1：Experimental Design and Method Selection:

Optical analysis was performed by absorption and photoluminescence spectroscopy. High resolution X-ray diffraction measurements were carried out to investigate the structural quality of the grown crystal. Secondary ion mass spectrometry (SIMS) was performed to detect transition metal contamination.

2：Sample Selection and Data Sources:

Unintentionally doped GaN grown by hydride vapor phase epitaxy that exhibits a sharply delimited region of green color was investigated.

3：List of Experimental Equipment and Materials:

Specord 600 UV-VIS spectrometer, HeCd laser, NKT SuperK Extreme supercontinuum laser, 0.5 m monochromator equipped with a liquid nitrogen cooled CCD camera, μ-PL setup with a laser spot focused to a diameter of 1 μm, 0.8 m monochromator equipped with a thermoelectrically cooled CCD camera.

4：5 m monochromator equipped with a liquid nitrogen cooled CCD camera, μ-PL setup with a laser spot focused to a diameter of 1 μm, 8 m monochromator equipped with a thermoelectrically cooled CCD camera. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Absorption spectroscopy measurements at room temperature and 80 K were performed. PL excited by a 325 nm HeCd laser was performed at 15 K and room temperature. PLE was excited by a NKT SuperK Extreme supercontinuum laser with a tunable bandpass filter. Room temperature PL line scans along the optical axis of an m-plane cross section were performed.

5：Data Analysis Methods:

PL and PLE spectra were corrected for spectral response of the system. The spectral resolution of the PL setup is about 0.5 meV in the NIR spectral range.