Nonlinear Optical-Active NaAlP₂S₆ Synthesized by the MOBQ Method: Synthesis, Structure, and Optical Properties

Area of Science:

• Materials Science
• Solid-State Chemistry
• Optoelectronics

Background:

• Group 13 metal chalcogenides are vital infrared nonlinear optical (NLO) crystals.
• Group 13 metal chalcophosphates, especially Al-based, are underexplored.
• Al-based functional motifs hold potential for advanced NLO applications.

Purpose of the Study:

• To synthesize and characterize a novel quaternary thiophosphate, NaAlP2S6.
• To investigate the structural and NLO properties of NaAlP2S6.
• To explore the potential of Al-based chalcophosphates for NLO applications.

Main Methods:

• Synthesis via reactive flux NaCl-assisted metal oxide-boron-chalcogen (MOBQ) solid-state method.
• Crystallographic analysis to determine the orthorhombic Fdd2 structure.
• Experimental and theoretical calculations to evaluate optical properties and NLO response.

Main Results:

• NaAlP2S6 crystallizes in a 3D framework of AlS6 octahedra and P2S6 dimers.
• The material exhibits a wide bandgap (3.72 eV) and a moderate second harmonic generation (SHG) response (0.25 × AgGaS2).
• NaAlP2S6 demonstrates an ultrahigh laser-induced damage threshold (LIDT) of 14.7 × AgGaS2.

Conclusions:

• NaAlP2S6 is a promising new material for NLO applications.
• The P2S6 dimers are the primary contributors to the SHG response.
• Al-based chalcophosphates represent a new avenue for designing high-performance NLO crystals.