Journal
PHYSICAL REVIEW LETTERS
Volume 122, Issue 6, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.122.067401
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Funding
- French National Agency for Research (ANR) [ANR-14-CE08-0018]
- European Union Seventh Framework Program [696656 GrapheneCore1, 785219 GrapheneCore2]
- Elemental Strategy Initiative by the MEXT, Japan
- JSPS KAKENHI [JP15K21722]
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A quantitative analysis of the excitonic luminescence efficiency in hexagonal boron nitride (h-BN) is carried out by cathodoluminescence in the ultraviolet range and compared with zinc oxide and diamond single crystals. A high quantum yield value of similar to 50% is found for h-BN at 10 K comparable to that of direct band-gap semiconductors. This bright luminescence at 215 nm remains stable up to room temperature, evidencing the strongly bound character of excitons in bulk h-BN. Ab initio calculations of the exciton dispersion confirm the indirect nature of the lowest-energy exciton whose binding energy is found equal to 300 +/- 50 meV, in agreement with the thermal stability observed in luminescence. The direct exciton is found at a higher energy but very close to the indirect one, which solves the long debated Stokes shift in bulk h-BN.
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