• A K KARNAL

      Articles written in Bulletin of Materials Science

    • Investigation on the bulk growth of $\alpha$-LiIO$_3$ single crystals and the influence of pH on its structural, morphological and optical characteristics

      A SILAMBARASAN P RAJESH P RAMASAMY A K KARNAL RAJEEV BHATT INDRANIL BHAUMIK P K GUPTA

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      $\alpha$-LiIO$_3$ is an excellent optical material exhibiting strong nonlinear optical, piezoelectric and elasto-opticproperties. However, its practical applications are limited by the insufficient reproducibility of the mentioned propertiescaused by the strong influence of the growth conditions, and, in particular, pH of the solution from which $\alpha$-LiIO$_3$3 crystal is grown. Herein, we investigate to grow bulk size good quality crystals of $\alpha$-LiIO$_3$ based on the observed problems during its crystallization process. A systematic investigation was carried out to find the effect of pH on solubility, crystal growth, structural, surface and laser damage properties of $\alpha$-LiIO$_3$ single crystals. The structure and phase of LiIO$_3$ were confirmedby powder X-ray diffractometer analysis. The functional groups of the compound were identified using Fourier transforminfrared spectroscopy. Surface defects of the grown crystals were studied by etch patterns. The crystal grown at pH 10showed 10% optical transmission enhancement in comparison to the crystals grown at pH 2. The indirect optical bandgap ofthe crystal was reinvestigated using ultraviolet–Visible–near-infrared transmittance spectrum. The laser damage thresholdstudies of the crystals grown at pH 10 reveal the higher optical radiation stability against 532 nm laser. The second-ordernonlinear optical behaviour of $\alpha$-LiIO$_3$ crystals grown at different pH conditions have been investigated by using Kurtz andPerry powder technique with Nd:YAG laser pulses at the wavelength of 1064 nm.

    • Investigations on vacuum sintered ytterbium-doped YAG ceramic: a laser–host material

      GURVINDERJIT SINGH S S RESHMA RACHNA SELVAMANI V S TIWARI A K KARNAL

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      Laser–host ceramics are a new class of materials and have proved to be a good alternative to the single-crystals. They can be produced in large size with higher concentration of activator ions having more homogeneity which is difficultto achieve with the conventional single-crystal growth technology. Ytterbium (Yb)-doped yttrium aluminium garnet (YAG) is a very attractive laser–host material because of its broad emission band, low quantum defect, no excited state absorption or up-conversion loss and wide range of tunability. In the present work, 10 atm% Yb-doped YAG transparent ceramic was fabricated using nano-powder technology and vacuum sintering. Single-phase nano-powders of Yb:YAG were synthesized by a co-precipitation method and thereafter sintered under vacuum at 1750$^{\circ}$C for 5 h. The as-sintered ceramic samples are ofdark greenish colour which is attributed to the reduction of Yb$^{3+}$ to Yb$^{2+}$ during vacuum sintering. However, after annealing in air at 1350$^{\circ}$C for 8 h they retain their natural colour attributed to the transformations from Yb$^{2+}$ to Yb$^{3+}$. The transmission spectra of the as-sintered polished ceramics show the presence of broad absorption bands near 250, 380, 480 and 630 nm due to the electronic transitions in the Yb$^{2+}$ ion. These bands disappear after annealing in air. The well-established bandsdue to transitions in Yb3+ were observed between 900 and 1000 nm.

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