Embedding of electroluminescent ZnS : Cu phosphors in PMMA matrix by polymerisation of particle suspension in MMA monomer

Alternating current powder electroluminescent lamps (ACPELs) were produced by UV initiated polymerization of liquid methylmethacrylate (MMA) monomer containing a ZnS:Cu phosphor powder dispersion. This method is suitable for the formation of a compact and void-free polymer matrix that limits water diffusion thus preventing the consequent corrosion of particles and luminescence quenching. A lamp was built up by sticking aluminum and indium–tin oxide (ITO) electrodes by using the pre-polymerized MMA/ZnS:Cu dispersion as a UV-curable glue. Dispersions were prepared by mixing the dry powder with MMA monomer activated with 2% weight of the photoinitiator Ciba Irgacure 184 UV and by pre-polymerization under stirring with a 125 W mercury lamp. Due to the high content of powder necessary to produce a bright lamp (1:1 weight of ZnS:Cu in MMA), a high viscosity slurry obtained with a 30 min pre-polymerization was required to maintain suspended the large size (tenths of μm) commercial phosphors. The polymerization process as a function of the irradiation time was investigated by FT-IR on films prepared by sticking two NaCl windows. The intensity decrease of the CC band at 1640 cm−1 indicates that polymerization is complete after 10 min irradiation. Electrical and spectroscopic characterization of the lamp was performed by analysis of luminescence spectra and determination of the current flowing in the circuit at different feeding voltages and frequencies. This preliminary investigation shows that UV polymerization of phosphor/monomer dispersions is a promising route for an easy and cheap production of ACPELs.