Luminescence and energy transfer phenomena in YVO4 single crystal co-doped with Tm3+ and Eu3+

Detailed spectroscopic investigation of YVO4:5 at% Eu3+, 1 at % Tm3+ single crystal encompassing analysis of absorption, excitation and time resolved emission spectra recorded at 5 K and 300 K made it possible to determine energies, intensities and bandwidths of transitions within 4fn configurations of trivalent thulium and europium. Transients recorded upon femtosecond pulse excitation made it possible to determine dynamics of population build-up and relaxation of excited states involved in luminescence phenomena. It was found that in YVO4:Eu, Tm system the metastable 5D0 level of Eu3+ and 1G4 level of Tm3+ can be populated by energy transfer from excited VO43− group and respective intra-ion relaxation processes from higher energy levels. Recorded excitation spectra of the 5D0 luminescence of Eu3+ and of the 1G4 luminescence of Tm3+ do not evidence the Eu3+↔Tm3+ energy transfer. Nevertheless, an examination of acquired luminescence decay curves, performed with reference to available information on relaxation dynamics of YVO4:Tm3+ system, reveals that the incorporation of Eu3+ accelerates decays of the 1G4 and 3H4 levels of Tm3+. Spectroscopic parameters characterising the donor-acceptor interaction involved in the 3H4 decay were evaluated applying the Inokuti-Hirayama model. Relevance of donor and acceptor transition peculiarities for energy transfer processes contributing to the 1G4 and 3H4 decays was assessed in the framework of phenomenological model proposed by Kushida and discussed. It was concluded that the intensity ratio of the blue 1G4 luminescence to orange-red 5D0 luminescence; hence the colour of visible emission in UV-excited YVO4:Eu3+, Tm3+ phosphor, may be adjusted by appropriate choice of Eu3+ and Tm3+ concentrations.