Luminescence and Lasing in ZnSe Micropowders at High Optical Excitation Levels

Abstract

Photoluminescence (PL) of ZnSe wide-bandgap semiconductor micropowder was studied at a high optical excitation level by pulsed nanosecond N 2 -laser emission. A new emission band that appeared on the long-wavelength edge of the PL spectrum at 40-75 meV from the electron-hole plasma (EHP) band depending on the optical excitation level showed that plasmons could participate in recombination processes in the EHP. Random lasing at 475 nm from submicron-sized crystallites in ZnSe powder was produced by the third harmonic of a YAG:Nd 3+ laser with an exciting-radiation threshold intensity of 750 kW/cm 2 . The lasing manifested as a sharp increase of integrated emission intensity, a narrowing of the spectrum, and the appearance in it of localized and extended mode structure. Random lasing was due to feedback of amplifi ed radiation in closely packed active scattering microcrystallites. Introduction.A II B VI compounds are direct-band semiconductors and are promising for fabricating optically pumped lasers in the far-UV, visible, and mid-IR spectral regions. Quantum-sized ZnCdSe/ZnSe heterostructures are used to fabricate low-threshold green and yellow lasers with optical pumping by InGaN lasers [1]. Random lasing in the UV region at a high pulsed optical excitation level was fi rst produced and described in disordered ZnO microstructures [2,3]. Signifi cant attention is paid to random lasing in the mid-IR region in micropowders of the semiconductors ZnS, CdS, ZnSe, and CdSe activated by transition metals (Cr 2+ , Fe 3+ ) [4]. The mechanism of random lasing in nano-and microstructures (powders, thin fi lms, nanowires, etc.) of semiconductors is based on the creation of positive feedback for amplifi ed radiation with multiple scattering. As a result, closed amplifi cation loops are formed at a suffi cient level of optical excitation between the active particles of the scattering medium. Such lasers do not require mirrored cavities, which lessens signifi cantly their cost. The characteristics of random lasing are suitable for important applications of this type of lasers such as, e.g., visualization of television images, information processing and transfer, security of documents and money, labeling of materials, medical biosensors, security cameras, and illumination technologies (because microparticles of random lasers can be deposited on surfaces of any shape) [5,6]. The study of random lasing can explain processes in galactic masers, the functioning of which is based on the same feedback mechanism. Moreover, the investigation of various nano-and micropowders of media as random lasers can be used to assess preliminarily their effi ciency as active laser media.Despite numerous data on random lasing in powders of many A II B VI semiconductors, it was produced earlier only in specially undoped ZnSe micropowder [7]. The mechanisms of recombination processes in epitaxial layers and micropowders of ZnSe at high excitation levels remain obscure and determine the appearance of a new emission band on the low-energy side of the mai...

Photoluminescence and phonon spectrum studies of arsenide sulfide compound doped with rare earth elements

“…The PL lines depicted in Figure 1 are mainly related to the Fermi level and defect states located in the center of the band gap. Photoluminescence spectra in this region (at 800-950nm) were also observed in our previous work [12][13][14][15][16][17][18][19][20][21][22][23][24].…”