and internal charge, respectively. For full-stack device, annealing causes increases of

31% and 40% in external conduction and internal charge, respectively. Annealing has

been reported to increase the film crystallinity [50] and the infrared intensity. Based on

this study, increased crystallinity allows an increased conduction charge and

consequently an improved brightness.

 Fig 4.8 shows that capacitance above turn-on is about 1-2 times larger for half-

stack device than that for full-stack device. The explanation for this is that as the voltage

goes above turn on, the phosphor breaks down so that the device becomes one capacitor

for half-stack and two capacitors in series for full-stack. It can be seen that the

capacitance for one capacitor is larger than that for two capacitors in series, which is the

main reason for increased conduction charge in half-stack devices.

 ZnS:TmF3 devices were also studied in this research. However, data were collected

only from as-deposited films. The data in Fig 4.9 to 4.10 show the same trends as are

observed for ZnS:ErF3 devices. Half-stack device exhibits a 40V lower turn-on voltage, a

three times higher near-infrared intensity, and a 100% higher near-infrared/visible ratio.

For half-stack devices, the external conduction and internal charges are 80% and 60%

larger than for full-stack devices, respectively. Fig 4.13 shows that capacitance above

turn-on is 100% larger for half-stack device than that for full-stack device, which again

would result in increased conduction charge.