Near-infrared emitting Ca 5 (PO 4 ) 3 Cl:Eu 2+ ,Nd 3+ phosphor for modification of the solar spectrum.

Intense near-infrared (NIR) emitting phosphors Ca5 (PO4 )3 Cl:Eu2+ ,Nd3+ were synthesized using a conventional solid-state reaction method and characterized using X-ray diffraction, reflectance, photoluminescence (PL) emission and PL excitation (PLE) spectroscopy, and PL lifetime measurements. The emission could be excited by broad band radiation in the nUV region as a consequence of Eu2+ →Nd3+ energy transfer. The efficiency of Eu2+ →Nd3+ energy transfer was as high as 80.8%. Two components observed in the decay curves could be identified with Eu2+ substituting different Ca2+ sites. Eu2+ lifetimes were shortened after Nd3+ doping. Near infra-red emission intensity was limited by Nd3+ →Nd3+ energy transfer and the consequent concentration quenching. The critical distance for Nd3+ →Nd3+ energy transfer was estimated to be 11.41 Å. Absorption of nUV radiations followed by conversion to NIR indicated the potential application in solar photovoltaics.