Revisiting the Hydrothermal growth of YAG

As new compositions and configurations of single crystals are specified for optical applications the crystal growth community must continue to optimize and explore new options for developing such materials. New crystal growth technology and a growing understanding of certain chemical and physical phenomena sometimes implore us to reconsider our perceptions even about the most studied systems. Thus, the hydrothermal growth of YAG was reexamined after nearly 40 years of inactivity and met with promising new results. While the hydrothermal growth of YAG at 500 °C was previously met with slow growth rates or poor crystal quality we have found that growth at 600–630 °C yields good quality single crystals at rates of about 0.5 mm/side/week on (100) seeds. In the current study, high quality epitaxial layers of transition metal and rare earth doped YAG have been grown from 0.1 to 2.75 mm in thickness. This has enabled several more advanced proof of concept designed growth experiments including the growth of co-doped Ca2+,Cr4+,Nd:YAG for self Q-switching, and the growth of Sm:YAG around Nd:YAG to potentially suppress amplified spontaneous emission. The interface quality of the substrate and the new growth was investigated and application of a very narrow thermal gradient at the early stages of growth has proven to greatly reduce optical scattering at the interface. The morphology of hydrothermally-grown YAG crystals is also discussed and several intermediate forms are occasionally observed.

► The hydrothermal growth of YAG is explored under new experimental conditions.
► Epitaxial layers of YAG and doped YAG 0.1–2.75 mm thick along [100] were grown.
► The growth of multifunctional and multi-zonal single crystals is demonstrated.
► Optimization of conditions is shown to reduce scattering from the growth/substrate interface.
► Several intermediate crystal forms are observed on as-grown crystals.