Luminescence principles approximation

Therefore, the emitting species M and M L can in principle be identified from a decomposition of the total emission spectrum, and thus TRES experiments are mainly based on the evaluation of emission spectra rather than luminescence decays. However, a detailed analysis of the decays allows one to derive important information that cannot be obtained through the emission spectra, as will be explained below. In the frame of model 2, it is easily shown that the expressions of the relative contributions of the two species to the global emission spectrum contain only one unknown parameter, Afapp, while the equivalent expressions under the frame of model 1 are much more complex. This raises the question as to whether model 2 can be considered a reasonable approximation of the more complex scheme 1. This issue can be discussed qualitatively on the basis of three distinct cases of model 1, depending on the importance of photochemical reactions. 

Initially, the PL mechanism is mainly studied by the molecular orbit theory, and this theory only treats some high-symmetry crystal. For intrinsic PL materials, first-principles calculations are used extensively to discuss the PL origin. From the calculation result, the fundamental crystal information and electronic properties can be obtained. The electronic-transition modes and their allowed or forbidden transition nature can be revealed. Thus, the theoretical results can predict the excitation and emission band positions approximately, which helps to perform the band assignment in the experimental spectra. After knowing the luminescent mechanism, we can modify the luminescence intensify and shift peak position as well as broaden the emission ranges by utilizing various experimental strategies. 

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