Zinc selenide is the inorganic compound with the formula ZnSe. It is a lemon-yellow solid although most samples have a duller color due to the effects of oxidation. It is an intrinsic semiconductor with a band gap of about 2.70 eV at , equivalent to a wavelength of 459 nm. ZnSe occurs as the rare mineral stilleite, named after Hans Stille.
Synthesis and properties ZnSe is available in both hexagonal (wurtzite) and cubic (zincblende) polymorphs. In both cases, the Zn2+ and Se2− sites are tetrahedral. The difference in the structures related to close packing motifs, hexagonal vs cubic.
Cubic ZnSe is produced by treatment of an aqueous solution of zinc sulfate with hydrogen selenide:
Heating the cubic form gives hexagonal ZnSe.
An alternative synthesis involves heating a mixture of zinc oxide, zinc sulfide, and selenium:
It is a wide-bandgap semiconductor of the II-VI semiconductor group (since zinc and selenium belong to the 12th and 16th groups of the periodic table, respectively). The material can be n-type doped with, for instance, halogen elements. P-type doping is more difficult, but can be achieved by introducing gallium.
Similar to zinc sulfide, ZnSe is produced as microcrystalline sheets by synthesis from hydrogen selenide gas and zinc vapour. Another method of producing is a growth from melt under excessive pressure of inert gas (Ar usually).
It can be deposited as a thin film by chemical vapour deposition techniques including MOVPE and vacuum evaporation.
Reactions ZnSe is insoluble in water, but dissolves in concentrated hydrochloric acid giving hydrogen selenide gas.
Zinc selenide can slowly react with atmospheric moisture if poorly polished - as it is gradually hydrolyzed by moisture giving the faint rotten garlicky odor of hydrogen selenide at trace amounts. This is not generally a serious problem. Except where optics are used in spectroscopy or at the Brewster angle, antireflection or beamsplitting optical coatings are generally employed.
Applications Zinc selenide has a few commercial applications for its optical properties. Its wide transmission wavelength range (0.45 μm to 21.5 μm recommends it as an IR material (windows).https://web.archive.org/web/20190422005411/http://www.kayelaby.npl.co.uk/general_physics/2_5/2_5_8.html Kaye and Laby online at NPL via archive.org). The refractive index is about 2.67 at 550 nm (green), and about 2.40 at 10.6 μm (LWIR).
Its luminescence properties have been well investigated.
ZnSe doped with chromium (ZnSe:Cr) is an infrared laser gain medium, emitting at about 2.4 μm.Cr2+ excitation levels in ZnSe and ZnS, G. Grebe, G. Roussos and H.-J. Schulz, J. Phys. C: Solid State Phys. vol. 9 pp. 4511-4516 (1976)
ZnSe activated with tellurium (ZnSe(Te)) is a scintillator with emission peak at 640 nm, suitable for matching with photodiodes. It is used in x-ray and gamma ray detectors. ZnSe scintillators are significantly different from the ZnS ones.
References
External links Coherent Optical Data optical data & more