Decay times, efficiencies, and spectral energy distributions of a number of Ce3+-aetivated phosphors have been determined. Decay times as short as 25-30 nsee are found for YPO4-Ce, YOC1-Ce, and YA13B4OI2-Ce; the two first-named phosphors show a weak, the last a strong, afterglow. The techniques of measurement have been described.Ce3+-activated phosphors are known as phosphors with very short decay times. The emission is ascribed to a 5d -> 4f transition in the Ce ~+ ion. The decay time is found to be shorter than 100 nsec due to the fact that an allowed transition is involved. Recently Ropp (1) summarized the results previously obtained and gave new data on Ce3+-activated rare earth phosphates. The decay times of the latter phosphors are about 30 nsec, i.e. shorter than reported previously for Ce z+ phosphors. Awazu and Muto (2) described sensitization of YPO4-Ce by the incorporation of thorium ions, leading to a higher photoluminescent efficiency.The emission band of Ce~+-activated phosphors has a doublet character due to the splitting (~2000 cm -1) of the ground state (2FT/2,2Fs/2). The emission is nearly always located in the blue or ultraviolet region of the spectrum. An exception is the yellow emission of the phosphor Y3A15012-Ce which has been recently described (3).In this paper, decay times, efficiencies, and spectral energy distribution of the emissions are given for several Ce 3 +-activated phosphors, especially yttrium, scandium, and lanthanum phosphates and borates and yttrium oxychloride.The cerium-activated phosphors find application in: (a) Flying-spot cathode-ray tubes for the TV transmission of films and slides. For color TV, an emission is required covering the whole visible spectrum. (b) A special type of color-TV receiving tube, the so-called index tube where an ultraviolet emitting phosphor is required in order to obtain the index signal (4). ExperimentalThe preparation of the phosphors has been described by us earlier (5). The cerium concentration is 1-2%.The decay times are measured both with ultraviolet and cathode-ray excitation. With cathode-ray excitation, a square pulse of voltage is displayed to the grid of the electron gun of a demountable cathode-ray tube, so that the phosphor can be irradiated during a variable time and with a variable repetition frequency. The method is analogous to that described previously by Bril and Klasens (4), but now much shorter times can be measured due to the use of a square-wave oscillator giving short pulses with a very short rise time (Tektronix Type 109, rise time 0.25 nsec, repetition frequency 550-720 pulses/sec) in combination with an oscilloscope with a wide frequency band (Philips No. 3330, bandwidth 70 MHz). The oscilloscope pictures were photographed with the aid of a Polaroid camera. To find all decay components, it is necessary to irradiate the phosphor with a wide range of excitation times in succession. Suppose a short and a long decay time component of equal efficiency are present, of e.g. 50 nsec and 1 msec. When the phosphor is then ir...

Three different types of radiationless transitions playa role in the radiationless decay of the luminescent Eu3+ center in LaAIO a : (a) a temperature-independent process from the charge-transfer state, (b) a temperature-dependent process (t..E=0.15 eV) from this state, (c) a temperature-dependent process (t..E= 1.1 eV) from the 5DO level. All three processes are of importance because the charge-transfer state of Eu3+ is situated at low energies in LaAIOa• If, however, this state is situated at higher energies, as it is in other host lattices, only process (b) will be observed in the conventional range of temperatures.

Efficiencies of various powder phosphors under x‐ray excitation are determined. Thin layers are used to minimize the loss in light output due to scattering and absorption of the emitted luminescence. The luminescence of the layer is measured with the aid of a calibrated photomultiplier. The absorbed x‐ray radiation is measured with a scintillation crystal. The efficiencies found are of the order of the cathode‐ray efficiencies; calcium tungstate has the largest deviation.