LUMINESCENCE OF THULIUM-ACTIVATED CUBIC BORON NITRIDE E. M. Shishonok, a* L. Trinkler, b S. V. Leonchik, a and B. Berzinya b UDC (535.37+543.42):548 Under high pressure and temperature conditions, we have obtained samples of thulium-activated cubic boron nitride in the form of micropowders, ceramics, and polycrystals activated by thulium in the presence of alu- minum. We studied the cathodoluminescence (CL), photoluminescence (PL), and photoluminescence excitation spectra of the samples. In the luminescence spectra we observe structured bands with maxima at ~370, ~475, ~660, and ~800 nm, assigned to electronic transitions in the triply charged thulium ions. We have established that the most efficient method for excitation of "blue" luminescence at ~475 nm for thulium ions in cBN is excitation by an electron beam. The cBN samples synthesized in the presence of Al have photoluminescence spectra with a more complex structure compared with samples not containing Al, with the band of dominant intensity at about 660 nm. Hypothetically, this is a consequence of incorporation of thulium ions into the crystalline phases cBN and AlN, which are equally likely to be formed during synthesis. The observed pho- toluminescence spectrum of the indicated samples is the superposition of the photoluminescence spectra of the Tm 3+ ions located in the crystal fields of cBN and AlN of different symmetries. The presence in the photolu- minescence excitation spectra (at 450, 490, and 660 nm) of structure, with features at wavelengths shorter than the excited photoluminescence, suggests a nonresonant mechanism for its excitation. We have established that luminescence of Tm 3+ ions is less intense than for other rare earth elements incorporated into cubic boron nitride. Key words: cubic boron nitride, photoluminescence, photoluminescence excitation spectrum, thulium, electronic transitions. Introduction. Cubic boron nitride (cBN) is a semiconductor with the widest bandgap (∆ = 6.4 eV) in the A III B V group of compounds and is the closest analog to diamond. It surpasses diamond in bandgap width, thermal sta- bility, radiation resistance, and chemical stability, the potential for forming n-type and p-type conductivities, and the ability to emit secondary electrons. Today materials are being actively studied and used that are activated by rare earth elements, in particular by thulium (Tm). Among these materials, an important position is occupied by nitrides (gallium nitride, aluminum nitride) activated by thulium, having intense emission in the blue range of the spectrum. This is why GaN and AlGaN are used in electroluminescent optical devices (blue light-emitting diodes, white light emitters, full-color displays). Tm-ac- tivated materials are used for conversion of IR emission to blue emission [1–6] and in solid-state lasers [7]. Analysis of known data showed that the main peaks in the electroluminescence (EL) spectra of GaN thin films are detected at ~475 and ~800 nm, and correspond to electronic transitions from the excited states 1 G 4 and 3 F 4 to the ground state 3 H 6 . The intensity of electroluminescence increases as the applied voltage increases, while the ratio of the intensities of the bands changes in favor of the band at ~475 nm [8–10]. Simultaneous optical (UV) pumping and application of an electric voltage makes it possible to increase the electroluminescence intensity. Cathodolumines- cence of GaN Tm films grown by the MOCVD method [11] identified two bands in the spectra: a low-intensity band at ~475 nm and an intense band at ~800 nm. a Scientific Production Association/Belarus Scientific and Applied Materials Research Center, 19 ul. P. Brovki, Minsk, 220072, Belarus; e-mail: shishonok@ifttp.bas-net.by; b Institute of Solid State Physics, Latvian University, Riga. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 547–555, July–August, 2008. Original article submitted February 11, 2008. Journal of Applied Spectroscopy, Vol. 75, No. 4, 2008 0021-9037/08/7504-0374 ©2008 Springer Science+Business Media, Inc. 567 ∗ To whom correspondence should be addressed.