Kinetic features of optically stimulated luminescence in aluminum nitride powder

Abstract

In addition to traditional applications in optoelec tronics, aluminum nitride (AlN) single crystals and related ceramic materials are also considered promis ing media for highly sensitive detectors of β and UV radiation [1][2][3]. Results of investigations of the thermo (TL) and photoluminescence (PL) of AlN showed evidence of a complex character of relaxation processes upon the excitation and revealed limitations for the practical use of this material in personal dosim etry (pronounced feeding, nonlinear dose depen dence, etc.) [2][3][4]. As is known, the spectrum of useful dosimetric response of AlN falls in the UV and visible wavelength range and is typically related to recombi nation processes involving vacancies and impurity defects (V Al , O N , and related complex defects) [2, 4⎯6].The TL and PL properties of AlN have been exten sively studied in various structural states, including ceramics, films, single crystals, powders, and nano rods [2][3][4]. However, the kinetics of relaxation pro cesses-in particular, those accompanying optical excitation-has not been profoundly analyzed in the framework of quantitative models until now. This analysis can provide additional information about the mechanisms of relaxation in AlN upon photoexcita tion, mechanisms of dosimetric signal accumulation and storage, and mechanisms of accumulated energy transfer between metastable centers of trapping and recombination of charge carriers.In this context, the present investigation was aimed at the analysis and quantitative estimation of laser induced luminescence in UV irradiated AlN powders.The experiments were performed on AlN powder with grain sizes within 0.2-0.8 μm, which was obtained by the subfluoride method [7]. The powder was synthesized from chemically pure aluminum fluo ride (State Standard TU 6 09 11 22 84, Ural Galo gen Co.) and granulated aluminum (A98 grade, Ural Chemical Reagent Plant). The synthesized powder contained no intentionally introduced impurities. According to the results of chemical analysis, the main impurities in the as synthesized material were carbon (0.39 wt %) and oxygen (0.1 wt %). The powder was pressed into 2 mm deep copper cups with an internal diameter of 10 mm and a wall thickness of 2 mm. Prior to experiments, the samples were annealed at 773 K.The samples were irradiated by UV light of a high pressure mercury vapor lamp (DRT 230) via an opti cal glass filter (EFS 1), which ensured a transmission band within 5.16-2.95 eV. The UV radiation dose was varied by controlling the sample exposure time t uv . The afterglow, optically stimulated luminescence (OSL), and TL measurements were performed on an original spectrometric setup. The spectral range of interest was separated using a set of optical glass filters (UFS 1, SZS 22), which provided a maximum transmission of 38.5% at a photon energy of 3.25 eV and a full width at half maximum (FWHM) of 0.27 eV. The emission was detected by an FEU 39A photomultiplier operating in the photon count mode. The OSL was induced by a red laser operating at...

Continuous wave OSL in bulk AlN single crystals

“…3). Note, that AG is typical for different structures of the irradiated AlN and is present already before switching on the laser [11,17]. After initiation of stimulation ("laser on") the emission intensity increases dramatically and cumulative "OSL + AG" signal is registered (Fig.…”

“…It is known that intrinsic and impurity defects of the anion sublattice (V N -and O N -centers) determine emission activity of AlN in the UV/Vis spectral range and help to detect and store dosimetric information [12][13][14][15]. Recently within the framework of formal kinetics analysis of the TL processes involving the above mentioned centers the values of the activation energy and effective frequency factor have been obtained [10,13]; and dose dependences of the TL and OSL response have been analyzed [16,17]. However, the basic parameters responsible for mechanisms of optically stimulated emission of oxygen-related complexes in bulk aluminum nitride have not been studied enough.…”

“…AG affects essentially the CW-OSL dose dependences of the AlN powder and ceramics under UV-irradiation and the nonlinear dose dependence is assigned to the fading during irradiation [16,17]. Note that the observed afterglow is one of the channels for fading of dosimetric infor- , responsible for С1 and С2 components, respectively, in the OSL signal, was evaluated.…”