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In spite of the crucial role it is believed to play in nature, fluorescence in natural organisms remains under-investigated from optical, chemical and biological perspectives. One example is the transparent wings of insects from the order Hemiptera: fluorescence emission has so far not been reported in any of the 3,000 described species of the superfamily Cicadoidea. The phenomenon has however been investigated in several butterfly and moth species, in which the coloured wing scales are known to embed fluorophores such as papiliochrome II. Photonic structures present in these scales may mediate the associated light emission. Fluorescence has also been described in the vein joints and the membrane of the transparent wings of damselflies and dragonflies. This emission was attributed to the presence of autofluorescent proteins such as resilin that gives rise to low stiffness and high strain in the biological tissues, allowing passive wing deformations. In this article, we characterised the fluorescence emission from the transparent wings of the grey cicada \textit{Cicada orni} (Linnaeus, 1758) and the common cicada \textit{Lyristes (Tibicen) plebejus} (Scopoli, 1763), using linear and nonlinear optical methods. We compared their properties with the fluorescence emission from two other insects exhibiting transparent wings, namely, \textit{Hemaris fuciformis} (Linnaeus, 1758) commonly known as the broad-bordered bee hawk-moth and the Bornean damselfly \textit{Vestalis amabilis} Lieftinck, 1965. These fluorescent behaviours were optically characterised by one- and multi-photon microscopy and spectrometry, allowing us to infer the symmetry of the material as well as the biological role of the fluorophores in the visual perception of insects and to explain the high absorption by the material in the range 300-400~nm., Comment: 16 pages, 6 figures, 1 table

A series of single-molecule dysprosium (Dy 3+) complexes consisting of b diketonate ligands, as water-containing complexes, and the auxiliary triphenylphosphine oxide (tppo)ligand as water free complexes were investigated as potential white light emitters. The coordination environment and choice of the ligands play an important role in the behavior of the yellow and blue emission of the Dy 3+ complexes based on the sensitization efficiency of the Dy 3+ ion by the ligands. By introducing the auxiliary tppo ligand in the complex, the relative intensity of the Dy 3+ emission increases due to a more efficient sensitization of the Dy 3+ ion.

Upon illumination by ultraviolet light, many animal species emit light through fluorescence processes arising from fluorophores embedded within their biological tissues. Fluorescence studies in living organisms are however relatively scarce and so far limited to the linear regime. Multiphoton excitation fluorescence analyses as well as non-linear optical techniques offer unique possibilities to investigate the effects of the local environment on the excited states of fluorophores. Herein these techniques are applied for the first time to the study of insects' natural fluorescence. The case of the male Hoplia coerulea beetle is investigated because the scales covering the beetle's elytra are known to possess an internal photonic structure with embedded fluorophores, which controls both the beetle's colouration and the fluorescence emission. An intense two-photon excitation fluorescence signal is observed, the intensity of which changes upon contact with water. A Third-Harmonic Generation signal is also detected, the intensity of which depends on the light polarisation state. The analysis of these non-linear optical and fluorescent responses unveils the multi-excited states character of the fluorophore molecules embedded in the beetle's elytra. The anisotropy of the photonic structure, which causes additional tailoring of the beetle's optical responses, is confirmed by circularly polarised light and non-linear optical measurements., Comment: 12 pages, 4 figures, 1 table, 1 SI file