Crystal Growth and Photoluminescence Properties of Reactive CVD-Derived Monoclinic Hafnium Dioxide

Abstract

Here we report the first synthesis of large-size (up to 2 cm), transparent, high-purity monoclinic HfO2 single crystals by reactive chemical vapor deposition (RCVD) using CF4 as a transport agent at 1000 °C. The single crystals were comprehensively characterized in terms of their phase and elemental composition, as well as morphology by the modern analytical techniques. Thermodynamic modeling of the Hf–C–Si–O–F heterogeneous system was undertaken to understand in detail the chemical equilibria that occur in this transport system. Based on modeling results, it was shown that HfO2 formation occurs through HfOF2 decomposition. Morphological peculiarities of RCVD-derived HfO2 single crystals were studied by optical and scanning electron microscopy. Vicinal hills and numerous growth steps were observed on the crystal surfaces. The HfO2 single crystals exhibit strong and broad emission under UV excitation. The fit of the broad optical emission into spectral components allowed us to identify the nature of emission and assign it to the intrinsic defects of crystals. The successful synthesis of plate-like high-purity monoclinic HfO2 single crystals may provide some insight into the design of optical or other devices.

New Ablation-Resistant Material Candidate for Hypersonic Applications: Synthesis, Composition, and Oxidation Resistance of HfIr3-Based Solid Solution

“…First, these are monolithic ceramics based on hafnium-containing compounds such as HfC, HfN, and HfB 2 . The product of the oxidation of these compounds is hafnium dioxide, which is among the most refractory oxides and has the lowest vapor pressure at T = 2400 K ( P = 1.5 × 10 –7 atm , ). − Much attention was also paid to the research and development of the materials based on HfB 2 or ZrB 2 in conjunction with SiC. They were identified as the most appropriate oxidation-resistant refractory materials at temperatures above 1800 °C. , …”

Thermal quenching of self-trapped exciton luminescence in nanostructured hafnia

“…According to calculations [37,38], oxygen vacancies in positions of O 3f and O 4f in different charge states create additional energy levels in the forbidden gap, and corresponding optical transitions involve in forming spectral features of the OA spectrum. At hν > 5.5 eV, a sharp increase in absorption corresponds to the region of the intrinsic absorption edge, which is typical for the monoclinic hafnium dioxide [5,9,13,17,20,23,28,29,39] and quite coincides with the excitation energy of STE (see Figures 3 and 4).…”

“…Thus, it can be inferred that the intrinsic absorption edge in nominally pure hafnium dioxide is formed by direct and indirect allowed band-to-band transitions alike. The possibility of simultaneous realization of two types of optical transitions has been previously revealed in thin films [9,20] and m-HfO 2 single crystals [13]. According to [41,42] an indirect allowed transition occurs between the points Γ → Β of the Brillouin zone, and the direct one corresponds to the process Γ → Γ.…”

“…Thus, the monoclinic-phase structures as the most stable and the most common ones under atmospheric conditions are of greatest interest for research. From the point of view of the experimental study of perfect simulation objects, only one work is today known for the authors to judge synthesized and investigated optical properties of monoclinic single crystal hafnium dioxide [13]. Meanwhile, commercial high-purity-degree powders (99.9%) are often used for analyzing physical and chemical properties [14][15][16].…”

Latent Fingerprint Imaging Using Dy and Sm Codoped HfO2 Nanophosphors: Structure and Luminescence Properties

“…The emission peaks located at 568 and 577 nm lying in yellow or green region arise when excited electrons relax directly from 4 G 5/2 to 6 H 5/2 , ground state, whereas peaks in the wavelength range of 597–617 nm in near red region appear due to electronic transition, 4 G 5/2 → 6 H 5/2 . Additionally, one can notice a sharp peak at 557 nm predominantly associated to transitions occurring from different defect levels within the host, HfO 2 …”