  Historically, the discovery and optimization of doped bulk materials has been
predominantly developed through an Edisonian approach. While successful and
despite the constant progress in fundamental understanding of detector
materials physics, the process has been restricted by its inherent slow pace
and low success rate. This poor throughput owes largely to the considerable
compositional space that needs to be accounted for to fully comprehend complex
material/performance relationship. Here, we present a combinatorial approach
where doped bulk scintillator materials can be rapidly optimized for their
properties through concurrent extrinsic doping/co-doping strategies. The
concept that makes use of Design of Experiment, rapid growth and evaluation
techniques, and multivariable regression analysis, has been successfully
applied to the engineering of NaI performance, a historical but mediocre
performer in scintillation detection. Using this approach, we identified a
three-element doping/co-doping strategy that significantly improves the
material performance. The composition was uncovered by simultaneously screening
for a beneficial co-dopant ion among the alkaline earth metal family and by
optimizing its concentration and that of Tl+ and Eu2+ ions. The composition
with the best performance was identified as 0.1% mol Tl+, 0.1% mol Eu2+ and
0.2% mol Ca2+. This formulation shows enhancement of energy resolution and
light output at 662 keV, from 6.3 to 4.9%, and from 44,000 to 52,000 ph/MeV,
respectively. The method, in addition to improving NaI performance, provides a
versatile framework for rapidly unveiling complex and concealed correlations
between material composition and performance, and should be broadly applicable
to optimization of other material properties.
