In recent years, metal–halide perovskites (MHPs) have emerged as highly promising optoelectronic materials based on their exceptional properties and versatility in applications such as solar cells, light-emitting devices, and radiation detectors. This study investigates the optical properties of two-dimensional (2D) MHPs, with the Ruddlesden–Popper structure, comparing three morphologies–bulk poly-crystals, colloidal nanoplatelets (NPs), and thin films, aiming to bridge between the bulk and nano dimensionalities. By synthesizing bulk 2D MHPs using long alkyl ammonium spacers, typically found in colloidal systems, and NPs using shorter ligands suitable for bulk growth, we elucidate the relationship between these materials’ structural modifications and optical characteristics. We propose the existence of two regions in these 2D MHPs, which differ in their optoelectronic properties and are associated with “bulk” and “surface” regions. Specifically, for poly-crystals, we observe the appearance of a lower energy “bulk” phase associated with the stacking of many 2D sheets, apparent both in absorption and photoluminescence. For NPs, this stacking is hindered, and hence, only the “surface” phase exists. With the elongation of the spacer chain, the poly-crystal becomes more similar to the NPs. For thin films, an interesting phenomenon is observed – the rapid film formation mechanism forces a more colloid-like structure for the shorter ligands and a more poly-crystal-like structure for the longer ones. Overall, this study bridging the different dimensions of 2D MHPs may support new possibilities for future research and development in this innovative field.

Low-dimensional halide perovskites (LDHPs) are promising candidates for optoelectronic applications, specifically light emission. LDHP’s reduced-dimensional frameworks allow exceptional tunability of the optoelectronic properties. Self-trapped exciton emission (STE) is an intriguing characteristic of some LDHPs, offering a compelling mechanism for white-light emission. In this work, we study the effect of halide substitution and synthetic methods on the optical properties, with a particular focus on STE emission, of one-dimensional LDHPs using (2,5-dmpz)Pb(BrxCl1–x)4 (dmpz = dimethylammonium piperazine) as a model system, exhibiting high emission quantum efficiency and structural consistency. Mechanochemical approaches, including manual grinding and ball milling, were employed to synthesize pure and mixed halide compounds, enabling precise composition control. Structural characterization revealed that ball milling produces materials with improved crystallinity and a homogeneous halide distribution. Optical characterization showed an anticorrelation between the absorption onset and STE emission energies, with STE properties influenced by both halide composition and a synthesis route. Moreover, we found that the STE emission of the mixed halide compounds evolved with time. The post-synthesis evolution of the STE emission spectrum is associated with local lattice distortions rather than long-range structural changes. The emission quantum efficiency of these compounds was measured and reached a value of 35%, among the highest values measured for 1D broad emitters. These findings provide additional insights into the design of next-generation LDHP compounds exhibiting STE emission and development of white-light-emitting devices based on them.

Syngas, a vital H2 and CO mixture, is crucial for industrial applications and advancing the circular carbon economy. Traditional photocatalytic CO2 reduction to syngas relies on sacrificial agents and photosensitizers, limiting scalability and practice. Here, we demonstrate a Co3O4–CdS heterojunction photocatalyst that efficiently converts formate (HCOO−), a stable, easily-handled and accessible CO2 reduction product, into syngas under alkaline conditions (pH ∼ 10). This dual-function catalyst enables CO generation via CdS-mediated dehydration and H2 production via Co3O4-mediated dehydrogenation, achieving a syngas production rate of ∼3300 μmol g−1 h−1. Notably, this system operates without sacrificial agents or noble metals, with near-zero CO2 emissions, surpassing current efficiency benchmarks. By recycling CO2 into formic acid and further converting it to syngas, this approach promotes a closed carbon loop. Its cost-effectiveness, ease of formate storage, direct solar utilization, and low carbon footprint position it as a promising pathway for sustainable syngas production and clean energy solutions.