Blue- and green-emitting SrS:Cu electroluminescent devices deposited by the atomic layer deposition technique

Abstract

Observed structural, compositional, and optical differences between blue- and green-emitting SrS:Cu thin films deposited by the atomic layer deposition technique were studied. The use of hydrogen in the deposition process resulted in green-emitting electroluminescent devices. The green-emitting devices had also the highest potassium (K) content, but the exact role of K was not resolved. The green emission is thought to originate from copper pairs and isolated off-centered copper ions at octahedral sites, whereas blue emission is suggested to originate from copper ions at tetrahedral interstitial sites. The brightest blue-emitting device, measured at 60 Hz, emitted 17 cd/m2 at 40 V above the threshold voltage (L40) with x=0.17 and y=0.30 as the Commission Internationale de l’Eclairage color coordinates. Conversely, the brightest green-emitting device emitted 44 cd/m2 with x=0.33 and y=0.58. The blue- and green-emitting devices also showed different time-resolved electroluminescence behavior, which suggests reduced dynamic space charge within the green-emitting phosphors resulting in the higher emission intensity in the green-emitting devices.