1 Hysteretic photochromic switching ( HPS ) in doubly 2 doped GaN ( Mg ) : Eu – a summary of recent results 3

Europium is the most-studied and least-well-understood rare earth ion (REI) dopant in 15 GaN. While attempting to increase the efficiency of red GaN light-emitting diodes (LEDs) by 16 implanting Eu+ into p-type GaN templates, the Strathclyde University group, in collaboration with 17 IST Lisbon and Unipress Warsaw, discovered hysteretic photochromic switching (HPS) in the 18 photoluminescence spectrum of doubly doped GaN(Mg):Eu. Our recent work, summarised in this 19 contribution, has used time-, temperatureand light-induced changes in the Eu intra-4f shell 20 emission spectrum to deduce the microscopic nature of the Mg-Eu defects that form in this 21 material. As well as shedding light on the Mg acceptor in GaN, we propose a possible role for these 22 emission centres in quantum information and computing. 23

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