Thermal quenching of Ce³⁺emission in PrX₃(X = Cl, Br) by intervalence charge transfer

Abstract

The cause of the relatively low scintillation light yield of PrBr 3 :Ce 3+ is investigated by means of optical spectroscopy, the temperature dependence of scintillation properties and the temperature dependence of optically excited decay curves of undoped and Ce 3+ -doped PrCl 3 and PrBr 3 . The integrated intensity of x-ray excited luminescence of PrBr 3 :5% Ce 3+ shows that the light yield at room temperature (RT) is two times less than at 80 K. The decay time of Ce 3+ emission optically excited to its 5d band in PrBr 3 :5% Ce 3+ has a single exponential decay of 11.0 ± 1.1 and 6.0 ± 0.6 ns at 10 K and RT, respectively. It is proposed that Ce 3+ emission is quenched by a metal-to-metal charge transfer of Ce 3+ + Pr 3+ → Ce 4+ + Pr 2+ followed by 4f → 4f emission of Pr 3+ which is strongly concentration quenched.

Charge transfer transitions in the excitation spectra of PrX3:Ce3+ (X=Cl, Br) scintillators

“…As previously mentioned, in Ref. [1], the band at 216 nm (46,296 cm À1 ) is associated with the lowest energy Pr 3+ 4f 2 -4f 1 5d 1 excitation transition. However, the analysis presented above suggests that the Cl À -Pr 3+ CTT is also expected in the same wavelength region.…”

“…In the low-temperature excitation spectrum of PrCl 3 :Ce 3+ , a broad-band peak near 216 nm (46,296 cm À1 ) is observed while monitoring the interconfigurational emission transition of the Ce 3+ ion (l em ¼ 336 nm) [1]. This band is also observed in the excitation spectrum while monitoring the intraconfigurational Pr 3+3 P 0 -3 H 4 transition (l em ¼ 490 nm).…”

“…By using an empirical relationship, which pertains to the difference between the lowest energy Ce 3+ 4f 1 -5d 1 and Pr 3+ 4f 2 -4f 1 5d 1 excitation transitions, the authors of Ref. [1] have associated this band with the lowest energy Pr 3+ 4f 2 -4f 1 5d 1 excitation transition. However, as discussed below, the Cl À -Pr 3+ CTT can also be expected in the same wavelength region so that an unambiguous assignment of this band to the Pr 3+ 4f 2 -4f 1 5d 1 transition is not possible.…”

“…In the low-temperature excitation spectrum of PrBr 3 :Ce 3+ , a broad-band peaking near 240 nm (41,666 cm À1 ) is observed when the Ce 3+ emission is monitored (l em ¼ 380 nm). This band is associated with the Br À -Pr 3+ CTT [1]. The presence of the CTT band in the excitation spectrum of PrBr 3 :Ce 3+ remains unexplained in Ref.…”

“…The excitation and emission spectra of PrX 3 :Ce 3+ (X ¼ Cl, Br) scintillators has been published in a recent paper [1]. In this short communication two aspects of the excitation spectra are examined.…”