Elucidating white light emissions in Tm3+/Dy3+ codoped polyoxometalates: a color tuning and energy transfer mechanism study

Abstract

The double-tartaric bridging Tm-substituted POM derivative [N(CH₃)₄]₆K₃H₇[Tm(C₄H₂O₆)(α-PW₁₁O₃₉)]₂·27H₂O (1) was successfully synthesized and well characterized by various physico-chemical analyses. Furthermore, the mixed Dy³⁺/Tm³⁺ ion-based POM derivatives [N(CH₃)₄]₆K₃H₇[Dy_xTm_1−x(C₄H₂O₆)(α-PW₁₁O₃₉)]₂·27H₂O (3–8) were first synthesized and confirmed by PXRD and IR spectra, indicating compounds 3–8 are isomorphic with 1. The detailed analyses of Ln–O–W bond angle and coordinated aqua ligands around emitting Ln³⁺ ions have revealed that the mentioned negative factors do not effectively affect the luminescence of emitting Ln³⁺ ions in 1–8. Investigations of PL emissions reveal that 3–8 can display color-tunable PL properties, emitting color from blue to white to yellow. The study of time-resolved emission spectroscopy of 6 indicates the energy can transfer from the LMCT excited state of POM fragments to Tm³⁺ and/or Dy³⁺ ions. Furthermore, the decreased luminescent lifetime of Tm³⁺ ions in 3–8 reasonably verifies the energy transfer from Tm³⁺ to Dy³⁺ ions to efficiently facilitate emissions of the Dy³⁺ centre.