Zinc selenide (polycrystalline optical material) ZnSe

spore: profile
id: zinc-selenide
spore_version: 0.2
family: optical-crystals
name: Zinc selenide (polycrystalline optical material)
abbreviation: ZnSe
role: infrared optical window and lens for CO2 lasers at 10.6 µm
category: glasses-optics
type: optical-crystals
summary: |
  Zinc selenide is a zinc and selenium compound with a cubic zinc blende structure. The optical grade is polycrystalline. Crystran says it is produced from zinc vapour and hydrogen selenide gas, forming as sheets on graphite susceptors. Crystran gives a transmission range of 0.6 to 21 µm and a refractive index of 2.4028 at 10.6 µm, where two uncoated surfaces reflect 29.1% of the light. LASER COMPONENTS calls it the standard material for CO2 laser lenses and windows, with about 70% transmission uncoated. The material is soft, with a Knoop hardness of 120 and a rupture modulus of 55.1 MPa. Its supplier safety sheet classes it as toxic if swallowed or inhaled, and it should not be used above 250 °C in normal air.
best_for: Lenses and windows that must pass 10.6 µm CO2 laser light with very low absorption, and infrared windows that need transmission out to about 21 µm
weakest_at: 'Softness and toxicity: Knoop hardness of 120 and a rupture modulus of 55.1 MPa (Crystran and Coherent), and a supplier safety sheet that lists it as toxic if swallowed or inhaled (Angstrom Sciences)'
identity:
  formula: ZnSe
  cas: 1315-09-9
  crystal_system: cubic zinc blende (Crystran); a hexagonal wurtzite polymorph also exists (Wikipedia)
  space_group: F43m
  source: crystran-znse
  where: Product Data table, Class/Structure row (FCC Cubic, F43m (#216), Zinc Blende structure, polycrystalline); CAS 1315-09-9 from the Wikipedia infobox and Angstrom Sciences SDS section 1
tags:
  environments:
    - low-earth-orbit
  stresses: []
  applications:
    - optics-and-cameras
    - electronics-and-chips
properties:
  - benchmark: density
    label: Density at 300 K (manufacturer)
    value: 5.27
    unit: g/cm3
    scope: material
    conditions:
      temperature: 300 K
    method: Value printed as Density @ 300 K in the Tydex CVD zinc selenide table
    status: ground
    source: tydex-cvd-znse
    where: Density @ 300 K line
  - benchmark: density
    label: Density (supplier safety sheet)
    value: 5.42
    unit: g/cc
    scope: material
    conditions:
      basis: temperature not stated
    method: Value printed in the Angstrom Sciences SDS. It differs from the manufacturer figure of 5.27 g/cm3 and both are kept
    status: ground
    source: angstrom-znse-sds
    where: Section 9, Density row
  - benchmark: melting_point
    label: Melting point
    value: 1525
    unit: °C
    scope: material
    conditions:
      basis: value as printed, no test condition given
    method: Printed in the Crystran Product Data table; the row points to notes that were not found in the page text
    status: ground
    source: crystran-znse
    where: Product Data table, Melting Point row
  - benchmark: refractive_index
    label: Refractive index at 10.6 µm
    value: 2.4028
    unit: '-'
    scope: material
    conditions:
      wavelength: 10.6 µm
    method: Printed in the Crystran Product Data table; Tydex prints the same 2.4028 at 10.6 µm
    status: ground
    source: crystran-znse
    where: Product Data table, Refractive Index row (2.4028 at 10.6 µm)
  - benchmark: transmission_range
    label: Transmission range, uncoated
    value: 0.6
    value_high: 21
    bound: range
    unit: µm
    scope: material
    conditions:
      basis: uncoated optical material; thickness not stated
    method: Printed as a range in the Crystran Product Data table. The Tydex page prints 0.5 to 19 with a unit that is probably a typo, so it is not used
    status: ground
    source: crystran-znse
    where: Product Data table, Transmission Range row
  - benchmark: absorption_coefficient
    label: Bulk absorption at 10.6 µm
    value: 0.0005
    unit: cm-1
    scope: material
    conditions:
      wavelength: 10.6 µm
      bound: less than, as printed
      temperature: 20 °C
    method: Coherent prints a bulk absorption coefficient of less than 0.0005 cm-1 at 10.6 µm in its ZnSe material properties table
    status: ground
    source: coherent-znse
    where: ZnSe Material Properties (at 20 °C), Bulk Absorption Coefficient row
  - benchmark: reflection_loss
    label: Reflection loss, two uncoated surfaces
    value: 29.1
    unit: '%'
    scope: material
    conditions:
      wavelength: 10.6 µm
      surfaces: two uncoated surfaces
    method: Printed in the Crystran Product Data table
    status: ground
    source: crystran-znse
    where: Product Data table, Reflection Loss row
  - benchmark: thermal_conductivity
    label: Thermal conductivity
    value: 18
    unit: W m-1 K-1
    scope: material
    conditions:
      temperature: 298 K
    method: Printed in the Crystran Product Data table
    status: ground
    source: crystran-znse
    where: Product Data table, Thermal Conductivity row
  - benchmark: specific_heat
    label: Specific heat capacity
    value: 0.339
    unit: J/(g K)
    scope: material
    conditions:
      temperature: 298 K
    method: Printed as heat capacity in the Tydex CVD zinc selenide table
    status: ground
    source: tydex-cvd-znse
    where: Heat capacity @ 298 K line
  - benchmark: cte
    label: Linear thermal expansion at 273 K
    value: 7.1
    unit: x10-6/K
    scope: material
    conditions:
      temperature: 273 K
    method: Printed as thermal expansion in the Tydex table; Crystran prints 7.1 x 10-6/°C at 273 K
    status: ground
    source: tydex-cvd-znse
    where: Thermal expansion (1/K) line, @ 273 K
  - benchmark: cte
    label: Linear thermal expansion at 473 K
    value: 8.3
    unit: x10-6/K
    scope: material
    conditions:
      temperature: 473 K
    method: Printed as thermal expansion in the Tydex table; it rises with temperature (7.8 at 373 K)
    status: ground
    source: tydex-cvd-znse
    where: Thermal expansion (1/K) line, @ 473 K
  - benchmark: cte
    label: Linear expansion coefficient at 20 °C
    value: 7.57
    unit: x10-6/°C
    scope: material
    conditions:
      temperature: 20 °C
    method: Printed in the Coherent ZnSe material properties table
    status: ground
    source: coherent-znse
    where: Linear Expansion Coefficient row, @ 20 °C
  - benchmark: elastic_modulus
    label: Young's modulus
    value: 67.2
    unit: GPa
    scope: material
    conditions:
      form: polycrystalline optical grade, as printed
    method: Printed in the Crystran Product Data table (9.75 x 10^6 psi in the Coherent table)
    status: ground
    source: crystran-znse
    where: Product Data table, Youngs Modulus (E) row
  - benchmark: poissons_ratio
    label: Poisson's ratio
    value: 0.28
    unit: '-'
    scope: material
    conditions:
      basis: dimensionless
    method: Printed in the Crystran Product Data table
    status: ground
    source: crystran-znse
    where: Product Data table, Poisson Ratio row
  - benchmark: bulk_modulus
    label: Bulk modulus
    value: 40
    unit: GPa
    scope: material
    conditions:
      basis: as printed
    method: Printed in the Crystran Product Data table
    status: ground
    source: crystran-znse
    where: Product Data table, Bulk Modulus (K) row
  - benchmark: flexural_strength
    label: Rupture modulus (apparent elastic limit)
    value: 55.1
    unit: MPa
    scope: material
    conditions:
      grain_size: under 100 µm (Coherent)
      note: Coherent calls this rupture modulus; Crystran prints the same 55.1 MPa as apparent elastic limit
    method: Printed in the Coherent ZnSe material properties table as 55.1 MPa (8,000 psi)
    status: ground
    source: coherent-znse
    where: Rupture Modulus row
  - benchmark: knoop_hardness
    label: Knoop hardness
    value: 105
    value_high: 120
    bound: range
    unit: kg/mm2
    scope: material
    conditions:
      temperature: 20 °C
      note: range as printed; Crystran prints 120 with a 500 g indenter
    method: Printed as a range in the Coherent ZnSe material properties table
    status: ground
    source: coherent-znse
    where: Knoop Hardness row
  - benchmark: thermo_optic_coefficient
    label: Thermo-optic coefficient dn/dT at 10.6 µm
    value: 6.1
    unit: x10-5/°C
    scope: material
    conditions:
      wavelength: 10.6 µm
    method: Printed in the Coherent ZnSe material properties table
    status: ground
    source: coherent-znse
    where: Thermo-Optic Coefficient (dn/dT) row
  - benchmark: water_solubility
    label: Solubility in water
    value: 0.001
    unit: g/100 g water
    scope: material
    conditions:
      temperature: not stated
    method: Printed in the Crystran Product Data table; the Angstrom SDS calls it insoluble
    status: ground
    source: crystran-znse
    where: Product Data table, Solubility row
  - benchmark: band_gap
    label: Band gap at 25 °C
    value: 2.7
    unit: eV
    scope: material
    conditions:
      temperature: 25 °C
    method: Stated in the Wikipedia article text; the article infobox gives 2.82 eV at 10 K
    status: ground
    source: wikipedia-znse
    where: Article text, band gap paragraph
  - benchmark: max_service_temp
    label: Maximum window temperature in air
    value: 250
    unit: °C
    scope: material
    conditions:
      atmosphere: normal atmosphere
    method: Stated as a safety limit for windows in the Crystran product text, not in the table
    status: ground
    source: crystran-znse
    where: Product text, safety note on window temperature
corrosion:
  - environment: Air at high temperature
    headline: Oxidizes significantly at 300 °C. Windows should not go above 250 °C in normal atmosphere.
    effect: Crystran says ZnSe oxidizes significantly at 300 °C, shows plastic deformation at about 500 °C and dissociates at about 700 °C. Its safety advice is not to use windows above 250 °C in normal atmosphere.
    rating: moderate
    conditions:
      atmosphere: normal air, as stated
      exposure: temperature limits only; exposure time not stated
    source: crystran-znse
    where: Product text, thermal limits paragraph
  - environment: Atomic oxygen (simulated by an oxygen plasma, as in low Earth orbit)
    headline: An oxygen plasma equal to about 16 years in low Earth orbit changed the mid-infrared response very little.
    effect: Thin ZnSe films were exposed to an electron cyclotron resonance oxygen plasma, equal to about 16 years in low Earth orbit. The mid-infrared optical response barely changed, while the ultraviolet to near-infrared response changed a lot. The authors attribute the oxidation to a thin surface layer.
    rating: low
    conditions:
      basis: thin films, not bulk optics
      fluence: about 16 years in low Earth orbit equivalent
    source: yan2002
    where: Abstract (repository copy)
  - environment: Water
    headline: Very low solubility, at 0.001 g per 100 g of water.
    effect: Crystran prints a solubility of 0.001 g/100 g water. The Angstrom Sciences SDS calls the material insoluble in water. Neither source reports a humidity or ageing test.
    rating: low
    conditions:
      temperature: not stated
    source: crystran-znse
    where: Product Data table, Solubility row
  - environment: Bases and oxidizing agents, or a fire
    headline: Incompatible with bases and oxidizers. Heating in a fire gives hydrogen selenide and selenium dioxide.
    effect: The Angstrom Sciences SDS lists bases and oxidizing agents as materials to avoid. Its decomposition products are hydrogen selenide, selenium dioxide and metal oxide fume.
    rating: moderate
    conditions:
      basis: SDS reactivity and decomposition statements
    source: angstrom-znse-sds
    where: Section 10 (Stability and reactivity)
risks:
  hazards:
    - text: 'Signal word Danger. H301 and H331: toxic if swallowed or inhaled. H373: may cause damage to organs through prolonged or repeated exposure. Precautionary statements include P270 (do not eat, drink or smoke when using) and P310 (call a Poison Center or doctor).'
      ghs:
        - H301
        - H331
        - H373
      source: angstrom-znse-sds
      where: Section 2 (Hazard identification)
    - text: The Wikipedia infobox also lists H410 with pictograms GHS06, GHS08 and GHS09. The Angstrom SDS does not print H410, though its section 12 rates aquatic toxicity as High.
      ghs:
        - H410
      source: wikipedia-znse
      where: Infobox (hazard statements)
    - text: Exposure limit of 0.2 mg/m3 as Se, long-term value. The SDS calls for a dust respirator, rubber gloves and safety glasses or goggles, with ventilation to keep concentrations at or below the limit.
      ghs: []
      source: angstrom-znse-sds
      where: Sections 7 and 8
    - text: The SDS lists chronic selenium effects, including fatigue, loss of fingernails and hair, anaemia and weight loss.
      ghs: []
      source: angstrom-znse-sds
      where: Section 11 (Toxicological information)
  failure_risks:
    - mode: Overheating a window in normal air
      trigger: Use above 250 °C in normal atmosphere (Crystran)
      consequence: Oxidation becomes significant at 300 °C, plastic deformation starts at about 500 °C and dissociation at about 700 °C (Crystran).
      severity: moderate
      source: crystran-znse
      where: Product text, thermal limits paragraph
    - mode: Surface damage or fracture under mechanical load
      trigger: Contact with hard particles, clamping loads or handling
      consequence: Knoop hardness is 105 to 120 kg/mm2 and the rupture modulus is 55.1 MPa (Coherent), so the surface marks easily and a stressed part can break at a low load.
      severity: moderate
      source: coherent-znse
      where: Knoop Hardness and Rupture Modulus rows
    - mode: Toxic dust or fume from machining or a fire
      trigger: Grinding, cutting or spilling the powder, or a fire near the part
      consequence: Dust raises selenium exposure. In a fire it gives hydrogen selenide, selenium dioxide and metal oxide fume (Angstrom Sciences).
      severity: high
      source: angstrom-znse-sds
      where: Sections 6, 8 and 10
  side_effects:
    - text: Machining and spills make dust. The SDS says take care not to raise dust, not to blow dust off clothing or skin with compressed air, and to wash thoroughly after handling.
      affects: People working near machining or spills, and the work area
      source: angstrom-znse-sds
      where: Sections 6 and 7
  handling:
    - text: Handle under dry protective gas, wash thoroughly after handling and do not use food or tobacco in the work area (Angstrom SDS section 7).
      source: angstrom-znse-sds
      where: Section 7 (Handling and storage)
    - text: Store in a cool, dry place in a tightly sealed container, apart from bases and oxidizing agents.
      source: angstrom-znse-sds
      where: Section 7 and section 10
    - text: Clean up spills by vacuuming with a HEPA filter into a closed container. Take care not to raise dust.
      source: angstrom-znse-sds
      where: Section 6 (Accidental release measures)
  mitigations:
    - text: Keep windows at or below 250 °C in normal atmosphere, and use a dust respirator, gloves and eye protection when handling the powder or machining.
      source: crystran-znse
      where: Product text (window temperature); SDS section 8
uses:
  - application: optics-and-cameras
    device: CO2 laser lenses and output windows at 10.6 µm
    example: LASER COMPONENTS calls zinc selenide the standard material for CO2 laser lenses and windows. Uncoated, about 70% of 10.6 µm light passes through; coating both sides raises transmission above 99.4%.
    source: lc-co2-optics
    where: Materials for CO2 laser optics, pages 1 and 2
  - application: optics-and-cameras
    device: Infrared optical coating for low Earth orbit (ground test only)
    example: A ground test exposed thin ZnSe films to an oxygen plasma equal to about 16 years in low Earth orbit. The mid-infrared optical response barely changed, and the authors judged ZnSe potentially suitable for space infrared applications.
    source: yan2002
    where: Abstract (repository copy)
  - application: electronics-and-chips
    device: X-ray and gamma-ray detectors (tellurium-activated ZnSe scintillator)
    example: Tellurium-activated ZnSe is a scintillator with an emission peak at 640 nm, used in x-ray and gamma-ray detectors.
    source: wikipedia-znse
    where: Article text, uses paragraph
supply:
  - subject: Zinc
    producers:
      - country: China
        share_percent: 31.5
        year: 2025
      - country: Peru
        share_percent: 11.5
        year: 2025
      - country: Australia
        share_percent: 8.5
        year: 2025
      - country: Mexico
        share_percent: 6
        year: 2025
      - country: United States
        share_percent: 5.2
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (zinc named)
        listed: true
      - list: EU critical raw materials list (34 CRMs, under Regulation (EU) 2024/1252); zinc not named
        listed: false
    recycling: 'USGS: US refined zinc is partly recovered from secondary materials, including galvanizing residues and crude zinc oxide.'
    substitutes: []
    source: usgs-mcs2026-zinc
    where: World Mine Production and Reserves table (2025e; shares calculated by Space Mushroom against the 13,000 thousand t world total, which is rounded); Recycling. Critical list from the USGS 2025 list page and the EU page.
  - subject: Selenium
    abundance: 0.05 ppm in the Earth's crust (USGS PP 1802-A, Table A1)
    producers:
      - country: China
        share_percent: 52.6
        year: 2025
      - country: Japan
        share_percent: 16.8
        year: 2025
      - country: Russia
        share_percent: 8.4
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (selenium not named)
        listed: false
      - list: EU critical raw materials list (selenium not named)
        listed: false
    recycling: 'USGS: recycling is insignificant. Most scrap from electronic materials is exported for recovery of its selenium.'
    substitutes:
      - LASER COMPONENTS also offers CO2 laser optics in germanium and gallium arsenide on request (supplier page, not a substitute the source ranks).
    source: usgs-mcs2026-selenium
    where: Refinery production table, 2025 column (world total 3,800 t, selenium content; shares calculated by Space Mushroom. USGS states China at 53%); Recycling; Substitutes. Abundance from USGS PP 1802-A Table A1; critical lists from the USGS 2025 list and the EU page.
media: []
documents:
  - title: 'Angstrom Sciences safety data sheet: Zinc Selenide (CAS 1315-09-9), last revised 07/07/15'
    type: sds
    url: https://angstromsciences.com/wp-content/uploads/files/SDS/Zinc%20Selenide.pdf
    year: 2015
  - title: 'Crystran: Zinc Selenide (ZnSe) product data'
    type: datasheet
    url: https://www.crystran.co.uk/optical-materials/zinc-selenide-znse
    year: 2026
  - title: 'Coherent: ZnSe material properties (bulk optical materials)'
    type: datasheet
    url: https://www.coherent.com/optics/crystals/bulk-optical-materials/zinc-selenide
    year: 2026
  - title: 'Tydex: CVD zinc selenide properties'
    type: datasheet
    url: https://tydexoptics.com/materials1/for_transmission_optics/cvd_znse
    year: 2026
  - title: 'LASER COMPONENTS: Materials for CO2 laser optics (12/25 edition)'
    type: datasheet
    url: https://www.lasercomponents.com/fileadmin/user_upload/home/Datasheets/diverse-laser-optics/co2-laseroptics/materials-co2-laser-optics.pdf
    year: 2025
  - title: Oxygen plasma effects on optical properties of ZnSe films (J. Vac. Sci. Technol. A, 2002)
    type: paper
    url: https://digitalcommons.unl.edu/electricalengineeringfacpub/9
    year: 2002
  - title: 'USGS Mineral Commodity Summaries 2026: Zinc'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zinc.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Selenium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-selenium.pdf
    year: 2026
  - title: USGS Professional Paper 1802-A, Table A1 (crustal abundance)
    type: report
    url: https://pubs.usgs.gov/pp/1802/a/pp1802a.pdf
    year: 2017
gaps:
  - No flight or space-qualification result for ZnSe optics was found. The only space-related source is a ground test of thin films in an oxygen plasma, which gives no data for bulk windows in orbit.
  - No radiation, proton or UV-dose result for bulk ZnSe was read in this run.
  - The Crystran safety sheet URL returned 404, so the Crystran hazard list was not read. The H-codes come from the Angstrom Sciences SDS and the Wikipedia infobox, which disagree on H410.
  - PubChem could not be opened (challenge page and REST 404), so no PubChem GHS summary is used.
  - The Thorlabs and KEMET safety sheets could not be downloaded in this run.
  - No open-access review of the CVD production route was found. The process description rests on one supplier page (Crystran) and one older description in Wikipedia (not CVD).
  - 'Single-crystal ZnSe absorption: Crystran says it is reported to be lower, but gives no figure and does not say it is available.'
  - 'Zinc crustal abundance was not found: the zinc row was not located in the USGS PP 1802-A Table A1 text read in this run.'
  - No humidity or long-term ageing test on bulk ZnSe was found.
  - Atomic weights of zinc and selenium were not read, so the recipe gives the molecular weight only.
  - No photographs were collected for this profile, so the media list is empty.
  - Sources conflict on density (5.27 and 5.42 g/cm3) and on melting point (Crystran 1525 °C; Angstrom gives more than 1100 °C, not used). Both values are kept with their sources.
sources:
  crystran-znse:
    title: 'Zinc Selenide (ZnSe): Crystran product data (Product Data table, safety notes)'
    id: Crystran product page (undated; read 2026-10-26)
    url: https://www.crystran.co.uk/optical-materials/zinc-selenide-znse
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  wikipedia-znse:
    title: 'Zinc selenide (Wikipedia article: formula, CAS, structure, band gap, uses, synthesis, hazard infobox)'
    id: Wikipedia (undated; read 2026-10-26)
    url: https://en.wikipedia.org/wiki/Zinc_selenide
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (Wikipedia)
  coherent-znse:
    title: 'Coherent: ZnSe material properties (ZnSe Material Properties table at 20 °C)'
    id: Coherent bulk optical materials page (undated; read 2026-10-26)
    url: https://www.coherent.com/optics/crystals/bulk-optical-materials/zinc-selenide
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  tydex-cvd-znse:
    title: 'Tydex: Zinc Selenide (CVD-ZnSe) properties'
    id: Tydex optics materials page (undated; read 2026-10-26)
    url: https://tydexoptics.com/materials1/for_transmission_optics/cvd_znse
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  lc-co2-optics:
    title: 'LASER COMPONENTS: Materials for CO2 laser optics'
    id: 12/25 V3 supplier PDF
    url: https://www.lasercomponents.com/fileadmin/user_upload/home/Datasheets/diverse-laser-optics/co2-laseroptics/materials-co2-laser-optics.pdf
    year: 2025
    kind: datasheet
    license: supplier document, linked not reproduced
  angstrom-znse-sds:
    title: 'Zinc Selenide: Safety Data Sheet (Angstrom Sciences, Inc.)'
    id: CAS 1315-09-9; EC 215-259-7; last revised 07/07/15
    url: https://angstromsciences.com/wp-content/uploads/files/SDS/Zinc%20Selenide.pdf
    year: 2015
    kind: datasheet
    license: supplier document, linked not reproduced
  yan2002:
    title: Oxygen plasma effects on optical properties of ZnSe films
    id: J. Vac. Sci. Technol. A 20(3), May-June 2002 (repository copy, University of Nebraska-Lincoln Digital Commons)
    url: https://digitalcommons.unl.edu/electricalengineeringfacpub/9
    year: 2002
    kind: paper
    license: repository copy, read from the abstract page
  usgs-mcs2026-zinc:
    title: Mineral Commodity Summaries 2026, Zinc
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zinc.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-selenium:
    title: Mineral Commodity Summaries 2026, Selenium
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-selenium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-pp1802a:
    title: Critical Mineral Resources of the United States - An Introduction (Professional Paper 1802-A), Table A1, crustal abundances
    id: USGS PP 1802-A
    url: https://pubs.usgs.gov/pp/1802/a/pp1802a.pdf
    year: 2017
    kind: report
    license: public domain (USGS)
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS, final list of 60 minerals)
    id: Final 2025 List of Critical Minerals, November 2025
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  ec-crm:
    title: Critical raw materials (European Commission, list of 34 critical raw materials under Regulation (EU) 2024/1252)
    id: Regulation (EU) 2024/1252
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    year: 2024
    kind: web
    license: European Commission web page
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 21
  unreachable: 4
  caveats: 3
  note: 'Written by an AI assistant on 2026-10-26 from pages and PDFs read in the same run. Unreachable: the Crystran safety sheet (404), PubChem, the Thorlabs sheet and the KEMET sheet. Caveats: density and melting point differ between suppliers; the Tydex page prints a transmission range in mm that looks like a typo, so it was not used; no open-access review of CVD production was found.'
story:
  recipe:
    line: 'ZnSe is a 1:1 compound of zinc and selenium (one atom of each per formula unit). Crystran says it is produced from zinc vapour and hydrogen selenide gas, forming as sheets on graphite susceptors. Wikipedia also lists older routes: reaction of aqueous zinc sulfate with hydrogen selenide, heating zinc oxide, zinc sulfide and selenium together, and melt growth under argon pressure.'
    parts:
      - name: Zinc
        symbol: Zn
        role: Cation in the zinc blende lattice. In the deposition route it is supplied as zinc vapour (Crystran).
      - name: Selenium
        symbol: Se
        role: Anion in the zinc blende lattice. In the deposition route it is supplied as hydrogen selenide gas (Crystran).
  risk_groups:
    - title: For people
      level: 0
      verdict: Toxic if swallowed or inhaled
      lead: The supplier safety sheet classes zinc selenide as toxic, so dust and fume need controlling. It gives a long-term exposure limit of 0.2 mg/m3 as selenium.
      points:
        - label: The powder
          line: The Angstrom Sciences sheet has the signal word Danger, with H301 and H331 (toxic if swallowed or inhaled) and H373 (may cause damage to organs through prolonged or repeated exposure).
        - label: Dust
          line: The sheet says to take care not to raise dust, to vacuum spills with a HEPA filter, and not to blow dust off with compressed air.
        - label: In a fire
          line: The decomposition products are hydrogen selenide, selenium dioxide and metal oxide fume.
    - title: If the optic overheats
      lead: These limits come from the supplier's product text, not from incident data.
      points:
        - label: Window limit
          line: Crystran says windows should not be used above 250 °C in normal atmosphere. Oxidation becomes significant at 300 °C, plastic deformation starts at about 500 °C, and dissociation at about 700 °C.
    - title: Handling and storage
      points:
        - label: Storage
          line: Store in a cool, dry place in a tightly sealed container, apart from bases and oxidizing agents.
        - label: Protection
          line: The sheet calls for a dust respirator, rubber gloves, and safety glasses or goggles.
  why: Zinc selenide is a zinc and selenium compound that transmits infrared light from about 0.6 µm to 21 µm (Crystran). That range includes the 10.6 µm line of CO2 lasers. Its refractive index is 2.4028 at 10.6 µm, and its absorption there is very low, less than 0.0005 cm-1 (Coherent). The material is used for CO2 laser lenses and windows for these reasons. Its hardness and strength are modest, and its selenium content is toxic, so handling and temperature limits matter.
  uses:
    - where: CO2 laser optics
      line: LASER COMPONENTS calls zinc selenide the standard material for CO2 laser lenses and windows. Uncoated, about 70% of 10.6 µm light passes through, and coating both sides raises transmission above 99.4%.
    - where: Infrared optics for space (ground test)
      line: A ground test exposed thin ZnSe films to an oxygen plasma equal to about 16 years in low Earth orbit. The mid-infrared optical response barely changed, and the authors judged ZnSe potentially suitable for space infrared applications.
    - where: X-ray and gamma-ray detectors
      line: Tellurium-activated ZnSe is a scintillator with an emission peak at 640 nm, used in x-ray and gamma-ray detectors (Wikipedia).
  can_do:
    - label: Infrared transmission
      benchmark: transmission_range
      value: 0.6 to 21 µm
      line: Crystran gives an uncoated transmission range of 0.6 to 21 µm, which covers the 10.6 µm line of CO2 lasers.
    - label: Transmission at 10.6 µm
      benchmark: reflection_loss
      value: about 70% uncoated
      line: LASER COMPONENTS prints about 70% transmission at 10.6 µm for uncoated material. This is close to the 29.1% reflection loss from two uncoated surfaces that Crystran gives.
    - label: Absorption
      benchmark: absorption_coefficient
      value: less than 0.0005 cm-1 at 10.6 µm
      line: Coherent prints the bulk absorption at 10.6 µm as less than 0.0005 cm-1. LASER COMPONENTS calls its laser-grade ZnSe suited to high-power applications.
    - label: Temperature limit
      benchmark: max_service_temp
      value: 250 °C in normal atmosphere
      line: Crystran advises against using ZnSe windows above 250 °C in normal atmosphere.
  compare: Against sapphire, the other optical crystal in this collection, zinc selenide transmits further into the infrared, to 21 µm (Crystran), and it is much softer, with a Knoop hardness of 120 kg/mm2 (Crystran). The sapphire record is built on different tests and units, so the two are not compared number by number here. The sources read give no cost or availability comparison.
  compare_rows:
    - label: Transmission range
      benchmark: transmission_range
    - label: Refractive index
      benchmark: refractive_index
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  handling:
    - Handle under dry protective gas and wash thoroughly after handling, as the safety sheet directs.
    - Store in a cool, dry place in a tightly sealed container, away from bases and oxidizing agents.
    - Vacuum spills with a HEPA filter and avoid raising dust. Do not blow dust off with compressed air.
    - Keep windows at or below 250 °C in normal atmosphere.
  good_for:
    - Low-absorption CO2 laser optics. Uncoated transmission is about 70% at 10.6 µm, and two-side coating raises it above 99.4% (LASER COMPONENTS).
    - Long-wave infrared windows. The uncoated transmission range runs from 0.6 to 21 µm (Crystran).
  watch_out:
    - Softness. Knoop hardness is 105 to 120 kg/mm2 (Coherent), so the surface marks easily.
    - Toxicity. The safety sheet classes the material as toxic if swallowed or inhaled, with H373 for repeated exposure.
    - Temperature. Do not use windows above 250 °C in normal atmosphere (Crystran).
  verdict: Zinc selenide is the standard low-absorption material for CO2 laser optics and an infrared window out to about 21 µm. It is soft, its selenium content is toxic, and it should not run above 250 °C in air, so it suits protected optics better than hard-wearing windows.