Diffuse Reflectance measurements were performed on an Agilent Technologies Cary 60 UV-Vis spectrometer with a Harrick Scientific VideoBarrelino Diffuse Reflectance attachment, using BaSO4 as a 100% reflectance background standard. For the plotting of the indirect gap, the background at low energies (between 1.1 and 1.15 eV) was subtracted for better comparison and for extraction of the band gap energy Secondary Electron Microscopy (SEM) and Energy Dispersive X-Ray spectroscopy (EDX) was performed using a Carl Zeiss Gemini SEM 300 with a field emission. EDX was analysed using an Oxford Instruments Aztec Energy EDS analysis system with an XMax 80 detector. The Oxford Instruments Aztec Energy software suite was used for analysis. Samples were coated with 15nm of carbon prior to measurement to prevent charging. Samples were imaged and analysed using an accelerating voltage of 15 kV. Density functional theory (DFT) calculations of the energy and electronic structure of SrxBi4-xO4Se1-xCl2+x and CaBi3O4Cl3 compounds were performed using the projector augmented wave (PAW) approach in the VASP code . Non-spin polarised calculations were performed using the Perdew-Burke-Ernzerhof (PBE) functional . Geometry optimisations were performed using a plane-wave cut-off of 520 eV and a gamma centred k-point mesh with a density of ≥28 Å.