Synthesis and luminescent properties of Eu3+- and Eu2+-activated sodium pyrophosphate Na4P2O7

Abstract

The luminescent properties of Eu 3+ and Eu 2+ ions in sodium pyrophosphate, Na 4 P 2 O 7 , have been studied. The excitation spectrum of the Eu 3+ emission in Na 4 P 2 O 7 consists of several sets of bands in the range 280-535 nm due to 4f-4f transitions of Eu 3+ ions and a broad band with a maximum at about 240 nm interpreted to be due to a charge transfer (CT) transition from oxygen 2p states to empty states of the Eu 3+ 4f 6 -configuration. Although the CT band energy is large enough, the quantum efficiency (η) of the Eu 3+ emission in Na 4 P 2 O 7 under CT excitation was estimated to be very low (η ≤ 0.01). In terms of a configurational coordinate model, this fact is interpreted as a result of the high efficiency of a radiationless relaxation from the CT state to the 7 F 0 ground state of Eu 3+ ions occupying sodium sites in Na 4 P 2 O 7 . A strong reducing agent is required in order to stabilize Eu 2+ ions in Na 4 P 2 O 7 during the synthesis. Several nonequivalent Eu 2+ luminescence centers in Na 4 P 2 O 7 were found. Keywords: sodium pyrophosphate, Eu 3+ and Eu 2+ ions, luminescence, quantum efficiency.Introduction. Luminescence of lanthanide ions in alkali-metal phosphates has not been reported despite the comparatively large number of publications on the latter. Such information seems useful for interpreting the luminescent properties of lanthanide ions in double alkali and alkaline-earth phosphates of general formula M