Method for the Detailed Characterization of Cosputtered Inorganic Luminescent Material Libraries

Abstract

Understanding the behavior of combinatorially developed luminescent materials requires detailed characterization methods that have been lacking thus far. We developed a device for directly surveying the luminescent properties of thin-film libraries created through combinatorial gradient sputter deposition. Step-scan recorded excitation-, emission- and luminescence decay spectra of a thin-film library were resolved and combined with EDX measurements on the same film, relating composition to luminescent properties. This technique was applied to a single-substrate gradient thin-film library of NaBr_0.73I_0.27 to NaBr_0.09I_0.91, doped with 6.5% to 16.5% Eu²⁺. This gradient film closely followed Vegard's law, with emission fluently shifting from 428 to 439 nm. In comparison, pure NaBr:Eu²⁺ showed emission at 428 nm and NaI:Eu²⁺ at 441 nm. Luminescence decay measurements demonstrated a great degree of concentration quenching in the gradient film. From these measurements we could conclude that an optimized phosphor would most efficiently luminesce when close to NaI:Eu²⁺. This gradient film confirmed that the method presented in this work allows to both study and optimize luminescent behavior in a broad range of host- and dopant systems.