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ABSTRACT Current shortage of UV light‐emitting diodes ( ) with high external quantum efficiency for commercial use motivates the search for alternative cost‐effective methods of generating UV light. One approach is blue‐to‐UV upconversion with Pr 3+ that would rely on phosphor‐converted LED technology. We recently identified Cs 2 NaYCl 6 :Pr 3+ as an interesting compound for effective ESA‐based blue‐to‐UV upconversion with this ion. Co‐activation with Gd 3+ does result in narrow‐line emission at around interesting for germicidal lamps and indicates an effective energy transfer. It was our motivation to understand the mechanism of this energy transfer from Pr 3+ to Gd 3+ in microcrystalline Cs 2 NaYCl 6 for better design. For that purpose, we used steady‐state and time‐resolved spectroscopy at to resolve the intrinsic excited‐state dynamics while limiting other disturbing nonradiative relaxation processes. Decay analysis using the shell model shows increasing 3 P 0 decay rates with higher Pr 3+ content due to cross‐relaxation and clearly indicates additional Na site occupation also confirmed by Rietveld analysis of the powder X‐ray diffraction patterns. Overall, an energy transfer to Gd 3+ occurs with a surprisingly high efficiency of and demonstrates that energy transfer can also resolve local structural phenomena relevant for the design of next‐generation blue‐to‐UV upconversion phosphors with Pr 3+ .
Förster et al. (Mon,) studied this question.