Phosphor Technology Center of Excellence
The PTCOE phosphor characterization facility currently has two high vacuum systems available for cathodoluminescence (CL) characterization of phosphor powders, screens, and thin films. A third system is also being developed to test phosphor screens using field emission cathodes. The facility employs two 0-5 kV electron guns, and one 1-30 kV gun. These guns enable the CLc research and development. The e-guns are typically operated in continuous mode for intrinsic efficiency measurements, but most can also be pulsed to simulate the operational conditions in a display environment and investigate saturation effects. One of the e-guns can generate pulse widths down to 10 ns, which is important when evaluating the dynamics of the new fast phosphors. The pulsing capability is supported by a number of pulse generators, with peak voltages of up to 300 V. Each e-gun has different current density characteristics, ranging from 25 to about 100 mA/cm2 at the highest operating voltages. The target current densities are determined by using a Faraday cup to measure the current, and a stereomicroscope with a CCD camera to measure the target spot size. Imaging software is also used to evaluate the intensity profile of the electron beam. In addition to the electron gun capabilities, 2 inch diagonal field emission cathodes have also been used as an electron source. These cathodes can be tested inside the existing vacuum systems, but a dedicated system is currently being developed to allow greater flexibility. The use of cold cathodes provides an opportunity to test phosphor screens in a realistic FED environment. A special test fixture for the cathodes allows evaluation of multiple phosphor screens at one time. The current electronics enables cathode testing to be performed at FED duty cycles up to 10 kV. Video equipment is also available for the documentation and presentation of the FED performance.
Several optical instruments are available for photometric, spectral, and time-dependent measurements. We currently have a Graseby 370 and a Photo Research PR880 photometer, which are used for brightness measurements. A 4 inch Labsphere integrating sphere also enables the measurement of absolute luminous flux. The CL emission spectra and chromaticity are measured by an Oriel 125 mm spectrometer. The time-dependence of the emission at a given wavelength is observed by a CVI 125 mm monochromator and PMT combination, with a time response of about 10 ns. A determination of the CL time-dependence is extremely useful in elucidating the affects of saturation and thermal quenching on the phosphor dynamics. All of the support electronics used in the CL characterization are presently being integrated under computer control. A computer is dedicated to each vacuum system, and performs the necessary data acquisition functions required for that system using LabVIEW software. These computers will all be interconnected, enabling the quick transfer of information between computers. A central phosphor database is also under development. Therefore, once the data has been acquired and processed, it will be downloaded to the phosphor database and made available through the internet to all the PTCOE members.
For more information, please contact:
Dr. Chris Summers, GTRI,