Al kα

The emission scanning electron microscope (SEM) images were taken using a 20 kV MIRA4 LMH field emission SEM (TESCAN, Brno, Czech). Transmission electron microscopy (TEM) images were observed with a FEI Tecnai F30 transmission electron microscope (FEI, Hillsboro, OR, USA) operating at 100 kV. Crystal structures were determined with the aid of a SmartLab3 kW X-ray diffractometer (XRD) with Cu Kα radiation (λ = 1.5406 Å) at 40 kV and 30 mA (Rigaku, Tokyo, Japan). The Renishaw inVia Raman microscope (Renishaw, UK) and UV-3600iPLUS UV-vis-NIR spectrophotometer (Shimadzu Scientific Instruments, Kyoto, Japan) were used to acquire the Raman spectra and the extinction spectra, respectively. Nicolet iS50 (Thermo Fisher Scientific, Waltham, MA, USA) FTIR spectra were obtained for this study. XPS test was performed on Thermo Scientific K-Alpha using an Al Kα excitation source at 6 mA and 12 kV (Thermo Fisher Scientific, USA). A TCP-5100-VDV inductively coupled plasma–mass spectrometer (ICP-MS) was used to analyze the composition quantitatively (NYSE: A, Malaysia). Malvern Zetasizer Nano ZSE analyzer was used to determine the hydrodynamic size and zeta potential (Malvern, UK).

Powder X-ray diffraction (PXRD) data was collected on a Stoe StadiP diffractometer using Cu Kα1 (λ = 1.54056 Å) radiation. 0.5 mm capillaries were filled with powdered samples and data were collected over the 2θ range 5–60° in steps of 0.5° at 20 s per step. Optical diffuse-reflectance data was recorded between 300 and 2000 nm, with a data collection step of 1 nm, using a Lambda 950 spectrophotometer equipped with an integrating sphere at ambient temperature. AgCuS and the Ag₃CuS₂ were pressed into 13 mm diameter pellets at 5 bar with thicknesses of 1.04 mm and 1.24 mm for AgCuS and Ag₃CuS₂ respectively. The Hall coefficient, electrical resistivity, carrier concentration and carrier mobility of the AgCuS pellet were measured using van der Pauw geometry on a Ecopia Hall Measurement System (HMS-3000) at room temperature using four silver paint contacts. Four point probe measurements were performed, giving sheet resistance for Ag₃CuS₂, as resistance was too high for Hall effect measurement. X-ray photoemission spectroscopy (XPS) measurements were recorded using a Thermo Scientific Al-Kα.

UV/Vis absorption and fluorescence spectra measurements were performed on a multimode reader Spark® 10M (Tecan, Männedorf, Switzerland). Scanning electron microscopy (SEM) images were obtained on a field-emission scanning electron microscope with X-MaxN energy spectrum (ZEISS, Jena, Germany). X-ray photoelectron spectroscopy (XPS) data were recorded using K-Alpha using Al Kα (hv = 1486.6 eV) radiation (Thermo Scientific, Waltham, USA). X-ray diffraction (XRD) patterns were recorded from a D8 ADVANCE (Bruker, Karlsruhe, Germany) X-ray diffracto meter with Cu Kα radiation (λ = 1.5406 Å). Fourier transform infrared spectra were obtained using a Bruker ALPHA spectrophotometer (Bruker, Karlsruhe, Germany). The zeta potential was measured with a Zetasizer Nano ZS DLS system (Malvern Instruments Ltd., Malvern, England). N₂ adsorption/desorption isotherms were obtained using an ASAP 2020 HD88/Autosorb IQ system (Quantachrome, Florida, USA) at 77 K. Fluorescence microscope images were recorded by NIS-Elements Viewer (Nikon, Tokyo, Japan). Mass spectrum data were collected from QE (Thermo Scientific, Waltham, USA).