Synthesis And Luminescence Properties Of Nd³⁺ Doped C12A7 Powders

Nd³⁺ doped 12CaO·7Al₂O₃(C12A7:x%Nd³⁺)powders with different concentrations were synthesized by a self-propagating combustion method.Upon 808 nm excitation,there exist three peaks around 887,1069 and 1340 nm,which can be attributed to the 4F3/2→4IJ/2（J=9,11,13）transitions of Nd³⁺,respectively.When Nd³⁺ concentration is 0.7%,the strongest infrared luminescence emissions can be observed.Near infrared emission peaks exhibits a decreasing behavior with increasing Nd³⁺ doping concentration due to the concentration quenching effect.Based on the temperature-dependent emission spectra,the obtained thermal activation energy is about 161.6 me V,suggesting that C12A7: x%Nd³⁺powders possess good thermal stability.When as-prepared C12A7:0.5%Nd³⁺ powders were annealed at 1300 ℃ in H₂ atmosphere,the crystallinity of the sample increased.Meanwhile,the intensities of near infrared emission peaks of Nd³⁺ were enhanced with increasing the annealing time.After annealing in H₂ atmosphere,encaged OH-and H-concentrations and the grain size of C12A7 were increased and the cages were distorted.When the annealed sample was treated at 400℃ in air,the near infrared emission was further enhanced.Based on luminescence kinetics analysis,it is an efficient strategy for enhancing the near infrared emission through increasing the crystallinity of the sample in combination with decreasing the non-radiative transition rates.The obtained thermal activation energies of these samples are more than 110 me V showing its good thermal stability.When the as-prepared C12A7:0.5%Nd³⁺ powder were annealed at 1300 ℃ in O₂ atmosphere for hours,the near infrared emission was enhanced.However,with further increasing the annealing time,the decreased luminescence can be observed.Based on the luminescence kinetics analysis,it can be inferred that the following reaction happens described as O₂-（c）+ O₂（g）→O-（c）+ O₂-（c）.This resulted in the increased symmetry of the cage and the decreased radiative transition rate.Thus the weak luminescence can be observed.The thermal activation energy of the sample is about 123.5 meV,indicating that the annealed sample in O₂ atmosphere still have good thermal stability.The abovementioned experimental results suggest that C12A7 is a candidate host material for enhancing near infrared emissions of Nd³⁺ through controlling the sorts and amounts of encaged anions and the crystallinity of C12A7:Nd³⁺ powders,indicating that C12A7:Nd³⁺ has potential applications in the near-infrared detection and novel near infrared laser.