Degradation and local distortions in electroluminescent ZnS:Cu,Cl phosphors

We present time-lapsed microscopy and EXAFS/XANES data on size selected ground ZnS:Cu,Cl and ZnS:Cu,Mn,Cl phosphors to probe long standing problems in using these phosphors in high brightness applications. The time-lapsed study shows that many of the individual emission centers on each particle degrade via large step decreases while < 50% have a monotonic decrease. These large steps suggest a break-up of Cu aggregate centers and this degradation mechanism is likely irreversible. The Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption near Edge Structure (XANES) studies show that during grinding, the CuS precipitates within the ZnS host become highly disordered yet the host material shows no disorder, suggesting that the ZnS:Cu,Cl materials cleave through the CuS precipitates during grinding.