Neodymium europium oxynitridosilicates of β-K2SO4 type: Structural, magnetic and red luminescence properties.

Rare earth activated nitridosilicates have important applications as phosphor components in white light emitting diodes. (Oxy)nitridosilicates with β-K 2 SO 4 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 NdEuSiO 3 N and the new oxynitridosilicate NdSrSiO 3 N by solid state reaction between Nd 2 O 3 , NdN, Eu 2 O 3 or SrO and Si 3 N 4 under N 2 /H 2 gas at temperatures of 1300 ​°C and 1500 ​°C respectively. These compounds are the limiting compositions of the solid solution NdSr 1-x Eu x O 3 N crystallizing in the space group Pmnb with cell parameters a ​= ​5.62293(1), b ​= ​7.02285(1) , c ​= ​9.64784(2) Å for NdEuSiO 3 N, and a ​= ​5.63074(9), b ​= ​7.01658(10), c ​= ​9.65765(15) Å for NdSrSiO 3 N. The Nd3+and Eu2+ cations in NdEuSiO 3 N or Nd3+ and Sr2+ in NdSrSiO 3 N 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 NdEuSiO 3 N is ferromagnetic with T c ​= ​3 ​K, in contrast to NdSrSiO 3 N that shows antiferromagnetic interactions at low temperatures. The band gaps of NdEuSiO 3 N and NdSrSiO 3 N determined from diffuse reflection spectroscopy are 2.37 and 3.72 ​eV respectively. NdEuSiO 3 N and the members of the solid solution NdSr 0.98 Eu 0.02 SiO 3 N and NdSr 0.5 Eu 0.5 SiO 3 N 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. β-K 2 SO 4 type NdEuSiO 3 N and the new oxynitridosilicate host NdSrSiO 3 N activated with Eu2+ show orange-red luminescence under excitation at 405 ​nm. [Display omitted] • Synthesis of the new oxynitridosilicate NdSrSiO 3 N and the solid solution NdSr 1-x Eu x SiO 3 N (0 ​≤ ​x ​≤ ​1) with β-K 2 SO 4 structure. • -Nd3+ ions preferentially occupy the 9th-coordinated sites whereas Sr2+ and/or Eu2+ prefer the 10th-coordinated sites. • NdEuSiO 3 N is ferromagnetic below 3 ​K whereas NdSrSiO 3 N shows antiferromagnetic correlations at low temperature. • NdEuSiO 3 N and NdSrSiO 3 N:Eu compounds are orange-red luminescent materials under excitation at 405 ​nm. [ABSTRACT FROM AUTHOR]