Photoluminescence and energy transfer rates and efficiencies in Eu3+ activated Tb2Mo3O12

Abstract

Luminous efficacy (LE) and colour rendering index (CRI) of various simulated phosphor-converted warm white-light emitting diodes are calculated. Actual measured phosphor emission spectra are employed for this task. The efficacy and CRI of Eu3+ activated red emitting phosphors are superior to Eu2+ emitting nitride-based phosphors, however, Eu3+ suffers from low absorption strength in the blue spectral range. Tb3+ exhibits comparatively strong absorption in this range and can be used as a sensitizer for Eu3+. A solid solution series of (Tb1-xEux)2Mo3O12 (TM:Eu3+) powders and ceramic discs is prepared by conventional solid state synthesis. Complete transfer from Tb3+ to Eu3+ is achieved in the (Tb0.8Eu0.2)2Mo3O12 sample and a red colour point is realized upon 487 nm (Tb3+ 7F6 → 5D4) excitation with a quantum efficiency of 94%. Full conversion of a 380 nm LED and improved conversion of a 465 nm LED was achieved employing TM:Eu3+ ceramics. The position and temperature related shift of the Eu3+ Stark sublevels is determined from temperature-dependent emission and excitation spectra. These spectra also reveal excited state absorption from thermally excited Eu3+ 7F1, 7F2 and 7F3 states. High-temperature measurements in the range of 350 to 800 K show a T0.5 of 627 K. Decay measurements exhibit a clearly visible rise time. A new method to determine energy transfer rates from rise time curves is developed. From the energy transfer rates the transfer mechanism and efficiency can be determined with a higher degree of confidence compared to methods based on luminescence intensities. This journal is