Luminescence quenching by photoionization and electron transport in a LaAlO3:Ce3+ crystal

Abstract

A combined photoconductivity, absorption, and thermoluminescence study was performed to understand the absence of luminescence from Ce 3+ in LaAlO 3 :Ce 3+ . It is demonstrated that the absence of luminescence is the result of Ce 3+ ionization from the 5d excited states, which are all located in the conduction band. Ce 3+ ionization is accompanied by the formation of several broad absorption and photoconductivity bands, which are assigned to electron traps. A time and temperature dependent optical investigation of these traps reveals the conditions under which electrons are transferred from Ce 3+ to traps and vice versa, from traps back to Ce 4+ . The observed difference in energy needed to thermally or optically release electrons from traps is qualitatively explained in terms of the location of the ground and excited states of the electron traps with respect to the conduction band.

New localized/delocalized emitting state of Eu2+ in orange-emitting hexagonal EuAl2O4

“…A typical TL spectrum contains an asymmetric broadband ranging from 90 to 290 K and peaking at ~135 K, indicating that the traps are distributed over a wide range of energies below the host conduction band in h -EAO. According to previous studies202122, the delocalization energy of the excited electron at 77 K can be determined from the TL creation spectrum, i.e., the plot of TL integrated intensities versus the illumination wavelengths, as shown by the red ball curve in Fig. 3b (Note that the effect of thermally activated ionization is eliminated at 77 K).…”

“…3b also contains a higher energy threshold at ~420 nm. The strong electron delocalization in the high-energy region (i.e., 320−420 nm) can be attributed to the autoionizing intermediate states, i.e., the autoionization of 4 f 6 5 d states lying in the host conduction band202122.…”

Effects of heat treatment and UV irradiation on the transition metal impurities in LaAlO<inf>3</inf>

“…It is clearly shown that the optical absorption is increased by the irradiation of UV photons, and decreased by the irradiation of visible light. In the paper that reported a similar increase in absorption induced by UV photon irradiation, the increased absorption was divided into several components [2]. In the present research, it is assumed that the absorption increase by the irradiation of UV photons can be divided into four Gaussian components with peaks at 2.7, 3.5, 4.0, and 4.5 eV, as shown in Fig.…”

Fabrication and luminescent properties of Ce:LaAlO3 translucent ceramics

“…However, in 2007, Kolk et al published a paper about photoconduction evaluation of Ce:LaAlO 3 [9]. In Kolk's paper, they concluded that Ce 3+ emission did not occur in Ce:LaAlO 3 due to the photoionization.…”