Luminescence of Eu2+ Ions in CsMgPO4 Phosphor: Anomalous Emission and its Origin

Abstract

Eu 2þ -doped CsMgPO 4 phosphors were synthesized by the conventional high-temperature solid-state reaction. The phase formations of the phosphors were confirmed by X-ray powder diffraction measurements. The photoluminescence excitation and emission spectra, the temperature dependent (10-300 K) luminescence intensities and the decay curves of the phosphor were measured. The Eu 2þ -doped CsMgPO 4 shows a red emission band peaking at around 650 nm from 4f 6 5d 1 !4f 7 transitions of Eu 2þ ions. The luminescence nature of CsMgPO 4 :Eu 2þ is greatly different from the other Eu 2þ doped ABPO 4 orthophosphates (A and B are mono-and divalent cations, respectively) and is characterized by the red-shifted emission, the larger Stokes shift and a lower luminescence quenching temperature. The anomalous luminescence properties of CsMgPO 4 :Eu 2þ are ascribed to impurity trapped exciton emission.

Origin and Luminescence of Anomalous Red-Emitting Center in Rhombohedral Ba9Lu2Si6O24:Eu2+ Blue Phosphor

“…33 Thus, the ETE emission exhibits properties of a large Stokes shift and a low thermal stability, 36−40 such as in Sr 4 Al 14 O 25 :Eu 2+ , 33 BaF 2 :Eu 2+ , 36 and CsMgPO 4 :Eu 2+ . 40 In the present case for BLS:Eu 2+ , the coordination number for Ba(1) (12-fold) is higher than that for Ba(2) (9-fold) or Ba(3) (10-fold). Thus, it should be easy to understand that the ETE comes from the Ba(1) site.…”

“…Usually, the ETE state is lower than the normal 4f 6 5d 1 energy level of Eu 2+ . Thus, the ETE emission exhibits properties of a large Stokes shift and a low thermal stability, − such as in Sr 4 Al 14 O 25 :Eu 2+ , BaF 2 :Eu 2+ , and CsMgPO 4 :Eu 2+ . In the present case for BLS:Eu 2+ , the coordination number for Ba(1) (12-fold) is higher than that for Ba(2) (9-fold) or Ba(3) (10-fold).…”

Luminescent characteristics of Eu2+/Li+ doped (La-Al)2O3 phosphors and PMMA films activated with them

“…%) phosphor, with an excitation wavelength of 297 nm and luminescence wavelength of 440 nm were fitted by a double exponential decay model with τ 1 = 592 ns, f 1 = 0.9819 and τ 2 = 29 ns, f 2 = 0.0181; and a χ 2 = 1.185. These values are comparable to previously reported values for Eu 2+ in another host material [36][37][38], it is known that the d-f transition of Eu 2+ is parity and spin allowed with a lifetime on the order of sub-microseconds [39,40]. Figure 6 shows the cathode-luminescence (CL) spectra for (La-Al) 2 O 3 :Eu 2+ (5at.%) and (La-Al) 2 O 3 : Eu 2+ (5at.%) /Li + (4.5 at.…”

Anomalous Trapped Exciton and d–f Emission in Sr4Al14O25:Eu2+

“…It is observed more frequently for Eu 2+ on sites with a high coordination number . The ETE is described as a state in which the Eu 2+ ion is ionized to Eu 3+ and the electron is stabilized in the vicinity by delocalization over the neighboring cations. − If the crystal field splitting for the 5d state is small (e.g., due to a high coordination number) the ETE state can be situated below the 4f 6 5d state and ETE emission occurs. The most famous example is BaF 2 :Eu 2+ , which shows a broad yellow ETE emission band at low temperatures .…”

“…The peculiar shift of the 425 nm emission band with temperature can be explained by temperature induced transition from Eu 2+ trapped exciton to 4f 6 5d Eu 2+ emission. Mostly for Eu 2+ 4f 6 5d emission is observed, but ETE emission has been reported in a variety of host lattices. − The observation of ETE has been reviewed by Dorenbos and is characterized by a large Stokes shift and low quenching temperature. It is observed more frequently for Eu 2+ on sites with a high coordination number .…”