The tate of cooling ahers the luminescent properties (absorption, speetral emission and emission intensity) of halophosphate phosphors in characteristic and reversible manner. The Mn emission ehanges in both position and intensity, the Sb emission only in intensity, and the changes of both ate dependent upon the nature of the halide. Interpretation of x-ray diffraetion patterns, together with the luminescence results, leads to eonclusions regarding the probable position of the halide, Mn and Sb atoms in the lattice.Improvements in composition and preparation technique for calcium halophosphate phosphors have led to substantial increases of fluorescent lamp efficiencies during the last decade. Measured quantum efficiencies, however, indicate a probably significant margin left for potential further improvement. Comparison with simpler, more efficient phosphor systems raises the question whether sensitized phosphors, of which the halophosphates represent the outstanding prototype, ate inherently less efficient, of whether they ate amenable to still greater improvement through preparative modifications.Recognition of this problem has led to several fundamental investŸ gations of the system, with the aim to better understand its structural details and the conditions responsible for efficient absorption and excitation. One of these studies, to be reported here, was concerned with the effect which the cooling tate has upon the luminescence of halophosphates.Prefired phosphors were filled into the annular space of cylindrical, Dewar-type silica vessels which could be plugged of evacuated and sealed off as needed. The phosphors were then reheated at different temperatures for different lengths of time, after which they were cooled at three different rates: very fast ("quenched"), moderately fast, and slowly (the times to reach 500 ~ C from about 1100 ~ C were roughly 12, 200, and 9000 seconds, respectively, as determined with a fast-recording thermocouple imbedded in 4 mm thick powder charges).Prefired phosphors were chosen for two reasons: (1) to obviate any chemical of pressure difficuhies due to liberation of gases of interaction with air in reheating, and (2) to study strictly the effect of coolirtg rate independently of the kinetics of phosphor formation. To achieve "quenching", the firing vessels were plunged into water immediately upon their removal from the furnace. Acta P¡Ht~ng.
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