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Cadmium selenide is a hexagonal crystal with wurtzite structure. Synthetic crystals of such kind are grown from vapor-phase phase and are black in color.
Cadmium selenide is transparent in the range between 0.75 μm and 24.5 – 25.5 μm. Due to that, parts made of cadmium selenide can be used in near and mid-IR. Upper limit of the transparency range is determined by the lattice absorption of the material.
Figure 1. Transmission spectrum of monocrystalline cadmium selenide
For some crystallographic orientations, the hexagonal structure of the crystal exhibits natural birefringence. Therefore, these crystals can be used to produce waveplates of various orders.
Moreover, cadmium selenide is virtually the only material that is birefringent in the range between 16-24 μm.
Cadmium selenide has low absorption coefficient. Therefore, its crystals can be used in non-linear optical transformers and parametric oscillators where the radiation load is high.
Table 1. Key physical properties of optical-grade monocrystaline cadmium selenide
|Crystal structure||Hexagonal, space group P63mc, point group 6mm|
|Primitive cell dimensions, Å||a=4.298, b=7.013|
|Refractive indices||no=2.339, ne=2.351 @22 μm
no=2.399, ne=2.419 @16 μm
no=2.431, ne=2.452 @10 μm
no=2.446, ne=2.466 @5 μm
no=2.461, ne=2.479 @2.4 μm
no=2.482, ne=2.501 @1.6 μm
no=2.645, ne=2.661 @0.8 μm
|Optical absorption, cm-1 (@ 10.6 μm)||<1×10-2|
|Dislocation density, cm-2||<5×104|
|Curie temperature, °C||503|
|Melting point, °C||1537|
|Thermal expansion coefficients (@25°С), K-1||||c=2.45х10-6, ⊥ c=4.4х10-6|
|Thermal conductivity, W/(m × K)||||c=6.9, ⊥ c=6.2|
|Specific heat capacity, J/(kg × K)||258|
|Elastic constants, GPa (@298 K)||СE11=74.1, CE33=83.6, CE44=13.17, CE12=45.2, CE13=39.3|
|Piezoelectric constants, C/N||D33=7.81×10-12, D15=-10.1×10-12, D31=3.8×10-12|
|Dielectric constants (@300 K)||εT11/ε0=9.7, εT33/ε0=10.65,
|Linear electrooptic coefficients, m/V||rS13=1.8×10-12, rS33 =4.8×10-12|
|Nonlinear optic coefficients, m/V (@ 10.6 μm)||d33=55х10-12, d31=-28 х10-12, d15=31 х10-12|
|Sellmeier equation coefficients (λ in μm)||no2=4.1321+1.8587λ2/(λ2-0.2187)+ 3.0461λ2/(λ2-3380)
|Solubility||Soluble in hot nitric and phosphoric acid. Insoluble in water|
The properties of CdSe optical parts produced by our company are listed below:
Please pay attention that this article is only for your information. We do not supply raw cadmium selenide as well as semi-finished products. Our standard products are finished (polished, coated) parts.
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