PACS 78.67.-n Photoluminescence spectra and photoluminescence excitation spectra have been measured on samples of hexagonal boron nitride microcrystalline powder, cubic boron nitride single crystal, and boron nitride nanotubes (mixture of single-walled and multi-walled with some h-BN precursor). The reason for studying these 3 samples in a comparative fashion is that nanotube BN, while based on a rolled hexagonal-BN (sp 2 -bonded) sheet, is expected to take on more sp 3 bond-character reminiscent of cubic-BN as the curvature becomes tighter. With some simplicity of statement, this study was planned to view spectroscopy of nanotube BN with respect to its two limiting cases of bond character, all measured in the same apparatus. Because of the mixed character of presently available BN nanotube samples, we consider it important to measure not just the luminescence spectra, but the tuneable-uv excitation spectra, and thereby hope to make connection with the band gaps and distinguish possible defect or impurity features.

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It is shown that the pressure treatment of boron nitride (BNsph) polycrystals a t room temperature results in the change of broad band parameters (A, B, C) and zero-phonon lines of cathodoluminescent (CL) spectra, and in the appearance of RC centers. In the pressure treated ceramic samples BNsph the PC-1 (2.84 eV), PC-2 (2.325 eV), PC-3 (1.79 eV) centers of presumably interstitial nature are found. The comparative analysis of the dependence of the broad bands parameters and zero-phonon lines of the GC centers in the CL spectra of boron nitride on pressure makes i t possible t o connect the appearance of the A and B bands in the energy range 1.85 to 3.25 eV with electronic states in the band gap due to multi vacancy complexes based on boron and nitrogen vacancies, respectively, while the appearance of the C band (1.55 t o 1.85 eV) with the plastic deformation of BN,pti.Es wird gezeigt, daB eine Druckbehandlung von Bornitrid (BNspll)-Polykristallen bei Zimmertemperatur zu einer h d e r u n g der Parameter der breiten Banden (A, B, C) und der Null-Phononenlinien der Kathodolumineszenz (CL)-Spektren und dem Auftreten von RC-Zentren fuhrt. I n den druckbehandelten keramischen BNspi,-Proben werden PC-1 (2,84 eV)-, PC-2 (2,325 eV)-und PC-3 (1,79 eV)-Zentren mit wahrscheinlich Zwischengitternatur gefunden. Die vergleichende Analyse der Druckabhangigkeit der Parameter der breiten Banden und der Null-Phononenlinien der GC-Zentren im CL-Spektrum von Bornitrid ermoglicht, das Auftreten der Aund B-Banden im Energiebereich 1,85 bis 3,25 eV mit elektronischen Zustanden in der Bandlucke infolge Mehrfach-Vakanzenkomplexe auf der Basis von Bor-bzw. Stickstoff-Leerstellen zu verkniipfen, wahrend das Auftreten der C-Bande (1,55 bis 1,85 eV) mit der plastischen Deformation von BNsph verbunden ist.

Complex and multiband photoluminescence spectra for GB and HBN centers in single crystals of cubic boron nitride (cBN) were recorded in the wavelength ranges 385-400 nm and 365-395 nm and the nature of these centers was studied. The use of models involving resonance vibrations and strongly shifted configuration diagrams for the electronic ground state and excited state made it possible to associate formation of the GB-1 center with the presence of tungsten impurity in cBN. It was established that the HBN band in the 300-350 nm range of the cathodoluminescence spectra of cBN polycrystals, single crystals, and micropowders is associated with luminescence centers present in microinclusions of graphite-like boron nitride (hBN). The nature of the hBN band is tentatively interpreted within the model of recombination of donor and acceptor defects in hBN: respectively nitrogen vacancies and carbon atoms in positions substituting for nitrogen.Key words: cubic boron nitride, photoluminescence, cathodoluminescence, nature of optically active defects, luminescence center, spectrum with complex structure, resonance vibrations, configuration diagram.Introduction. Cubic boron nitride (cBN), as a wide-gap semiconductor, is a promising material for use in electronics and optoelectronics, detectors and devices suitable for operation under high radiation and temperature conditions and also in chemically aggressive media. Since the defect and impurity structure of cBN has not been well studied, it should be quite effective to analyze it by luminescence correlated with the macroscopic characteristics of the material, taking into account the indicated practical applications.From the standpoint of basic research on cBN, of course, direct analysis of the nature of the optical transitions at the luminescence centers in cBN is of interest, including comparison with its closest Group III-Group V analogs: diamond and gallium nitride.Thus in the luminescence spectra of gallium nitride, we observe a sufficient number of features of a type associated with donor-acceptor recombination or with recombination on free or bound excitons [1]. Of course, in the indicated cases, oppositely charged impurities or defects are present simultaneously in GaN which are introduced into the material by doping or are present in the material as intrinsic defects. Effective doping of diamond is difficult, and obtaining diamond with n-type conductivity is problematic. This is explained by the lack of luminescence centers of the above-indicated type in diamond [2] and formation of many defects in diamond such that electronic transitions in them are intracenter transitions.The number of luminescence centers in cBN that have been detected so far is small compared with diamond and GaN, and only isolated centers have been thoroughly studied. Based on the hypothetical nature of the optical transitions at these centers, the overall results of luminescent studies of cBN show considerable similarity to diamond. Thus in the luminescence spectra of cBN, the predominant bands...