# Cadmium sulfide

**Cadmium sulfide** (CdS) is an inorganic compound of cadmium and sulfur, a yellow to orange crystalline solid that is both a widely used artist's pigment (cadmium yellow) and an important II-VI semiconductor with a direct band gap of 2.42 eV at 300 K.<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/cadmium%20sulfide)</sup><sup> • </sup><sup>[2](https://www.sciencedirect.com/topics/chemical-engineering/cadmium-sulfide)</sup> It is classified as carcinogenic to humans, and its handling is governed by strict occupational exposure limits.<sup>[3](https://www.fishersci.com/store/msds?countryCode=US&language=en&partNumber=AA4545530&productDescription=CADMIUM+SULFIDE+250G&vendorId=VN00024248)</sup>

| Key fact | Detail |
|---|---|
| Formula and mass | CdS; molecular weight 144.48 g/mol; CAS 1306-23-6<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/cadmium%20sulfide)</sup> |
| Appearance | Light yellow or orange crystals, or yellow-to-brown powder<sup>[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0404&p_lang=en&p_version=1)</sup> |
| Physical constants | Density 4.8 g/cm³; sublimation point 980 °C; insoluble in water<sup>[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0404&p_lang=en&p_version=1)</sup> |
| Band gap | Direct gap of 2.42 eV at 300 K (2.52 eV at 77 K, 2.582 eV at 4.2 K)<sup>[2](https://www.sciencedirect.com/topics/chemical-engineering/cadmium-sulfide)</sup><sup> • </sup><sup>[5](https://etheses.durham.ac.uk/id/eprint/8867/1/8867_5798.PDF?UkUDh%3ACyT=)</sup> |
| Crystal structures | Hexagonal wurtzite and cubic zinc blende<sup>[6](https://pubs.rsc.org/en/content/articlepdf/2024/ta/d4ta03496a)</sup> |
| Natural occurrence | The mineral greenockite (IMA symbol Gnk)<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/cadmium%20sulfide)</sup> |
| Carcinogen classification | IARC Group 1, carcinogenic to humans; NTP "known"<sup>[3](https://www.fishersci.com/store/msds?countryCode=US&language=en&partNumber=AA4545530&productDescription=CADMIUM+SULFIDE+250G&vendorId=VN00024248)</sup> |
| Main uses | Pigments, solar cells, smoke and radiation detectors, LEDs, photomultipliers, photoconductors<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/cadmium%20sulfide)</sup> |

## Chemistry and physical properties

Cadmium sulfide is an n-type semiconductor that can be polished like a metal.<sup>[7](https://pubchem.ncbi.nlm.nih.gov/compound/1306-23-6)</sup> It is essentially insoluble in water but dissolves in concentrated or warm dilute mineral acids with evolution of hydrogen sulfide gas, and it is readily decomposed by moderately dilute nitric acid.<sup>[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0404&p_lang=en&p_version=1)</sup><sup> • </sup><sup>[7](https://pubchem.ncbi.nlm.nih.gov/compound/1306-23-6)</sup> Its refractive index is high, about 2.506 and 2.529 for the two principal directions, which is one reason the pigment particles scatter light strongly.<sup>[7](https://pubchem.ncbi.nlm.nih.gov/compound/1306-23-6)</sup>

**Thermal behavior.** On heating in air to 700 °C, especially with moisture present, CdS is oxidized to the sulfate, basic sulfate, and eventually the oxide; it sublimes at 980 °C without melting at atmospheric pressure.<sup>[7](https://pubchem.ncbi.nlm.nih.gov/compound/1306-23-6)</sup> Heating to decomposition emits very toxic fumes of cadmium and sulfur oxides, and welding or soldering of cadmium sulfide-treated surfaces releases highly toxic cadmium oxide.<sup>[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0404&p_lang=en&p_version=1)</sup><sup> • </sup><sup>[7](https://pubchem.ncbi.nlm.nih.gov/compound/1306-23-6)</sup> The cubic form (beta-CdS) can be transformed to the hexagonal alpha form by heating at 750 °C in a sulfur atmosphere.<sup>[7](https://pubchem.ncbi.nlm.nih.gov/compound/1306-23-6)</sup>

## Crystal structure

CdS crystallizes in two structures, hexagonal wurtzite and cubic zinc blende, and a 2024 review in the *Journal of Materials Chemistry A* examines the synthesis, electronic and optical behavior, and applications of each phase separately.<sup>[6](https://pubs.rsc.org/en/content/articlepdf/2024/ta/d4ta03496a)</sup> The wurtzite structure is the normal form of the compound.<sup>[5](https://etheses.durham.ac.uk/id/eprint/8867/1/8867_5798.PDF?UkUDh%3ACyT=)</sup> The two phases differ slightly in density, 4.82 g/cm³ for the hexagonal form versus 4.50 g/cm³ for the cubic form.<sup>[7](https://pubchem.ncbi.nlm.nih.gov/compound/1306-23-6)</sup>

The band edges of wurtzite CdS lie at the same point, k = 0, in the [Brillouin zone](https://www.edgepedia.org/brillouin-zone), so the gap is direct; accepted values are 2.43 eV at room temperature, 2.52 eV at liquid-nitrogen temperature, and 2.582 eV at liquid-helium temperature.<sup>[5](https://etheses.durham.ac.uk/id/eprint/8867/1/8867_5798.PDF?UkUDh%3ACyT=)</sup> Polycrystalline CdS thin films show a direct gap of 2.42 to 2.45 eV at room temperature.<sup>[8](https://www.sciencedirect.com/science/article/abs/pii/S0040609001008306)</sup>

## As a pigment: cadmium yellow

Friedrich Stromeyer discovered metallic cadmium in 1817 and synthetically prepared the yellow pigments in Germany; production was delayed until about 1840 because of the scarcity of the metal, and the pigments entered artists' paints in the mid-1840s.<sup>[9](https://cameo.mfa.org/wiki/Cadmium_yellow)</sup><sup> • </sup><sup>[10](https://www.webexhibits.org/pigments/indiv/history/cdyellow.html)</sup> The classical preparation heated an acid solution of a cadmium salt (chloride or sulfate) with hydrogen sulfide gas until a powder formed, yielding hues from lemon yellow to deep orange.<sup>[10](https://www.webexhibits.org/pigments/indiv/history/cdyellow.html)</sup> Particle size and composition vary the color from light yellow to orange.<sup>[9](https://cameo.mfa.org/wiki/Cadmium_yellow)</sup>

**Permanence and degradation.** The deeper varieties of cadmium yellow and orange were the most permanent, while paler varieties were known to fade in sunlight.<sup>[10](https://www.webexhibits.org/pigments/indiv/history/cdyellow.html)</sup> Conservation studies have documented degradation of cadmium sulfide in paintings, driven by unsuitable storage, unfavorable environmental conditions, and the intrinsic photo-reactivity of the pigment, which is sensitive to crystallite and grain size.<sup>[11](https://journals.ub.uni-heidelberg.de/index.php/conserva/article/view/110979)</sup><sup> • </sup><sup>[12](https://novaresearch.unl.pt/en/publications/an-investigation-into-the-synthesis-of-cadmium-sulfide-pigments-f/)</sup> A discolouring chemical interaction between cadmium yellow and malachite (basic copper carbonate) has been identified, consistent with the old painters' rule that cadmiums could not be mixed with copper-based pigments.<sup>[13](https://opus.lib.uts.edu.au/handle/10453/37293)</sup><sup> • </sup><sup>[10](https://www.webexhibits.org/pigments/indiv/history/cdyellow.html)</sup> In the 1920s, cadmium pigments were co-precipitated with barium sulfate to make the cheaper cadmium lithopone, and a solid solution of CdS with zinc sulfide is known as Pigment Yellow 35.<sup>[9](https://cameo.mfa.org/wiki/Cadmium_yellow)</sup>

## Optoelectronics and quantum dots

Because of its direct 2.42 eV gap, strong optical absorption, and thermal and chemical stability, CdS is used in solar cells, photodetectors, light-emitting diodes, and lasers.<sup>[2](https://www.sciencedirect.com/topics/chemical-engineering/cadmium-sulfide)</sup> Its largest photovoltaic role is as the wide-bandgap window and buffer layer in CdS/CdTe thin-film solar cells, where the CdS (2.42 eV) is typically grown by chemical bath deposition on top of the narrow-gap (1.45 eV) CdTe absorber; the glass/conducting-oxide/CdS/CdTe/metal heterostructure has been described as one of the lowest-cost efficient converters of solar radiation, at 15.8% efficiency in the cited device literature.<sup>[14](https://link.springer.com/article/10.1007/s10854-017-7615-x)</sup><sup> • </sup><sup>[8](https://www.sciencedirect.com/science/article/abs/pii/S0040609001008306)</sup> In CdTe modules the CdS layer also helps the growth and electrical properties between the transparent conducting oxide and the absorber.<sup>[15](https://www.nlr.gov/pv/cadmium-telluride-solar-cells)</sup>

**Quantum dots.** When CdS is made as nanometer-scale crystals smaller than the exciton [Bohr radius](https://www.edgepedia.org/bohr-radius), quantum confinement makes the bandgap and emission color tunable with particle size, and the dots show wide continuous absorption, narrow emission, and high photostability.<sup>[16](https://pmc.ncbi.nlm.nih.gov/articles/PMC3463453/)</sup> CdS quantum dots are studied for solar cells, LEDs, photocatalysis, and sensors.<sup>[17](https://www.sciencedirect.com/science/article/pii/B9780323852784000180)</sup> Common synthesis routes for cadmium-based dots include hot injection, co-precipitation, successive ionic layer adsorption and reaction, hydrothermal, and microwave-assisted methods.<sup>[18](https://pmc.ncbi.nlm.nih.gov/articles/PMC10488842/)</sup> Environmentally benevolent routes using plant sources and microorganisms have also been reviewed for CdS nanoparticles.<sup>[19](https://doi.org/10.1016/j.enceco.2021.06.002)</sup>

## Toxicity and handling

Cadmium sulfide is classified by IARC as Group 1, carcinogenic to humans, and by the NTP as a known human carcinogen.<sup>[3](https://www.fishersci.com/store/msds?countryCode=US&language=en&partNumber=AA4545530&productDescription=CADMIUM+SULFIDE+250G&vendorId=VN00024248)</sup> The International Chemical Safety Card states that the substance is carcinogenic to humans and that long-term or repeated exposure may affect the kidneys, bones, and respiratory tract, resulting in kidney impairment, osteoporosis, and chronic inflammation of the respiratory tract.<sup>[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0404&p_lang=en&p_version=1)</sup> The occupational exposure limits are correspondingly low: the ACGIH threshold limit value for the respirable fraction is 0.002 mg/m³ as TWA, and the EU occupational exposure limit is 0.001 mg/m³ inhalable as TWA.<sup>[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0404&p_lang=en&p_version=1)</sup> In the United States, the OSHA permissible exposure limit for all cadmium compounds, as Cd, is 0.005 mg/m³ as an 8-hour time-weighted average.<sup>[20](https://www.cdc.gov/niosh/npg/npgd0087.html)</sup>

The compound is absorbed by inhalation of its aerosol and by ingestion; short-term effects include eye irritation and cough, and powdered material can quickly reach harmful airborne concentrations.<sup>[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0404&p_lang=en&p_version=1)</sup> Because ingestion risk is limited by very low solubility, the chief hazards are dust inhalation and fumes from heating or welding.<sup>[9](https://cameo.mfa.org/wiki/Cadmium_yellow)</sup><sup> • </sup><sup>[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0404&p_lang=en&p_version=1)</sup> The chemical is persistent and should not be allowed to enter the environment; it may bioaccumulate in crustacea and plants.<sup>[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0404&p_lang=en&p_version=1)</sup>

**Toxicity of cadmium quantum dots.** In biological applications, the toxicity of cadmium-containing quantum dots raises concerns beyond the bulk compound, because of free cadmium ion release and nano-size effects; reviews propose toxicity mechanisms and design optimizations, such as surface modification, aimed at minimal cytotoxicity.<sup>[21](https://pubmed.ncbi.nlm.nih.gov/33588242/)</sup> This concern has driven interest in heavy-metal-free alternatives such as indium phosphide, copper indium sulfide, and graphene quantum dots.<sup>[22](https://link.springer.com/article/10.1186/s11671-025-04323-6)</sup>

## References

1. [Cadmium Sulfide, CID 14783, PubChem (NCBI)](https://pubchem.ncbi.nlm.nih.gov/compound/cadmium%20sulfide)
2. [Cadmium Sulfide, an overview, ScienceDirect Topics](https://www.sciencedirect.com/topics/chemical-engineering/cadmium-sulfide)
3. [Safety Data Sheet, Cadmium Sulfide, Fisher Scientific](https://www.fishersci.com/store/msds?countryCode=US&language=en&partNumber=AA4545530&productDescription=CADMIUM+SULFIDE+250G&vendorId=VN00024248)
4. [ICSC 0404, Cadmium Sulfide, ILO/WHO International Chemical Safety Card](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0404&p_lang=en&p_version=1)
5. [Exciton spectra and band structure of CdS, Durham University thesis](https://etheses.durham.ac.uk/id/eprint/8867/1/8867_5798.PDF?UkUDh%3ACyT=)
6. [Mao, J., Xu, W., Seo, S. (2024). Exploring the dual phases of cadmium sulfide, J. Mater. Chem. A, 12, 23218](https://pubs.rsc.org/en/content/articlepdf/2024/ta/d4ta03496a)
7. [Cadmium Sulfide, CID 14783, HSDB data via PubChem](https://pubchem.ncbi.nlm.nih.gov/compound/1306-23-6)
8. [Formation of the band gap energy on CdS thin films, Thin Solid Films](https://www.sciencedirect.com/science/article/abs/pii/S0040609001008306)
9. [Cadmium yellow, CAMEO Materials Database, Museum of Fine Arts, Boston](https://cameo.mfa.org/wiki/Cadmium_yellow)
10. [Pigments through the Ages: Cadmium yellow history, WebExhibits](https://www.webexhibits.org/pigments/indiv/history/cdyellow.html)
11. [Eipper, P.-B. (2022). Degradation von Chromgelb und Cadmiumsulfid an Werken bildender Kunst, CONSERVA](https://journals.ub.uni-heidelberg.de/index.php/conserva/article/view/110979)
12. [An investigation into the synthesis of cadmium sulfide pigments, Universidade NOVA de Lisboa](https://novaresearch.unl.pt/en/publications/an-investigation-into-the-synthesis-of-cadmium-sulfide-pigments-f/)
13. [Conservation of 19th and early 20th century oil paintings, UTS Open Publications](https://opus.lib.uts.edu.au/handle/10453/37293)
14. [Unravelling complex nature of CdS/CdTe based thin film solar cells, J. Mater. Sci.: Mater. Electron.](https://link.springer.com/article/10.1007/s10854-017-7615-x)
15. [Cadmium Telluride Solar Cells, Photovoltaic Research, NLR](https://www.nlr.gov/pv/cadmium-telluride-solar-cells)
16. [Quantum dots: synthesis, bioapplications, and toxicity, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC3463453/)
17. [Synthesis, structural properties, and applications of cadmium sulfide quantum dots, Elsevier chapter (2023)](https://www.sciencedirect.com/science/article/pii/B9780323852784000180)
18. [Cadmium-Based Quantum Dots Alloyed Structures, Materials (Basel) 16, 5877 (2023)](https://pmc.ncbi.nlm.nih.gov/articles/PMC10488842/)
19. [A review on environmentally benevolent synthesis of CdS nanoparticle and their applications](https://doi.org/10.1016/j.enceco.2021.06.002)
20. [NIOSH Pocket Guide: Cadmium dust (as Cd), CDC](https://www.cdc.gov/niosh/npg/npgd0087.html)
21. [Toxicity evaluation of cadmium-containing quantum dots, PubMed review](https://pubmed.ncbi.nlm.nih.gov/33588242/)
22. [Environmentally friendly synthesis of quantum dots, Discover Nano (2025)](https://link.springer.com/article/10.1186/s11671-025-04323-6)

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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Elements and inorganic substances › Halides, nitrides, and carbides › Halides and oxohalides*

*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*

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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license