The results of a systematic study of photoluminescence (PL) properties of un‐doped sapphire crystals grown using different starting materials on various crystal growth methods (CZ, EFG, HDSM, Kyropoulus, HEM) are presented. Narrow line of emission has been attributed to radiation transition in Cr3+ ions (R‐line), while the nature of red wide band (RWB) of emission (600‐850 nm) is still under question. Integral intensities of R‐line and RWB were analyzed and their dependences on type of starting raw materials and of the method of crystal growth were shown. The crystals grown using Vernuil starting material exhibited significant PL in all utilized methods. On the contrary, sapphire samples grown by the same technologies wherein EMT HPDAR (High Purity Densified Alumina) was the starting material revealed much lower PL. HPDAR is produced by EMT, Inc. with proprietary and patented technology. The concentrations of various metal impurities such as Ca, Mg, Zn, Cu, Cr, Fe, Ni, H were measured. Effect of these impurities on luminescence intensity and especially the role of hydrogen incorporated into sapphire lattice are discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

No abstract

Sapphire is a widely used material for optical, electronic and semiconductor applications due to its excellent optical properties and very high durability. Optical and mechanical properties of sapphire depend on many factors such as the starting materials that are used to grow crystals, methods to grow sapphire crystals, etc. Demand for highest purity and quality of sapphire crystals increased ten fold for the last several years due to new applications for this material. In this work we studied the effect of starting materials and crystal growth methods on the optical and mechanical properties of sapphire, especially concentrating on the effect of hydrogen on the properties of sapphire. It was found that the infrared (IR) absorption which is traditionally used to measure the hydrogen content in sapphire crystals cannot be reliably used and the data obtained by this method provides a much lower hydrogen concentration than actual. We have shown for the first time that Nuclear Magnetic Resonance techniques can be successfully used to determine hydrogen concentration in sapphire crystals. We have shown that hydrogen concentration in sapphire can reach thousands of ppm if these crystals are grown from Verneuil starting material or aluminum oxide powder. Alternatively, the hydrogen concentration is very low if sapphire crystals are grown from High Purity Densified Alumina (HPDA ®) as a starting material. HPDA ® is produced by EMT, Inc through their proprietary patented technology. It was found that optical and mechanical properties of sapphire crystals grown using EMT HPDA ® starting material are much better than those sapphire crystals grown using a starting material of Verneuil crystals or aluminum oxide powder.

No abstract