New Observations on the Pressure Dependence of Luminescence from Eu²⁺-Doped MF₂ (M = Ca, Sr, Ba) Fluorides

Abstract

The luminescence from Eu(2+) ions in MF2 (M = Ca, Sr, Ba) fluorides has been investigated under the pressure range of 0-8 GPa. The emission band originating from the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) ions in CaF2 and SrF2 shows the red-shift as increasing pressure with pressure coefficients of -17 meV/GPa for CaF2 and -18 meV/GPa for SrF2. At atmospheric pressure, the emission spectrum of BaF2:Eu(2+) comprises two peaks at 2.20 and 2.75 eV from the impurity trapped exciton (ITE) and the self-trapped exciton (STE), respectively. As the pressure is increased, both emission peaks shift to higher energies, and the shifting rate is slowed by the phase transition from the cubic to orthorhombic phase at 4 GPa. Due to the phase transition at 4-5 GPa pressure, the ITE emission disappears gradually, and the STE emission is gradually replaced by the 4f(6)5d(1) --> 4f(7) transition of Eu(2+). Above 5 GPa, the pressure behavior of the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) in BaF2:Eu(2+) is the same as the normal emission of Eu(2+) in CaF2 and SrF2 phosphors.

Cathodoluminescence and Raman Spectroscopic Analyses of Nd- or Yb-Doped Y2O3 Transparent Ceramics

“…33 In the meanwhile, the pressure dependence of luminescence bands from RE ions have shown that the emission band originating from the RE ions exhibits a redshift, i.e., shifts to lower wavelength as the pressure increases. 34,35 Therefore, the variation of band shifts observed in the line scans by CL and Raman spectroscopy are consistent with each other, if one assumes that such shifts are both contributed to by residual stress.…”

“…A study of pressure dependence of the yttria phase has shown that an increase of pressure (compression) results in a shift of the Raman modes to higher wavenumber (e.g., a linear relationship with a slope of −3.3 cm –1 /GPa was found for the 377 cm –1 Raman band when the pressure is lower than 15 GPa) . In the meanwhile, the pressure dependence of luminescence bands from RE ions have shown that the emission band originating from the RE ions exhibits a red-shift, i.e., shifts to lower wavelength as the pressure increases. , Therefore, the variation of band shifts observed in the line scans by CL and Raman spectroscopy are consistent with each other, if one assumes that such shifts are both contributed to by residual stress.…”

Modification of luminescence spectra of CaF2: Eu2+

“…It may be interesting to note that Su et al (35) observed changes in PL spectra of Eu 2+ -doped alkaline earth fluorides subject to pressure. For CaF 2 , emission maximum shifted to about 443 nm at eight GPa and the half width also increased by about 0.05 eV.…”

Spectroscopic Characterization of Ca3Y2Si3O12:Eu2+,Eu3+ Powders in VUV-UV–vis Region

“…The presence of three sites may account for some enlargement of observed Stokes shift, yet its extraordinary large value (8960 cm –1 ) substantiates that the system in its excited state experiences much rearrangement before radiative relaxation occurs. Such characteristics are not typical for a regular d → f Eu 2+ luminescence and may suggest that in Ca 3 Y 2 Si 3 O 12 this emission possesses an anomalous nature. , Luminescence with similar characteristics was extensively investigated in fluoride hosts. − It was proposed that the anomalous emission occurs when the 5d emitting level of Eu 2+ locates just below the bottom of the conduction band. After excitation, autoionization takes place and the electron delocalizes over surrounding cations and finally gets trapped in a nearby defect.…”