Electrostatic, Luminescent, and Paramagnetic Responses of Fresh BN Nanopowders Synthesized under Concentrated Light

TL;DR

This paper investigates the unique electrostatic, luminescent, and paramagnetic properties of BN nanopowders synthesized under high-temperature optical furnace conditions, and how these properties diminish over time due to surface oxidation and environmental exposure.

Contribution

It provides new insights into the surface chemistry and stability of BN nanopowders synthesized under non-equilibrium conditions, emphasizing the role of surface defects in functional properties.

Findings

Initial nanopowders exhibit strong electrostatic, luminescent, and paramagnetic responses.

These properties diminish significantly after two years of air exposure due to surface oxidation.

Commercial BN powders show similar loss of magnetic resonance features over time.

Abstract

This study explores the properties of nanopowders synthesized under high-temperature, non-equilibrium conditions in a high-flux optical furnace in a nitrogen flow. Boron powders served as the starting material, and the intense thermal gradients during synthesis led to incomplete chemical reactions. As a result, the surface of the resulting nanoparticles is covered with a thin layer of sassolite, followed by boron oxides, beneath which lies a boron nitride shell. The subsurface contains boron-rich nitride phases, while the core consists of elemental boron. For reference, commercial platelet-like h-BN powders from the "Chempur" company were also analyzed. Initially, all synthesized nanopowders displayed pronounced electrostatic charging, photoluminescence (PL), and paramagnetic activity, attributable to high surface defect densities and unsaturated chemical bonds. However, after two years of exposure to ambient air, these nanopowders exhibited complete loss of electrostatic charging, absence of photoluminescence (PL), and disappearance of the characteristic single EPR resonance line. Similarly, commercial h-BN nanopowder from the "Chempur" company does not exhibit a single EPR resonance line too. FTIR analysis revealed progressive surface oxidation and hydroxylation of this powder, suggesting that atmospheric moisture and oxygen effectively passivated defect states. These findings underscore the critical role of surface chemistry in governing the electrostatic, optical, and magnetic behavior of BN-based nanomaterials and highlight the importance of defect stabilization for preserving functional properties over time.