Near‐infrared emitting Ca5(PO4)3Cl:Eu2+,Nd3+ phosphor for modification of the solar spectrum

Abstract Intense near‐infrared (NIR) emitting phosphors Ca 5 (PO 4 ) 3 Cl:Eu 2+ ,Nd 3+ 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 Eu 2+ →Nd 3+ energy transfer. The efficiency of Eu 2+ →Nd 3+ energy transfer was as high as 80.8%. Two components observed in the decay curves could be identified with Eu 2+ substituting different Ca 2+ sites. Eu 2+ lifetimes were shortened after Nd 3+ doping. Near infra‐red emission intensity was limited by Nd 3+ →Nd 3+ energy transfer and the consequent concentration quenching. The critical distance for Nd 3+ →Nd 3+ 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.