Prior to selecting a transmitting material for infrared cell use, wavelength range, solubility, and refractive index must be considered.
Thermal and mechanical properties of the material are also important. A chart describing transmission ranges, refractive index, and other useful information pertaining to crystal selection is provided in the selection guide for infrared transmitting materials. Cost is also an important factor. In the following pages, you will find economical IR transmitting crystals of the highest quality available.
| SELECTION GUIDE FOR INFRARED TRANSMITTING MATERIALS | ||||
| Materials | Transmission Range | Index of Refraction | ||
| NaCl | Rock Salt | 0.25 – 15µm | 1.52 | Generally considered the most useful cell window. NaCl is low cost and rugged. Hygroscopic. |
| KBr | Potassium Bromide | 0.25 – 25µm | 1.53 | KBr is an excellent, low cost material with an extended transmission range. It is softer than NaCl; stands thermal and mechanical shock fairly well. Hygroscopic. |
| KBr | Potassium Bromide | 0.25 – 25µm | 1.53 | KBr is an excellent, low cost material with an extended transmission range. It is softer than NaCl; stands thermal and mechanical shock fairly well. Hygroscopic. |
| AgCl | Silver Chloride | 0.4 – 23µm | 2.0 | Soft material. Darkens under UV radiation, insoluble in water. Used as inexpensive cell windows. Corrosive to metals. |
| CaF2 | Calcium Fluoride | 0.15 – 9µm | 1.40 | Low index and very low solubility. Makes durable and precise cell for the region in which it transmits. Insoluble in water; resists most acids and alkalides. Do not use with solutions of ammonium salts. |
| BaF2 | Barium Fluoride | 0.2 – 11.5µm | 1.46 | This material is extremely sensitive to thermal shock. Do not use with solutions of ammonium salts. Insoluble in water; has good resistance to fluorine and fluorides. |
| CsI | Cesium Iodide | 1.5 – 50µm | 1.74 | Generally easier to handle than cesium bromide. Hygroscopic; does not cleave; easily scratched. |
| KRS-5 | Thallium Bromide- Iodide | 0.5 – 35µm | 2.37 | Easily scratched; will cold flow; does not cleave; soluble in bases; insoluble in acids; slightly water soluble. Ideal for ATR work. Do not grind or polish. |
| ZnSe | Zinc Selenide | 1 – 18µm | 2.4 | Material equals KRS-5 in general usefulness. Insoluble in water and highly resistant to most solvents. Strong interference fringes may occur in short path cells. It is brittle and therefore must be handled with extreme care. |
| MgF2 | Magnesium Fluoride | 0.11 – 7.5µm | 1.37 – 1.38 | Slightly more soluble than CaF2. Birefringent. Transmits from vacuum ultraviolet into the infrared. Sensitive to thermal shock. |
| Ge | Germanium | 2 – 11.5µm | 4.0 | This high index material should prove highly useful for surface studies and perhaps as a process window. It is chemically inert, hard and brittle. Should be handled with extreme care, tends to fracture. |
| KCl | Potassium Chloride | 0.18 – 20µm | 1.46 | KCl is similar to NaCl, but not as popular. Our choice over NaCl for basic cell material because it is less hygroscopic, transmits further into the infrared range, and resists thermal shock. |
| ZnS | Irtran-2 Zinc Sulfide | 1 – 14µm | 2.20 | Insoluble in water. Slightly soluble in acids, HNO3, H2SO4, and KOH. |
| SiO2 | Infrasil Quartz | 0.4 – 4µm | 1.5 at 3333cm-1 | Insoluble in water. Birefringent. |