped and Lu3+-stabilized gadolinium aluminate garnet solid solutions of [(Gd1−xLux)1−yDyy]3Al5O12 (x = 0.1–1.0, y = 0–0.10) have been developed as efficient phosphors for simultaneously strong blue (∼483 nm, the 4F9/2 → 6H15/2 transition of Dy3+) and yellow (∼584 nm, the 4F9/2 → 6H13/2 transition of Dy3+) emissions. The efficient energy transfer from Gd3+ to Dy3+ produces an additional excitation band, being the strongest, at ∼275 nm that corresponds to the 8S7/2 → 6IJ intra-f–f transition of Gd3+. With the energy transfer, significantly stronger Dy3+ emission (roughly two-fold) was obtained through excitation of Gd3+ at 275 nm rather than direct excitation of Dy3+ at 352 nm (6H15/2 → 4I11/2 + 4M15/2 + 6P7/2 transition, the strongest intra-f–f transition of Dy3+). The quenching concentration of Dy3+ was determined to be ∼2.5 at%, and the quenching mechanism was suggested to be dipole–dipole interactions. At the optimal Dy3+ content of 2.5 at%, increasing Lu3+ substitution tends to weaken both the excitation and emission bands owing to the higher electronegativity of Lu3+. Comparative studies showed that the best luminescent [(Gd0.8Lu0.2)0.975Dy0.025]AG phosphor has an integrated emission intensity roughly 2.5 and 4 times those of its (Y0.975Dy0.025)AG and (Lu0.975Dy0.025)AG counterparts, respectively. The effects of processing temperature and Lu3+/Dy3+ contents on phase evolution, crystal structure, particle morphology, PLE/PL properties, and fluorescence lifetime of the phosphor are thoroughly investigated. Owing to its enhanced emission and high theoretical density, the (Gd,Lu)AG:Dy3+ phosphor developed in this work may potentially be used as a new type of photoluminescent and scintillation material.