Explaining the decline in the yield of luminescence after surpassing a phase of saturation as the dose of stimulation continues to increase

Introduction:

The time-course of the luminescence of a material after stopping the stimulating radiation characterizes the life-time of the radiative transitions that are converted after stimulation. And the yield of luminescence increases as the dose of stimulation increases, until reaching a saturation phase. Several experiments since 1993, however, have revealed that as the stimulation dose exceeds a saturation level, the luminescence yield may decline. And there is a lack of modelling-based understanding of this phenomenon. This work aims to present a model that may help understand the post-saturation decline of the luminescence yield.

Methods:

Spatially resolved delayed luminescence from yeast irradiated by ultraviolet-containing intense light was acquired by using a cooled CCD over a fixed duration (100 seconds) of exposure post photo-stimulation. The duration of the photo-stimulation varied over six orders of magnitude, from 1 millisecond to 1000 seconds. By using an irradiation–integration interleaved method [Piao, 2024], the yield of delayed luminescence of the yeast as a function of the irradiation dose was acquired in a total of five measurements. The dose–response of the yield of delayed luminescence consistently revealed a decline after saturation that is not explained by the common model of delayed luminescence. We propose a modification to the common three-level model of delayed luminescence to explain the post-saturation decline.

Results:

The decline in the integrated delayed luminescence observed by our measurements is equivalent to the decline in the commonly measured starting amplitude of the delayed luminescence commonly measured. By setting a limit to the number of the material’s atomic states that can be stimulated towards delayed luminescence, the common three-level model approach can lead to a reduction in the starting amplitude of the delayed luminescence after all pumpable states have been exhausted by the pumping dose.

Conclusions:

A model is proposed for the post-saturation decline of the luminescence yield of yeast. The insights may be relevant to pump-probe applications.