Author contributions The idea for this project was conceived by M.G.K., D.Y.C., D.G.C. and Y.H.
The manuscript was written by D.G.C., Y.H. and M.G.K. with input from all authors. D.G.C.
developed the synthetic and crystal growth methods. The crystal structure and physical
properties, excluding the optical properties, were measured by D.G.C. The band structure and
effective-mass calculations were conducted by G.T. Optical transmission measurements were
performed by K.M.M. and Z.L. K.M.M. measured the variable-temperature and power-
dependent PL and the Raman spectra. Y.H. and D.G.C. fabricated the devices and performed
pulse-height spectrometry of the^241 Am and^57 Co sources. Neutron measurements were
performed by R.O.P., Y.H., D.G.C., D.Y.C. and P.M.D.L. M.G.K. and B.W.W. supervised the project.
Competing interests The authors declare the U.S. patent application 62/701,144.Additional information
Correspondence and requests for materials should be addressed to M.G.K.
Peer review information Nature thanks Paul Sellin and Mariya Zhuravleva for their contribution
to the peer review of this work.
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