In this work, three different classes of colour converting layers (CCLs) for the down-conversion of blue and green Organic Light Emitting Devices (OLEDs) have been developed. In Chapter 3, the dispersion of organic dyes into polymer matrices via solution processing and solid state methods is presented. Application of hybrid organic-inorganic fluorescent particles, composed of organic fluorescent molecules absorbed into porous supporting materials, is discussed in Chapter 4. This solution allows for the dispersion of the organic molecule into an otherwise non-miscible polysiloxane matrix and resulted in the discovery of unusual optical properties of one of the organic dye (fluorescein disodium salt). This peculiar emission has been studied in more detail during Chapter 5. In addition, the possible use of fluorescent nanodiamonds, produced by gamma radiation, as luminescent materials, has been investigated in Chapter 6.