Maize (Zea mays L.) germplasm in China Summer maize ecological region (CSM) or central corn-belt of China is diverse but has not been systematically characterized at molecular level. In this study, genetic variation, genome diversity, linkage disequilibrium patterns, population structure, and characteristics of different heterotic groups were studied using 525,141 SNPs obtained by Genotyping-By-Sequencing (GBS) for 490 inbred lines collected from researchers at CSM region. The SNP density is lower near centromere, but higher near telomere region of maize chromosome, the degree of linkage disequilibrium (r2) vary at different chromosome regions. Majority of the inbred lines (66.05%) show pairwise relative kinship near zero, indicating a large genetic diversity in the CSM breeding germplasm. Using 4849 tagSNPs derived from 3618 haplotype blocks, the 490 inbred lines were delineated into 3 supergroups, 6 groups, and 10 subgroups using ADMIXTURE software. A procedure of assigning inbred lines into heterotic groups using genomic data and tag-SNPs was developed and validated. Genome differentiation among different subgroups measured by Fst, and the genetic diversity within each subgroup measured by GD are both large. The share of heterotic groups that have significant North American germplasm contribution: P, SS, IDT, and X, accounts about 54% of the CSM breeding germplasm collection and has increased significantly in the last two decades. Two predominant types of heterotic pattern in CSM region are: M-Reid group × TSPT group, and X subgroup × Local subgroups.

Green light causes the maximum luminous sensation in human eyes, which has many advantages for potential uses. However, the efficiency of light-emitting diodes (LEDs) in the green wavelength range (495−570 nm) is much lower than that in the red or blue region, which is known as the "green gap" problem. In this study, we report the strong green photoluminescence in metastable Zr 3 N 4 thin films with an orthorhombic structure for the first time. Crystallized Zr 3 N 4 thin films have been successfully grown by high-power impulse magnetron sputtering. Notable green photoluminescence in the wavelength region of 490−535 nm has been identified in such orthorhombic Zr 3 N 4 thin films even at room temperature. In addition, a joint experimental and theoretical study has been performed to investigate its electronic structures and to reveal the origins of such green light emissions. The calculations of the transition dipole moments demonstrate that the direct transition between the conduction band minimum and the energy level II below the valence band maximum is responsible for such strong green photoluminescence. This work may pave a new way to solve the "green gap" problem in LEDs with low cost.