Relationship between structural rigidity and quantum efficiency in phosphors for solid state lighting

Our article on “An integrated first principles and experimental investigation of the relationship between structural rigidity and quantum efficiency in phosphors for solid state lighting” has just been published in the Journal of Luminescence. This work is a collaborative effort between the McKittrick and Ong groups, and Jungmin Ha and Zhenbin Wang are co-first authors. In this work, we test the hypothesis of whether high host structural rigidity results in phosphors with high quantum efficiency, and show using an integrated approach that combines DFT calculations and experimental studies that a high Debye temperature alone is not a sufficient condition for a high quantum efficiency.

Upcoming talks at XXV International Materials Research Congress

Prof Ong and Zhenbin Wang will be giving the following talks at the upcoming XXV International Materials Research Congress held in Cancun, Mexico.

  1. Shyue Ping Ong, “Multi-Electron Polyanion Cathodes For High Energy Density Alkali-Ion Batteries”, Symposium B4. Materials and technologies for stationary electrochemical energy storage, Wed Aug 17 2016, 8:30am.
  2. Zhenbin Wang, “Discovery of Novel Narrow-Band Red Phosphors using High-Throughput First Principles Descriptors”, Symposium B2. Inorganic Luminescent Materials and Applications, Thurs, Aug 18 2016, 12:45 pm.

We look forward to meeting fellow scientists and researchers who are there!

Dopant segregation and embrittlement at Mo grain boundaries

Richard Tran and Zihan Xu published their paper on “Computational study of metallic dopant segregation and embrittlement at Molybdenum grain boundaries” in Acta Materialia. Mo and its alloys are important refractory materials for high temperature applications, but suffer from low ductility. In this work, we investigated the segregation and strengthening effects of 29 metallic dopants using DFT and empirical continuum models. We show that dopant chemistry and site preference plays a significant role in segregation behavior and strengthening effects at the GBs that deviate from simple bond-breaking arguments. Ta, Re, Os and W are predicted to have a weak strengthening effect on Mo for the Σ5(310) tilt GB, and Mn, Fe, Co and Nb are predicted to have reasonable strengthening effects for the Σ5(100) twist GB. Check out the paper at our publications page.

Talks at 229th ECS Meeting

Zhuoying and Iek-Heng are giving talks on their work on Na3PS4 and Li7P3S11 solid electrolytes at the 229th ECS Meeting in San Diego. Both talks are in the morning (9am and 11:30am) Wed Jun 1 in the Symposium A04 – Battery Modeling and Computation at the Hilton San Diego Bayfront – Indigo 202A.

Also, Prof Ong is one of the organizers of Symposium A04.

Electronic structure descriptor for narrow-band red phosphors

Congratulations to Zhenbin on his first paper “Electronic Structure Descriptor for Discovery of Narrow-Band Red-Emitting Phosphors” in Chemistry of Materials! Narrow-band red-emitting phosphors are a critical component in phosphor-converted light-emitting diodes for highly efficient illumination-grade lighting. In this work, we report the discovery of a quantitative descriptor for narrow-band Eu2+-activated emission identified through a comparison of the electronic structure of known narrow-band and broad-band phosphors. By incorporating this descriptor in a high throughput first principles screening of 2,259 nitride compounds, we identify five promising new nitride hosts for Eu2+-activated red-emitting phosphors that are predicted to exhibit good chemical stability, thermal quenching resistance and quantum efficiency, as well as narrow-band emission.

Insights into the Li7P3S11 superionic conductor

Iek-Heng Chu just published a new article in ACS Applied Materials & Interfaces. This is a highly collaborative work involving the expertise of many MAVRL group members as well as the Meng group. In this work, we investigate the performance limits of Li7P3S11, a highly promising lithium superionic conductor solid electrolyte. We find that Li7P3S11 is metastable at 0 K but becomes stable at above 630 K (∼360°C) when vibrational entropy contributions are accounted for, in agreement with differential scanning calorimetry measurements. Both scanning electron microscopy and the calculated Wulff shape show that Li7P3S11 tends to form relatively isotropic crystals. In terms of electrochemical stability, first-principles calculations predict that, unlike the LiCoO2 cathode, the olivine LiFePO4 and spinel LiMn2O4 cathodes are likely to form stable passivation interfaces with the Li7P3S11 SCE. This finding underscores the importance of considering multicomponent integration in developing an all-solid-state architecture. We also find that the AIMD-predicted room-temperature Li+ conductivity of 57 mS/cm is much higher than the experimental values suggesting the potential for further optimization.