Studies of Process Parameters on Scale up of Nd:YAG Nanopowder Synthesis by Sol-gel Process

Scale up of process from 6 g to 200 g batch for preparation of phase pure Neodymium doped Yttrium Aluminum Garnet (Nd:YAG) nanopowder by sol-gel process using nitrate-citrate route was carried out. Optimisation of process parameters was done to resolve problems associated with large batch such as evolution of large amount of acidic fumes, increased gelation and drying time and incomplete calcination. The problem of exhaust of excess acidic fumes with size scale up was handled by passing ammonia and optimized pH of the sol. Process of drying the sol was optimised for large batch size. On scaling up from 6 g to 200 g batch incomplete crystallization was observed  on calcination under conditions optimized for 6 g batch. The causes of incomplete calcination with size scale up was identified and resolved to achieve completely crystalline particles in the range of ~25 nm to 50 nm.Defence Science Journal, 2012, 62(1), pp.199-202, DOI:http://dx.doi.org/10.14429/dsj.62.83

Nd:GGG Nanopowders by Microwave Gel Combustion Route and Sinterability Studies

Synthesis of Nd0.03Gd2.97Ga5O12 (Nd:GGG) nanopowder was carried out by microwave-assisted nitrate-citrate gel combustion technique. Various nitrate-to-citrate ratios from stoichiometric-to-fuel lean were explored. Gels were combusted by microwave heating and the combusted powders were calcined at 900 OC for 2 h. Fourier Transform Infra-red Spectroscopy (FTIR) and X-ray Diffraction (XRD) of calcined nanopowders showed phase pure Nd:GGG formation, from stoichiometric-to-fuel lean nitrate-to-citrate ratio of 1 to 0.416. Particles in the size range of 150 nm - 200 nm were obtained for stoichiometric ratio. Highly uniform, spherical morphology, with size range 90 nm - 100 nm, were obtained in fuel lean ratio of 1 to 0.416. Sintering of these nanopowders at 1550 °C for 2 h in air resulted in retention of phase purity as observed by XRD. Grain growth of less than 2 μm, for fuel lean ratio of 1 to 0.416, indicated formation of highly sinterable Nd:GGG nanopowders.Defence Science Journal, Vol. 64, No. 5, September 2014, pp.490-494, DOI:http://dx.doi.org/10.14429/dsj.64.540

Sol Freeze Dry Nd:YAG Nanopowder Synthesis and Sinterability Studies

Citrate nitrate sol freeze dry synthesis of 2 atomic % neodymium ion doped Yttrium Aluminium Oxide (Nd:YAG) nanopowders was explored for the first time. Sol was prepared by dissolving nitrates of Al3+, Y3+ and Nd3+ keeping molar ratio to be 5: 2.94: 0.06. Total metal ion to citric acid ratio was optimised at 1 is to 0.25. Sol was freeze dried at -80 °C for 48 h. Dried mass thus obtained was calcined at 1000 °C for 2 h to give phase pure Nd:YAG as characterised by FTIR and XRD. Particles were in the size range of 35 nm - 50 nm with close to spherical morphology as observed by TEM. Nanopowder was compacted and sintered at 1700 °C for 5 h under 10-6 mbar followed by hot isostatic press at 1750 °C for 4 h under 200 MPa, to give 71 per cent transmission at 1064 nm indicating synthesis of well sinterable Nd:YAG nanopowders

A novel comparative study of crystalline perfection and optical homogeneity in Nd:GGG crystals grown by the Czochralski technique with different crystal/melt interface shapes

Nd:GGG crystals (GGG is gadolinium gallium garnet) grown with different crystal/melt interface shapes (convex/flat/concave) by varying the seed rotation rate while using the Czochralski technique were studied for their optical homogeneity and crystalline perfection by optical polarization microscopy (OPM) and high-resolution X-ray diffractometry (HRXRD), respectively. It was found that there is a remarkable effect of seed rotation rate, which decides the shape of the crystal/melt interface, on the optical homogeneity and crystalline perfection. It was found experimentally that, as the rotation rate increases, the crystal/melt interface changes from convex to flat. If the rate further increases the interface becomes concave. With a steep convex interface (for low rotation rates), certain facets are concentrated in the small central portion of the crystal, and as the rate increases, these facets slowly move outward, leading to improved optical homogeneity and crystalline perfection as observed from the OPM and HRXRD results. The strain developed in the crystalline matrix as a result of segregation of oxygen in the crystals at low seed rotation rates as observed from HRXRD seems to be the reason for the observed optical inhomogeneity. The correlation between optical inhomogeneity and crystalline perfection for a variety of specimens with different shapes of the crystal/liquid interface obtained at different seed rotation rates is reported

Improved optical properties in nanocrystalline Ce:YGG garnets via normal and reverse strike co-precipitation method

There is a difference in the growth of nanoparticles based on the environment in which nucleation occurs as is observed by changing the order of reactant being added to the precipitant present in excess called the normal strike and reverse strike method. The effect of particle size on optical properties of Ce:YGG (Ce doped yttrium gallium garnet) obtained via normal and reverse strike synthesis has been investigated. The normal strike route led to smaller particle size, good chemical homogeneity as well as significant improvement in photoluminescence properties compared to the reverse strike route. A comparative study of Ce:YGG nanoparticles, synthesized via the two different methods and their optical properties are discussed. There is an enhancement in the photoluminescence efficiency in nanoparticles obtained by the normal strike method mainly due to homogeneous distribution of active ions in the host which is essential to avoid quenching