Two-dimensional layered gallium monochalcogenide (GaX, where X = S, Se, Te) semiconductors possess great potential for use in optoelectronic and photonic applications, owing to their direct band edge. In this work, the structural and optical properties of full-series multilayer GaTe1−xSex for x = 0 to x = 1 are examined. The experimental results show that the whole series of GaTe1−xSex layers may contain one hexagonal (H) phase from GaTe to GaSe, whereas the monoclinic (M) phase predominates at 0 ≤ x ≤ 0.4. For x ≥ 0.5, the H-phase dominates the GaTe1−xSex series. The micro-photoluminescence (μPL) results indicate that the photon emission energy of M-phase GaTe1−xSex increases as the Se content increases from 1.652 eV (M-GaTe) to 1.779 eV (M-GaTe0.6Se0.4), whereas that of H-phase GaTe1−xSex decreases from 1.998 eV (H-GaSe) to 1.588 eV (H-GaTe) in the red to near-infrared (NIR) region. Micro-time-resolved photoluminescence (TRPL) and area-fluorescence lifetime mapping (AFLM) of the few-layer GaTe1−xSex series indicates that the decay lifetime of the band-edge emission of the M phase is faster than that of the H phase in the mixed alloys of layered GaTe1−xSex (0 ≤ x ≤ 0.4). On the other hand, for H-phase GaTe1−xSex, the decay lifetime of the band-edge emission also increases as the Se content increases, owing to the surface effect. The dark resistivity of GaTe1−xSex for 0.5 ≤ x ≤ 1 (i.e., predominantly H phase) is greater than that of the other instance of majority M-phase GaTe1−xSex for 0 ≤ x ≤ 0.4, owing to the larger bandgaps. The predominantly H phase GaTe1−xSex (0.5 ≤ x ≤ 1) also shows a greater photoconductive response under visible-light illumination because of the greater contribution from surface states. The superior light-emission and photodetection capability of the GaTe1−xSex multilayers (0 ≤ x ≤ 1) means that they can be used for future optoelectronic devices.

Near‐band‐edge emissions ranging from red (≈630 to 602 nm) to green (≈550 to 534 nm) and blue (≈494 to 480 nm) colors have been detected in full‐series GaSe1‐xSx (0≤x≤1) multilayers using micro‐photoluminescence (µPL) measurements from 4 to 300 K. The multilayered chalcogenides crystallize in a hexagonal structure, with observed mixed stacking phases of ε and β polymorphs through X‐ray diffraction and Raman measurements. The µPL results, along with experimental band‐edge characterization through thermoreflectance, identify the ε‐stacked phase as the crucial phase responsible for direct recombination and the emission of free excitons within the visible range. A mixed‐color white light is created by PL, which is emitted from the layered GaSe1‐xSx series of different colors, and is positioned at the center of the CIE coordination plot (i.e., white color). To assess the emission properties of both band edges and defects in the layered compounds, time‐resolved photoluminescence (TRPL) is employed, using an area mapping function. The photoluminescence decay lifetime increases as the sulfur content is increased, owing to the greater occurrence of mixed‐phase stacking faults near the β‐GaS end within the GaSe1‐xSx (0≤x≤1) series. The multilayer GaSe1‐xSx (0≤x≤1) represents a distinct 2D chalcogenide series well‐suited for emitting full‐color visible light.