Investigation of the Y centers in cubic plastically deformed type Ib diamonds (Yakutia placers)

Abstract

For a series of cubic type Ib diamond crystals from Yakutia placers, the interaction of Y centers with radiation defects has been studied and the effect of annealing at high-pressure high-temperature (HPHT) conditions on the infrared (IR) spectra of Y centers has been investigated. It is shown that as a result of electron irradiation and heat treatment at 1000 °C, the intensity of the IR band in the region of 1140–1150 cm⁻¹ (Y center) decreases and the H3 photoluminescence (PL) system (defect representing two nitrogen atoms around vacancy) arises, while the intensity of the IR band at 1282 cm⁻¹ (A center) remains almost unchanged. It is proposed that the H3 defect can be produced by the interaction of vacancy with the Y center. The suitable model for the Y center is a neutral N1 defect (nitrogen pair separated by one carbon atom), which is the limiting stage in the aggregation sequence of impurity nitrogen into the A form. For a neutral N1 structure, a higher energy barrier has to be overcome due to the Coulomb repulsion compared to the diffusion of nitrogen in the bulk crystal volume. The low content of A centers and the presence of nitrogen in the form of neutral N1 defects provide evidence of a sufficiently low growth temperature of the studied diamonds. The crystals have been annealed at HPHT conditions, and prior to the C centers, the Y centers transform into A defects. These results support the proposed model of the Y center as having two nitrogen atoms in proximity to each other (NCN). The IR band at 1332 cm⁻¹ (N⁺ defect) does not anneal out even at a temperature of 2000 °C which indicates the presence of electron acceptors that remain stable at these treatment temperatures. The corresponding acceptor centers can be carbon broken bonds in the dislocation cores. The unusual properties of the N⁺ states and the birefringence patterns in the studied diamonds evidence the plastic deformation of the crystals under study.