Li2HgMS4 (M = Si, Ge, Sn) - New Quaternary Diamond-Like Semiconductors for Infrared Laser Frequency Conversion

At a Glance

Metadata	Details
Publication Date	2017-04-12
Journal	Crystals
Authors	Kui Wu, Shilie Pan
Institutions	Xinjiang Technical Institute of Physics & Chemistry
Citations	56
Analysis	Full AI Review Included

Technical Analysis of $\text{Li}{2}\text{HgMS}{4}$ DLS Compounds for Frequency Conversion

Executive Summary

The research details the successful synthesis and characterization of a new family of quaternary Diamond-Like Semiconductors (DLSs), $\text{Li}{2}\text{HgMS}{4}$ (M = Si, Ge, Sn), identified as highly promising candidates for mid-infrared (IR) Nonlinear Optical (NLO) applications. The key findings and value proposition for high-power optical engineering include:

Exceptional Laser Damage Threshold (LDT): $\text{Li}{2}\text{HgSiS}{4}$ and $\text{Li}{2}\text{HgGeS}{4}$ exhibit LDTs approximately 3.0 times and 2.3 times, respectively, greater than the commercial benchmark $\text{AgGaS}_{2}$.
Wide IR Transparency: All compounds show wide IR transmission regions (2.5-23.5 µm), covering critical atmospheric windows (3-5 µm and 8-12 µm) essential for telecommunications and laser guidance.
Strong SHG Response: The compounds demonstrate significant Second Harmonic Generation (SHG) coefficients, with $\text{Li}{2}\text{HgSnS}{4}$ achieving 4.0 times the SHG intensity of $\text{AgGaS}_{2}$ at key particle sizes.
High Optical Bandgap (E_g): Calculated bandgaps (2.32-2.68 eV) are significantly larger than existing commercial IR NLO materials (e.g., $\text{AgGaSe}_{2}$ at 1.80 eV), contributing directly to enhanced LDT.
Non-Centrosymmetric Structure: The isostructural compounds crystallize in the polar space group $Pmn2_1$, a non-centrosymmetric (NCS) structure necessary for effective SHG function.
Synthesis Method: Crystals were synthesized using a high-temperature solid-state method (700 °C) in vacuum-sealed silica tubes, indicating stability under elevated processing conditions.

Technical Specifications

Parameter	Value	Unit	Context
Crystal System	Orthorhombic	N/A	$\text{Li}{2}\text{HgMS}{4}$ compounds
Space Group	$Pmn2_1$	N/A	Polar, non-centrosymmetric (NCS)
Optical Bandgap (E_g)	2.68	eV	$\text{Li}{2}\text{HgSiS}{4}$
Optical Bandgap (E_g)	2.46	eV	$\text{Li}{2}\text{HgGeS}{4}$
Optical Bandgap (E_g)	2.32	eV	$\text{Li}{2}\text{HgSnS}{4}$
LDT	91.6	MW/cm²	$\text{Li}{2}\text{HgSiS}{4}$ (Pulsed YAG laser, 1.06 µm)
LDT (Relative)	~3.0	x $\text{AgGaS}_{2}$	$\text{Li}{2}\text{HgSiS}{4}$
LDT	70.2	MW/cm²	$\text{Li}{2}\text{HgGeS}{4}$
LDT (Relative)	~2.3	x $\text{AgGaS}_{2}$	$\text{Li}{2}\text{HgGeS}{4}$
SHG Response (Relative)	4.0	x $\text{AgGaS}_{2}$	$\text{Li}{2}\text{HgSnS}{4}$ (55-88 µm particle size)
IR Transmission Window	2.5-23.5	µm	$\text{Li}{2}\text{HgSnS}{4}$ (Widest range)
LDT Excitation Wavelength	1.06	µm	Pulsed YAG Laser
SHG Excitation Wavelength	2.09	µm	Q-switch Laser
LDT Pulse Duration/Freq.	10 ns, 10 Hz	N/A	High-power regime

Key Methodologies

The synthesis and characterization of the $\text{Li}{2}\text{HgMS}{4}$ DLS materials utilized specialized high-temperature processing and rigorous optical testing required for NLO candidates:

Solid-State Synthesis: Target materials were prepared via high-temperature solid-state reaction of starting materials (Li:HgS:(Si/Ge/Sn):S) sealed under vacuum in silica tubes.
Crucible Management: A graphite crucible was included in the sealed silica tube to prevent reactions between the elemental Lithium (Li) and the silica tube at high temperatures ($\geq$ 700 °C).
Specific Thermal Recipe:
- Heating: Slowly heated to 700 °C over two days.
- Soak: Kept at 700 °C for approximately four days.
- Cooling: Slowly cooled down to 300 °C over four days, followed by quick cooling to room temperature.
Purification: Obtained crystals were repeatedly washed using N,N-dimethylformamide (DMF) solvent to eliminate byproducts.
Optical Property Characterization:
- Bandgap Determination: UV-Vis-NIR Diffuse-Reflectance Spectroscopy (190-2600 nm) converted via the Kubelka-Munk function.
- Second Harmonic Generation (SHG): Kurtz and Perry method using a Q-switch laser (2.09 µm) on ground micro-crystals of specific particle sizes (55-88 µm).
- Laser Damage Threshold (LDT): Measured on ground micro-crystals (55-88 µm) using a high-power pulsed YAG laser (1.06 µm, 10 ns, 10 Hz), using $\text{AgGaS}_{2}$ powder as the reference.

6CCVD Solutions & Capabilities

The development of high-performance IR NLO crystals, such as the $\text{Li}{2}\text{HgMS}{4}$ family, demands substrates and optical components that can survive the extreme power densities generated by frequency conversion (LDT up to 91.6 MW/cm²). MPCVD Diamond from 6CCVD is the ideal enabling material for this next generation of high-power IR optics and component integration.

Applicable Materials

To replicate, test, or integrate these high-LDT NLO crystals, CVD Diamond provides the required thermal management and intrinsic laser resistance.

Material Requirement	6CCVD Solution	Rationale for Application
High-Power Window/Output Coupler	Optical Grade SCD (Single Crystal Diamond)	Intrinsic bandgap of 5.5 eV, zero grain boundaries, and the highest thermal conductivity available (up to 2200 W/mK). Crucial for components handling multi-MW/cm² power without thermal lensing or failure.
Large-Area Substrates for Thin-Film NLO Growth	High-Purity PCD (Polycrystalline Diamond)	Available in diameters up to 125mm, suitable for scaling up thin-film or heteroepitaxial growth of DLS materials. Highly stable platform required for high-temperature synthesis (e.g., 700 °C).
IR Laser Control Components	SCD or PCD, up to 500µm thickness	Diamond is transparent across the entire 2.5-23.5 µm IR range highlighted in the research, making it ideal for packaging or isolating the NLO element.

Customization Potential

The advancement of these NLO materials from powdered samples (55-88 µm) to manufacturable bulk crystals or thin-film integrated devices requires precision engineering, which 6CCVD provides:

Precision Substrates: If the research transitions to thin-film DLS structures, 6CCVD offers diamond wafers up to 125mm with superior polishing (Ra < 1nm for SCD, Ra < 5nm for inch-size PCD), ensuring the surface quality necessary for high-quality epitaxy and minimizing scattering losses in the IR.
Custom Dimensions and Shaping: We provide precise laser cutting and shaping services to create specific optical elements, such as wedge prisms or protective windows, matching the dimensions of custom NLO cells.
Metalization Services: While the NLO crystal itself does not require metalization, integration into a high-power system demands robust electrical contacts or bonding layers. 6CCVD offers in-house metalization capabilities including Ti/Pt/Au, W/Cu, and Pd, essential for mounting, cooling, or sensor integration in IR systems.

Engineering Support

6CCVD’s in-house PhD team can assist researchers and engineers with material selection and design optimization for projects focused on High LDT Infrared Frequency Conversion. Whether the goal is maximizing thermal dissipation, minimizing two-photon absorption (TPA), or achieving optimal surface flatness for integrated optics, we provide expert consultation tailored to the unique demands of DLS crystal systems.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available) to support advanced research worldwide.

View Original Abstract

A new family of quaternary diamond-like semiconductors (DLSs), Li2HgMS4 (M = Si, Ge, Sn), were successfully discovered for the first time. All of them are isostructural and crystallize in the polar space group (Pmn21). Seen from their structures, they exhibit a three-dimensional (3D) framework structure that is composed of countless 2D honeycomb layers stacked along the c axis. An interesting feature, specifically, that the LiS4 tetrahedra connect with each other to build a 2D layer in the ac plane, is also observed. Experimental investigations show that their nonlinear optical responses are about 0.8 for Li2HgSiS4, 3.0 for Li2HgGeS4, and 4.0 for Li2HgSnS4 times that of benchmark AgGaS2 at the 55-88 μm particle size, respectively. In addition, Li2HgSiS4 and Li2HgGeS4 also have great laser-damage thresholds that are about 3.0 and 2.3 times that of powdered AgGaS2, respectively. The above results indicate that title compounds can be expected as promising IR NLO candidates.

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst7040107

References

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