Contents:
Possible Alternative Materials to ThF4
Safety and Handling
Comparative Comments
Forms and Sizes Available
Other Coating Materials
Comparisons Between Thorium Fluoride and Replacement Materials

FLUORINE COMPOUNDS FOR 10µm APPLICATIONS

Introduction
Thorium fluoride provides the lowest absorption at 10.6µm wavelength and has been the mainstay for high energy applications where high damage thresholds are required. Because thorium fluoride is a naturally radioactive material and special handling and disposal procedures must be followed, continuing searches are underway for alternate, non-radioactive substitutes.

Possible Alternative Materials to ThF₄
Many applications do not require the lowest possible absorption. Consequently, other fluorine compounds may be useful in certain areas. The accompanying table lists three alternate choices: yttrium fluoride, CERAC IRB^TM and CERAC IRX^TM. Aside from low absorption, these fluorides have sufficiently low refractive indices to satisfy that requirement in high efficiency anti-reflection coatings.

All of the suggested fluoride compounds can be evaporated by resistance-heating or e-beam techniques. Each of these materials should be preconditioned for several minutes at low power until pressure changes and spitting subsides. Of the three compounds listed, only thorium fluoride sublimes. The others melt.

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Safety and Handling
ThF₄ is naturally radioactive and must be handled in accordance with established regulations.

YF₃, IRB^TM and IRX^TM can all be handled with no special precautions, except the usual concern for dust inhalation.

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Comparative Comments

YF3	IRBTM	IRXTM
Serves as a good substitute for ThF4 when high damage thresholds are required. Provides an absorption value close to ThF4 and is harder and more durable.	Is the least stressful in thick layers of the three materials but is the least durable. Has a low index and lower absorption at wavelengths greater than 12 µm. Produces low outgassing and spitting.	Has the highest index of refraction of the three alternate compounds. Provides a barrier to moisture because of its dense microstructure. Possesses low scatter and good abrasion resistance. Yields a protective layer on softer materials such as IRBTM and other materials. Produces the hardest, most impermeable layers.

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Forms and Sizes Available

Item No.	Purity	Description
YF3  Y-1049	99.9%	3-12 mm melted pieces
IRBTM  I-3005  I-3006	99.9%  99.9%	1-3 mm melted pieces  3-6 mm melted pieces
IRXTM  I-3000  I-3001	99.9%  99.9%	1-3 mm melted pieces  3-6 mm melted pieces

ThF₄ is available in various qualities and particle sizes, depending upon the application. Please visit our online catalog to browse our stock items or contact CERAC's customer service department for more information.

Technical Assistance
Please contact our sales department via e-mail or by phone at 414-289-9800 for application assistance or for other technical concerns regarding the use of these fluorine coating materials.

Other Coating Materials
CERAC manufactures one of the world's largest selections of coating materials and can produce nearly any desired non-standard coating material. Numerous materials for evaporation as well as sputtering targets of various compositions can be found on our on-line catalog. If you require a custom manufactured item, please contact our sales department at 414-289-9800 or sales@cerac.com with your specific requirements. You can also fill out our quotation request form.

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Comparisons Between Thorium Fluoride and Replacement Materials

Property	ThF4	YF3	IRBTM	IRXTM
Absorption at 10.6   µm for QW (%)1	0.06	0.12	0.43	0.8
Trans. Loss at: (%) 12 µm 13 µm	<2 ~4	6 <10	<3 ~4	<10 <15
Index 10-12 µm	1.35	1.35-1.3	1.35-1.30	1.43-1.40
Durability Solubility Humidity Abrasion	Sl. sol. Some effect Soft	Insol. Low susceptibility Rel. hard	Sl. sol. Some effect Soft	Insol. No effect Hardest
Adhesion & Stress Thickness Limit (µm)	~2.5 (ZnS)	2 (ZnS)	>2.5 (ZnS & Ge)	1.5 (ZnS) 2 (Ge)
Scatter	Moderate	Low	Low	Very Low
Evaporation Behavior Evap. Temp. (°C) Substrate Temp. (°C) Melt or Sublime	900 175 S	900 175-200 M	700 200-225 M	1000 150-225 M

1. Absolute absorption determined calorimetrically by D. Fisher and R. Compton at Coherent Auburn Group.

IRB^TM and IRX^TM are Trademarks of CERAC, inc.

Phone:  414-289-9800 /  FAX: 414-289-9805  /   ceracinfo@beminc.com