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Both time-resolved and steady-state spectroscopic techniques were used to investigate the mechanisms responsible for both the observed increase in luminance and the red shift of the emission frequency that occurs when Ga is introduced during the growth of SrS:Ce 3+ films. We compared the excitation spectra of SrS:Ce 3+ films prepared without Ga to SrS:Ce 3+ and SrS:Pr 3+ ,Ce 3+ films prepared with Ga. In addition, we also studied praseodymium-doped thin films to probe the local environment of the rare-earth ion in these materials. Finally, the implications of these results on the electroluminescent (EL) efficiency will be discussed.

Gallium codoping has been identified as an effective flux agent for SrS:Ce phosphor thin films. When rapid-thermal-annealed at temperatures above 750°C, the microstructure of sputtered SrS:Ce,Ga,F thin films underwent a transformation from columnar to spherulitic morphology. In addition, the crystal grain size increased by tenfold from 50 to 500 nm. Time-resolved photoluminescent measurements on 810°C-annealed SrS:Ce,Ga,F films showed decay times as long as 25 ns, indicating effective incorporation of Ce ions. As a result of crystallinity improvement, excellent electroluminescent performance, e.g., 60-Hz L 40 of 155 cd/m 2 , has been achieved in EL devices with 1.5-μm-thick SrS:Ce,Ga,F films. In addition, high luminous efficacy, e.g., e 40 = 1.15 Im/W, was achieved in devices with a thin SiON buffer layer added between the SrS:Ce and a BaTa 2 O 6 top insulator.

Results on fluorescent transient and photoconductivity measurements in Ce 3+- doped thiogallate materials are presented. Lifetime measurements were performed using a combination of time-resolved photon counting and laser techniques on both cold-pressed powder and melt-grown crystal materials. The photoconductivity measurements were performed on the melt-grown crystal at both room and liquid-nitrogen temperatures.

The study of phosphor materials generally focuses on systems with a high quantum efficiency. On the other hand, a thorough understanding why certain systems show very low quantum yield will certainly lead to a better understanding of phosphor materials in general. Here we present studies on cerium-doped lutetium oxide and yttrium oxide crystals that are characterized by a complete quenching of the 4f-5d luminescence. To find the origin of the quenching mechanism, as well as to understand the difference to other Ce 3+ systems with high quantum efficiencies, we have performed extensive absorption, photoexcitation, and photoconductivity studies on single crystals of these systems, prepared by the laser-heated-pedestal growth technique. It is experimentally verified that the quenching mechanism is determined by the location of the first excited level of the cerium ions with respect to the conduction band - a general result that can be applied to a broad range of materials and will allow us to characterize and engineer future phosphor materials.

Y 2 O 3 :Eu 3+ has been extensively investigated as a red phosphor for fluorescent lamps and color displays. In particular, there have recently been several studies examining the effect of impurities on the luminescence efficiency for Y 2 O 3 :Eu 3+ under UV excitation. In this work we investigate the effects of codoping Y 2 O 3 :Eu 3+ with Ca 2+ and Zr 4+ on the emission produced by cathode-ray excitation. Specifically, we have measured the relative efficiency, fluorescent lifetimes, and fluorescent spectra under cathode-ray excitation and compare these results to those previously observed under UV excitation.