High-Pressure Low-Temperature Optical Studies of BaWO₄:Ce,Na Crystals

Abstract

We report detailed optical studies of BaWO4:Ce and BaWO4:Ce,Na single crystals. The material does not emit any luminescence at ambient pressure under near-UV (325 nm) excitation. Efficient green light is emitted only at high pressure (HP) and low temperature (LT). The luminescence is of excitonic character, since the lowest Ce3+ 5d level is degenerate with the conduction band also under hydrostatic pressures. To explain these phenomena, absorption measurements were made together with powder X-ray diffraction (XRD) and confocal micro-Raman and Fourier transform infrared (FTIR) spectroscopy. Raman experiments confirm the existence of a metastable phase, induced by certain nonhydrostatic conditions, before the reversible transition at a high-pressure range above 9 GPa, where efficient photoluminescence (PL) occurs. Although the phase transition is reversible, it proceeds with a prominent hysteresis observed in luminescence and Raman experiments. FTIR focuses on the existence of Ce3+ multisites observed during LT measurements.

BaWO4:Ce Single Crystals Codoped with Na Ions

“…This is related to the location of Ce 3+ 5d levels in the conduction band of the material. The luminescence is strongly temperature quenched, with a relatively small activation energy of a few meV [19]. Although Ce 3+ does not show any emission centers, it contributes to the efficiency of exciton formation.…”

“…Although Ce 3+ does not show any emission centers, it contributes to the efficiency of exciton formation. It was observed in [19] that in crystals doped with Ce 3+ , the exciton emission intensity is higher than in pure crystals.…”

“…Only excitonic and defect centers luminescence in a range of 280 nm and 400-600 nm, respectively, have been detected. In a paper by Wlodarczyk et al [19], optical spectroscopy of the above crystals has been analyzed under different values of external pressure. The authors of reference 19 have concluded that the observed luminescence has an excitonic character, independent of applied pressure.…”

Gamma‐Ray Irradiation Assisted Polyacrylamide Gel Synthesis of Scheelite Type BaWO4 Phosphors and Its Colorimetric, Optical and Photoluminescence Properties

“…According to literature [17], the absorption spectra for the BaWO 4 phosphors can be converted into (αhν) 2 ∼ hν curve. The intersection point between the steepest slope of the curve and the abscissa is the optical band gap (Eg) value.…”

Theoretical Investigation of the EPR G-Factor for the Axial Symmetry Ce3+ Center in the BaWO4 Single Crystal

“…Its potential applications include stimulated Raman scattering [7], scintillators and X-ray phosphor [8]. The blue and green PL emissions of BaWO 4 are widely discussed for their importance in future optical applications [9][10][11]. The barium tungstate crystals (BaWO 4 ) can also be used as a material for designing all solid-state lasers, especially for a wide variety of pump pulse durations in Raman laser pulses [12,13].…”