Photoluminescence, surface photovoltage spectroscopy and high-resolution characterization methods (Atomic Force Microscopy, Scanning Electron Microscopy, X-ray spectroscopy and DC conductivity) are applied to nanostructured Hydroxyapatite (HAp) bioceramics and allowed to study electron (hole) energy states spectra of the HAp and distinguish bulk and surface localized levels. The measured trap spectra show strong sensitivity to preliminary heat treatment of the ceramics. It is assumed that found deep electron (hole) charged states are responsible for high bioactivity of the HAp nanoceramics.

We describe the effect of nanoscale spatially coupled trapping centre (TC)-luminescent centre (LC) pairs on the thermoluminescence (TL) properties of LiF : Mg,Ti. It is shown that glow peak 5a (a low-temperature satellite of the major glow peak 5) arises from localized electron-hole (e-h) recombination in a TC-LC pair believed to be based on Mg 2+-Li vac trimers (the TCs) coupled to Ti(OH) n molecules (the LCs). Due to the localized nature of the e-h pair, two important properties are affected: (i) heavy charged particle (HCP) TL efficiency: the intensity of peak 5a relative to peak 5 following HCP high-ionization density irradiation is greater than that following low ionization density irradiation in a manner somewhat similar to the ionization density dependence of the yield of double-strand breaks (DSBs) induced in DNA. Our experimental measurements in a variety of HCP and fast neutron radiation fields have demonstrated that the ratio of glow peaks 5a/5 is nearly independent of particle species for the protons, deuterons and He ions investigated, is somewhat dependent on HCP energy, and is roughly 2-3 times greater than the peak 5a/5 ratio in low ionization density electron and photon fields. The intensity ratio of peak 5a/5 thus has the potential of estimating the ratio of dose deposited via high ionization density interactions compared to low ionization density interactions in a nanoscale volume without any prior knowledge of the characteristics of the radiation field, (ii) non-linear TL dose response: the relative lack of competitive processes in the localized recombination transitions leading to the TL of composite peak 5 versus the dose-dependent competitive processes in conduction band-mediated delocalized luminescence recombination leads to non-linear dose response (supralinearity) for composite peak 5 and a dependence of the supralinearity on ionization density. This behaviour is modelled in the framework of the unified interaction model (UNIM).

This paper presents a classification of the processes of slow electron emission in solids when excited and stimulated in different ways. All these processes belong to the so‐called exoelectron emission (EEE). We examine phenomenological theories which explain the basic experimental evidence of the non‐stationary thermoemission (TEE). The EEE is described in terms of a kinetic theory close to luminescence theory. The experimental criteria suggested for distinguishing different types of exoelectron emission mechanisms can be used for any broad‐band emitters.

No abstract

The composite structure of glow peak 5 in LiF:Mg,Ti (TLD-100), has been investigated using optical bleaching by 310 nm (4 eV) light. The decay of composite peak 5 and the growth of peak 4 are described by two exponential components of the same mean lives for both peaks. Using computerized glow curve deconvolution and contrary to previous investigations, it is determined that peak 4 does not decrease in intensity at long bleaching times and is therefore not associated with the 4 eV absorption band. The fast and slow components of the exponential decay are associated with the bleaching of peaks 5a and 5, respectively. Optical bleaching as a function of the temperature of post-irradiation annealing reveals that the conversion efficiency of peak 5a to peak 4 is very high, at a constant value of approximately 30%, whereas the conversion efficiency of peak 5 is no greater than a few per cent. The behaviour of the conversion efficiency as a function of the temperature of the post-irradiation anneal is explained in the framework of the spatially correlated trapping centre/luminescent (TC/LC) centre model. In this model, the TL of peak 5a results from the geminate recombination of a locally trapped electron-hole pair: peak 5 results from recombination via electron diffusion in the conduction band following thermal release of a singly-trapped electron in the TC/LC structure. Peak 4 arises from a singly-trapped hole in the TC/LC structure. The high conversion efficiency of peak 5a to peak 4 arises from direct optical ionization of the electron in the electron-hole pair, leaving behind a singly-trapped hole (glow peak 4), a direct mechanism not subject to competitive processes. Optical ionization of the `singly-trapped' electron (peak 5), however, can lead to peak 4 only via a multi-stage mechanism involving charge carrier transport in the conduction band, a mechanism subject to competitive processes, which leads to an order-of-magnitude decrease in the observed efficiency