| AVS 54th International Symposium | |
| Thin Film | Friday Sessions |
| Session TF1-FrM |
| Session: | Thin Films for Displays and Flexible Electronics |
| Presenter: | M.R. Davidson, University of Florida |
| Authors: | M.R. Davidson, University of Florida S. Stoupin, Illinois Institute of Technology D.M. DeVito, Oak Ridge National Laboratory C. Segre, Illinois Institute of Technology P.H. Holloway, University of Florida |
| Correspondent: | Click to Email |
Phosphors are wide bandgap materials that contain luminescent dopants. Excitation of the dopant can result from electron-beams (cathodoluminescence), photons (photoluminescence) or even mechanical means (piezoluminescence). We have studied the local environment of the erbium (Er3+) luminescent centers in an electroluminescent (EL) ZnS:Er phosphor. The local Er environment is critical to the efficiency and, in some cases, the emission wavelength of the phosphor. Many dopants have radiative relaxation transitions that are quantum dynamically unallowed. While these transitions may be strictly unallowed in the isolated atom, in the phosphor lattice these radiative transitions typically take place with a low probability. The excited states, therefore, must be fairly long-lived in order to allow enough time for the slow radiative transition. Defects and their associated electronic states in the vicinity of the phosphor luminescent center can act to delocalize the excited states and thus provide more effective non-radiative relaxation paths. A detailed knowledge of the local chemical and structural environment is therefore necessary in order to model the quantum efficiency of the radiative relaxation. The dependence of the local composition and order in sputter deposited thin film ZnS:ErF3 electroluminescent (EL) has been investigated using EXAFS as a function of post-deposition anneal temperature. Previous results have shown that the intensity of the EL peaks in the near infrared (1.55 µm) and visible (520 nm) both increase as the anneal temperature is increased, with the NIR intensity maximizing at an anneal temperature of 425 °C . In the as-deposited films, the entire ZnS host lattice is distorted by the presence of the Er, relative to an undoped ZnS film. The long-range crystallinity improves with increasing annealing temperature, especially for 425°C < T < 475°C, the highest annealing temperature studied. The data show that the Er atoms in the as-deposited films have a maximum of one nearest neighbor S atoms, but are surrounded predominantly by F atoms (although the presence of O atoms cannot be ruled out based on EXAFS data). Upon annealing, the spacing of the S around this complex begins to collapse and at 425°C, there is a longer range order that appears.