Sensitization of Nd3+ near infrared emission in Ca2PO4Cl host

Novel and efficient near infrared (NIR) emitting phosphor, Ca2PO4Cl:Eu2+, Nd3+ was synthesized by conventional solid state reaction and characterized with X-ray diffraction, photoluminescence emission, photoluminescence excitation spectra and fluorescence decay measurements. When excited with 400 nm, the phosphor gives broadband emission at 450 nm, which corresponds to the allowed 5d -> 4f transition of Eu2+ and intense NIR emissions in the range 800-1400 nm, which are assigned to the characteristic I-4(9/2,11/2,13/2) transitions of Nd3+ ions. The dependence of visible and NIR emissions, lifetime and the energy transfer efficiency (eta(ETE)) were investigated in detail. The PLE and PL spectra along with donor decay curves obtained under pulsed excitation have been used to establish the energy transfer mechanism between Eu2+-Nd3+ ions. The Eu2+ -> Nd3+ energy transfer efficiency obtained from the Eu2+ lifetimes in the single doped and co-doped samples reaches up to 41%. The critical distance between Eu2+ and Nd3+ in Ca2PO4Cl host was calculated, as 11.68 angstrom. The Inokuti-Hirayama (I-H) model of sensitizer to activator energy transfer is applied in analysis of the non-exponential fluorescence decays of Eu2+-Nd3+ co-doped Ca2PO4Cl. From I-H curve fitting, it is inferred that the electric dipole-dipole interaction is the main process responsible for the energy transfer from Eu2+ -> Nd3+. The results indicate that sensitization of Nd3+ is possible via 4f-5d transition of Eu2+ in Ca2PO4Cl host.