Takuya Yoshimi

TbOF complex centers in ZnS thin‐film electroluminescent devices

The effect of oxygen doping in ZnS:TbF thin‐film electroluminescent (EL) devices has been studied. We concluded that the TbOF complex center is more efficient than the TbF complex center in ZnS thin‐film EL devices. The improvement is attributed to the decreased nonradiative emission process of Tb and/or enlarged lattice distortions which generate electron‐hole pairs efficiently at the Tb excitation site.

ZnS:TbOF Thin-Film Green Electroluminescent Panels Fabricated by Two-Target Sputtering

We developed a two-target rf-magnetron sputtering system to reproducibly fabricate bright ZnS:TbOF thin-film green electroluminescent panels. ZnS and Tb are sputtered from independent targets, and the substrate moves between these targets. This results in good controllability of both ZnS thickness and Tb doping concentration. To improve luminance, we have developed a TbOF target to form efficient TbOF complex centers, and used an Ar/He mixture to avoid sputtering damage to the ZnS host. We made a prototype 640 × 200 thin-film green electroluminescent panel to demonstrate large-area capability of this system. We also made a multicolor thin-film electroluminescence panel by arranging ZnS:TbOF and ZnS:Mn active layer segments laterally.

The TbOF Complex Center and the Brightness of ZnS Thin-Film Green Electroluminescent Devices

Tb- doped ZnS thin-film is a promising material for practical green electroluminescent (EL) panels. Recently, the brightness of the green EL panels has been increased considerably [1–4]. This is mainly due to sputtering. At initial stage of development, the main advantage of sputtering is thought to be a capability of uniform doping of the emission centers of TbF3 molecules into the ZnS host [1]. Further research has revealed that the advantage of the sputtering is not only uniform doping of the emission centers but also creating efficient TbF emission centers in the ZnS host [5,6]. The EL device having TbF complex centers, which are formed during the sputtering, exhibits bright green EL. The TbF complex center consists of a substitutional Tb atom in the Zn site with a F atom in the nearest interstitial site [5]. Furthermore, we have found that oxygen doping plays an important role in obtaining high brightness [7]. In this paper, we will report our experimental results indicating that F/Tb atomic ratio is very important in obtaining high brightness, and additional doping of oxygen to the TbF complex center is very effective in further improvement. The mechanisms of these improvements are also discussed.

Brightness degradation and its mechanism in Tb‐doped ZnS thin‐film electroluminescent devices

We investigated the origin and mechanism of brightness degradation in Tb‐doped ZnS thin‐film green electroluminescent devices. We concluded that the increased number of TbF bond breaking, acting as nonradiative emission centers for Tb emission, is responsible for the degradation. The recombination energy of electron‐hole pairs generated by hot‐electron impact at the Tb‐doping site breaks the TbF bond, which is vital to efficiency. We found that high‐temperature annealing reduces the generation rate of nonradiative recombination centers, resulting in long device life.