Abstract
Rare earth activated nitridosilicates have important applications as phosphor components in white light emitting diodes. (Oxy)nitridosilicates with β-K2SO4 structure doped with Eu2+ are luminescent materials with emission wavelengths ranging from green to red under excitation with blue-UV light. Here we report the synthesis of isostructural NdEuSiO3N and the new oxynitridosilicate NdSrSiO3N by solid state reaction between Nd2O3, NdN, Eu2O3 or SrO and Si3N4 under N2/H2 gas at temperatures of 1300 °C and 1500 °C respectively. These compounds are the limiting compositions of the solid solution NdSr1-xEuxO3N crystallizing in the space group Pmnb with cell parameters a = 5.62293(1), b = 7.02285(1), c = 9.64784(2) Å for NdEuSiO3N, and a = 5.63074(9), b = 7.01658(10), c = 9.65765(15) Å for NdSrSiO3N. The Nd3+and Eu2+ cations in NdEuSiO3N or Nd3+ and Sr2+ in NdSrSiO3N show partial order in the two available crystallographic sites of coordination numbers 10 (M1) and 9 (M2), with strongly preferred occupancy of the larger divalent cations Eu2+ (77%) and Sr2+ (78%) for the M1 site, whereas the M2 site is preferred by Nd3+. Magnetic susceptibility measurements down to 2 K show that NdEuSiO3N is ferromagnetic with Tc = 3 K, in contrast to NdSrSiO3N that shows antiferromagnetic interactions at low temperatures. The band gaps of NdEuSiO3N and NdSrSiO3N determined from diffuse reflection spectroscopy are 2.37 and 3.72 eV respectively. NdEuSiO3N and the members of the solid solution NdSr0.98Eu0.02SiO3N and NdSr0.5Eu0.5SiO3N are orange-red light emitting luminescent materials, showing a broad emission band centered between 605 and 639 nm under excitation at 405 nm. These compounds are new phosphor materials with emission wavelengths shifted to the red with respect to the isostructural oxysilicates, which is induced by the introduction of nitride.
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