Near infrared excitation/emission imaging

Two-photon emission is a process in which electronic transition between quantum levels occurs through the simultaneous emission of two photons. [27] presents more details about two-photon emission. Since metal clusters emit in the near-infrared region, they can be made useful for two-photon imaging with infrared excitation. Two-photon emission of Au25 clusters is observed at 830 nm by exciting at... 

Phosphors. Infrared radiation can stimulate the emission of visible radiation from certain types of phosphors which have been previously excited by ultraviolet radiation. Becker and Risgin [2.71] have reported that self-activated ZnS crystals have exhibited both visible luminescence and photoconductivity when stimulated by radiation in the 1-3 pm interval. Geusic et al. [2.72] have shown that rare earth phosphors can convert very near infrared (0.93 pm) radiation into the visible with an efficiency as high as 1 %. Although phosphors can be employed to convert images directly, their lack of sensitivity has limited their usefulness. 

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