The lowest triplet energy levels of the six ligands（T） were determined to be 22989 cm-1[1,3-bis-（1＇-phenyl-3＇-methyl-5＇-pyrazolon-4＇）-1,3-propanedione,BPMPTD],23148 cm-1[1,4-bis-（1＇-phenyl-3＇-methyl-5＇-pyrazolon-4＇）-1,4-butanedione,BPMPBD],23419 cm-1[1,5-bis-（1＇-phenyl-3＇-methyl-5＇-pyrazolon-4＇）-1,5-pentane-dione,BPMPPD],23310 cm-1[1,6-bis-（1＇-phenyl-3＇-methyl-5＇-pyrazolon-4＇）-1,6-hexanedione,BPMPHD],21978 cm-1[1,9-bis-（1＇-phenyl-3＇-methyl-5＇-pyrazolon-4＇）-l,9-nonanedione,BPMPND] and 21930 cm-1[1,10-bis-（1＇-phenyl-3＇-methyl-5＇-pyrazoion-4＇）-1,10-decanedione,BPMPDD],respectively.It was explained satisfactorily that the six ligands are more efficient for sensitizing the luminescence of Tb3＋ than that of Eu3＋ at room temperature,and the order of the luminescent intensities for the Tb3＋ complexes is explained by the relative energy gap between T and 5DJ of Tb3＋ or Eu3＋.As a conclusion,when 2700 cm-1＜△E（T-5D4）＜3000 cm-1,the luminescent intensity of the Tb3＋ complex is the strongest.This means that the lowest triplet energy level of the ligand is a chief factor to dominate RE3＋luminescence.
A new ligand, N,N-BIS (6-metyl-2-pyridinecarboxylamide-N-oxide)-1,2-ethane (L) and six lanthanide(Ⅲ) complexes (RE=La, Sm, Eu, Tb, Gd, Yb) were synthesized and characterized in detail. The results indicated that the composition of the binary complexes was determined as [REL(H2O)(NO3)2]NO3·nH2O (n=0-2), and the Eu3+ complex had bright red fluorescence in solid state. Three complexes of Eu3+, Tb3+, and Gd3+ with 6-methylpicolinic acid N-oxide (L’) were also synthesized. The relative intensity of sensitized luminescence for Eu3+ increased in the following order: L>L’. The phosphorescence spectra of the Gd3+ complexes at 77 K were measured. The energies of excited triplet state for the ligands were 20704 cm-1 (L) and 20408 cm-1 (L’). The facts that the ligands sensitized Eu3+ strongly and the order of the emission intensity for Eu3+ complexes were explained by ΔE(T-5D). This meant that the triplet energy level of the ligand was the main factor to influence RE3+ luminescence.
