Photoluminescence and surface photovoltage spectroscopy studies of hydroxyapatite nano-bio-ceramics

Photolummescence (PL) and surface photovoltage spectroscopy applied to nanostructural bioceramics hydroxyapatite (HAp) allowed to study electron (hole) energy states spectra of HAP and distinguish bulk and surface localized levels. Studied PL excitation spectra allowed obtaining an exact value of the energy band gap in HAP: E-g = 3.95 eV,This result is consistent with E-g value determined by the contact potential difference (ACPD) curves treatment method as E-g = 3.94 eV. Comparison between ACPD and PL spectra indicates that the energy spectra of electron - hole levels studied by two different experimental spectroscopy techniques are very similar. This comparison enables to conclude that all HAp samples have identical electron - hole states structures consisting of five bulk states and one surface state. It is assumed that the deep electron (hole) charged states may be responsible for high bioactivity of the HAp nanoceramics. (c) 2006 Elsevier B.V. All rights reserved.