The properties and application of a UV downconverting phosphor (coronene) to silicon charge coupled devices are discussed. Measurements of the absorption spectrum have been extended to below 1000 A, and preliminary results indicate the existence of useful response to at least 584 A. The average conversion efficiency of coronene was measured to be -20% at 2537 A. Imagery at 3650 A using a backside illuminated 800 X 800 CCD coated with coronene is presented.

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Phosphor coatings have long been employed in the detection of UV radiation.' With the interest in the use of silicon charge coupled device (CCD) imagers as the detector for the space telescope and other space-borne astronomical missions, a UV sensitive phosphor is desired the emission spectrum of which usefully matches the spectral response of the CCD. Such a phosphor would provide an unparalleled opportunity to image in the UV, the visible, and near IR wavelengths with the same detector. A recent study has suggested that coronene and sodium salicylate (which emit at 500 and 420 nm, respectively) are the most promising candidate phosphors. 2The potential of a third organic phosphor, liumogen, is the subject of this Letter. The use of coronene with a rear illuminated CCD detector has been recently reported.3 The emission peak of coronene at 500 nm represents a reasonable overlap with the sensitive region of the CCD spectral response. In addition, thin films of the phosphor have been shown not to degrade the imaging response of the CCD at visible and near IR wavelengths. The emission peak of liumogen is at 520 nm with a strong secondary peak around 560 nm 4 as shown schematically in Fig. 1. This represents a better match to the spectral response of the silicon CCD than coronene, and a much better match than sodium salicylate. Consequently, it was felt that a comparison of the response of coronene and liumogen would be useful.United Detector Technology pin photodiodes model 1ODP were used to evaluate the UV response of liumogen and coronene. The pin devices were preselected for nearly equal quantum efficiency in the neighborhood of 500 nm. To simulate the eventual use of the phosphor, the window of the package was removed, and the diodes were coated with a thin layer (0.025 mg/cm 2 ) of either coronene or liumogen:1600-2000 A in the case of coronene and 3600 A in the case of liumogen. The phosphors were deposited using an evaporative technique.3 Figure 2 presents the results of spectral response measurements on several coated devices. In the figure, the quantum efficiency of the detector/coating is presented as a function of incident wavelength from 121.6 nm (Lyman-a) to 460 nm. The measurements from 122 to 280 nm were performed at the University of Wisconsin at Madison using a Jarrell-Ash model 205 monochromator with a gas discharge source. An EMI 543-P-09-00 calibrated photodiode was used to measure the incident energy. Measurements between 320and 460 nm were performed in our laboratory using a 1000-W Xe source, a Schoeffel model GN 250-1 grating monochromator, and a calibrated Tektronix model J6504 probe to measure incident flux. The quantum efficiency of the phosphor coated diode was determined from the relationwhere 7 diode is the quantum efficiency of the device under test, T 1ref is the quantum efficiency of the reference detector, diode and 1 ref are the signal currents of the test device and reference diode, respectively. All measurements were performed at room temperature.As may be noted from Fig. 2 the c...

The design and performance of the Texas Instruments 800 x 800 CCD imagerkare described. This device is fabricated utilizing a three phase, three level polysilicon gate process. The chip is thinned to -8 pm and is employed in the rear illumination mode. Detailed measurements of device performance including dark current as a function of temperature, linearity, and noise are presented. The device is coated with a UV downconverting phosphor which allows imaging with the same device over an extremely wide optical bandwidth.