Zinc selenide

Zinc selenide
Other names Zinc selenide Stilleite
Identifiers
CAS number	1315-09-9 Y
PubChem	4298215
Properties
Molecular formula	ZnSe
Molar mass	144.35 g/mol
Appearance	light yellow solid
Density	5.27 g/cm3
Melting point	1525 °C
Solubility in water	negligible
Band gap	2.82 eV (10 ºK)
Refractive index (nD)	2.67 (550 nm) 2.40 (10.6 µm)
Structure
Crystal structure	Zincblende (cubic)
Lattice constant	a = 566.8 pm
Coordination geometry	Tetrahedral (Zn2+) Tetrahedral (Se2−)
Thermochemistry
Std enthalpy of formation ΔfHo298	−177.6 kJ/mol
Hazards
EU Index	034-002-00-8
EU classification	Toxic (T) Dangerous for the environment (N)
R-phrases	R23/25, R33, R50/53
S-phrases	(S1/2), S20/21, S28, S45, S60, S61
Related compounds
Other anions	Zinc oxide Zinc sulfide Zinc telluride
Other cations	Cadmium selenide Mercury selenide
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Zinc selenide (ZnSe), is a light yellow solid compound. It is an intrinsic semiconductor with a band gap of about 2.70 eV at 25 °C. ZnSe rarely occurs in nature. It is found in the mineral stilleite named after Hans Stille.

Properties

ZnSe can be made in both hexagonal (wurtzite) and cubic (zincblende) crystal structure.

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 doped n-type doping with, for instance, halogen elements. P-type doping is more difficult, but can be achieved by introducing nitrogen.

Applications

• ZnSe is used to form II-VI light-emitting diodes and diode lasers. It emits blue light.
• ZnSe doped with chromium (ZnSe:Cr) has been used as an infrared laser gain medium emitting at about 2.4 µm.
• It is used as an infrared optical material with a remarkably wide transmission wavelength range (0.45 µm to 21.5 µm). The refractive index is about 2.67 at 550 nm (green), and about 2.40 at 10.6 µm (LWIR). Similar to zinc sulfide, ZnSe is produced as microcrystalline sheets by synthesis from hydrogen selenide gas and zinc vapour. When especially free of absorption and inclusions it can be used particularly for CO₂ laser optics at 10.6 µm wavelength. It is thus a very important IR material. In daily life, it can be found as the entrance optic in the new range of "in-ear" clinical thermometers and can be just seen as a small yellow window. Zinc selenide can slowly react with atmospheric moisture if poorly polished, but this is not generally a serious problem. Except where optics are use in spectroscopy or at the brewster angle, antireflection or beamsplitting optical coatings are generally employed.
• 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.

Chemistry

ZnSe is insoluble in water, but reacts with acids to form toxic hydrogen selenide gas.

It can be deposited as a thin film by chemical vapour deposition techniques including MOVPE and vacuum evaporation.

External links

• II-VI - INFRARED optical data & more
• University of Reading, Infrared Multilayer Laboratory optical data