X-ray microradiographs of small biological objects, such as animals and plant materials at micrometric resolution, are currently performed by various methods, all of which are limited by the resolution or the dynamic range of the image detectors. Here a novel X-ray image detector is discussed, in which the previous limitations have been overcome. A film of lithium fluoride salt is used as a detector, in which the stored biological image is read by observing the optically stimulated visible luminescence of the active color centers, efficiently produced by the X-rays.

By studying the photoluminescence of Alq 3 films as a function of time exposure to open and dry atmospheres, it has been found that the emission intensity can be described in a meaningful physical way by four, and only four, exponential decays. If the morphological structure of the film is also taken into account, then it is deduced that the bulk of the film is composed of three different states of aggregation that have been called species 1, 2, and 3. This unexpected discovery opens new research scenarios in the basic and applicative aspects of the Alq 3 molecule.

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Recently, it has been shown that the photoluminescence ͑PL͒ of one Alq 3 film decays in air with four different constant times and spectral features, implying the existence of four different components of molecular aggregation. Now the same behavior has been confirmed by measuring in open and dry air the PL of films fabricated in different physical conditions, which influence to various degrees the amplitude of the components. Moreover, the constant times are longer in Alq 3 films kept in the external dry environment than in the normal atmosphere. The implications of these experimental observations for the morphology of the films is discussed in the light of a phenomenological approach which has been called the four-components model.

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