Comparative crystal analysis

High‑quality nonlinear optical and laser crystals for IR and THz bands

Chalcogenides: Properties and Applications

Chalcogenides are binary compounds of chalcogens (elements of Group 16 of the periodic table — sulfur, selenium, tellurium, polonium, livermorium) with metals. They are widely used in optics, electronics, laser technology, solar energy and other fields due to their semiconductor, luminescent, nonlinear‑optical and other properties [1][20][8].

Among the most well‑known chalcogenide crystals are sulfides, selenides and tellurides of various metals, as well as chalcogenide glasses. Let’s look at some of them and conduct a comparative analysis.

Sulfides

Examples: ZnS (zinc sulfide), CdS (cadmium sulfide), Cu2ZnSnS4 (kesterite).

Properties:

commonly used in semiconductor devices and photovoltaic cells;
have a relatively narrow band gap, which makes them suitable for absorbing sunlight;
some sulfides (e.g., ZnS) are used in optics as materials with high transparency in the UV range.

Applications: solar cells, light‑emitting diodes (LEDs), laser materials.

Selenides

Examples: ZnSe (zinc selenide), GaSe (gallium selenide), CdSe (cadmium selenide).

Properties:

have a wider band gap compared to sulfides;
ZnSe is transparent in the range from 0,62 to 19 μm, but has a low optical damage threshold (2–3 kW/cm2);
GaSe is a non‑centrosymmetric crystal with a wide transparency range (0,62–20 μm), used in nonlinear optics for THz radiation generation;
exhibits high birefringence (~0,35 at a wavelength of 1 μm), which allows satisfying phase‑matching conditions [4].

Applications: infrared optics, nonlinear optical devices, ionizing radiation detectors.

Tellurides

Examples: CdTe (cadmium telluride), HgTe (mercury telluride), GeTe (germanium telluride).

Properties:

CdTe is one of the leaders in solar energy due to its high energy conversion efficiency (over 20 %);
HgTe is used in thermoelectric devices and as a material with temperature‑dependent conductivity;
GeTe is part of phase‑change materials (e.g., GeSbTe), used in non‑volatile memory.

Applications: solar cells, IR radiation detectors, phase‑change memory.

Chalcogenide Glasses

Examples: As2S3, GeS2, GeAsSe.

Properties:

amorphous materials formed from sulfides, selenides and tellurides;
opaque to visible light but transparent in the IR range;
low‑melting, requiring rapid cooling to prevent crystallization;
exhibit semiconductor‑type electronic conductivity and internal photoelectric effect [9];
low phonon energy (300–450 cm−1) allows observing radiative transitions in the mid‑IR range [21].

Applications: rewritable optical discs (CD‑RW, DVD‑RW), phase‑change memory devices (PRAM), infrared optics, lasers.

Parameter	Sulfides	Selenides	Tellurides	Chalcogenide Glasses
Band gap	Narrow	Wide	Medium	Depends on composition
Transparency	UV range (e.g., ZnS)	IR range (e.g., ZnSe)	IR range	IR range
Applications	Solar energy, LEDs	Nonlinear optics, IR detectors	Solar energy, memory	Optical discs, memory, IR optics
Key features	Commonly used in photovoltaics	High birefringence (GaSe)	Phase change (GeTe)	Amorphous structure, low‑melting

Conclusions

Chalcogenide crystals differ in composition, properties and applications. Sulfides are more often used in solar energy and LEDs, selenides — in nonlinear optics and IR detectors, tellurides — in solar energy and phase‑change memory. Chalcogenide glasses are applied in rewritable optical media and IR optics. The choice of a specific material depends on the required properties: band gap width, transparency, electrical conductivity and other parameters.