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Pressure Effects in Luminescence. Part II. Isobaric Experiments on NaI(Ti)

Report Number: AFOSR-TN-69-6
Author: Reiffel, L.
Corporate Author: Illinois Inst. of Tech. Armour Research Foundation
Date of Publication: 1959-02-02
Pages: 26
Contract: AF 49(638)113
AD Number: AD0208302
Original AD Number: AD 208302

The effect of steady-state hydrostatic pressure on the properties of luminescent systems, with particular reference to the phosphorescence of NaI(Ti), is examines. It is shown that readily observable changes in decay mean life may be produced by very modest pressures. An interpretation of these effects is developed from a configurational coordinate model and also from thermodynamic considerations. Experimental results are in good agreement with these theoretical expectations. for a 0.66-ev trap in NaI(Ti), the change in center volume at the point of transition from metastable to emitting state is found to be + 17.5 X 10^-24 cm^3. Assuming a specific model for the center allows computation of the sign and magnitude of the critical displacement of ions required for trap collapse - in this case +0.19A. The force constant for the metastable state is computed to be 5.8 X 10^5 dynes/cm; and the vibrational frequency, assuming an effective mass equal to six I negative ions, is 3.4 X 10^12 sec^-1 corresponding to a zero point energy for this trap of 0.007 ev and cross over at a vibrational quantum number of about 47. The transmission coefficient for the cross-over to the emitting state appears to be of the order of 0.03 per cent. Other possible experiments involving steady-state or transient pressure effects are outlined.

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