Ion size effects on thermoluminescence of terbium and europium doped magnesium orthosilicate

Abstract

Thermoluminescence (TL) and radioluminescence (RL) are reported over the temperature range 25-673 K from MgSiO 4 :Tb and MgSiO 4 :Eu. The dominant signals arise from the transitions within the Rare Earth (RE) dopants, with limited intensity from intrinsic or host defect sites. The Tb and Eu ions distort the lattice and alter the stability of the TL sites and the peak TL temperature scales with the Tb and Eu ion size. The larger Eu ions stabilize the trapped charges more than for the Tb, and so the Eu TL peak temperatures are ;20% higher. There are further size effects linked to the TL driven by the volume of the upper state orbitals of the rare earth transitions. For Eu the temperatures of the TL peaks are wavelength dependent since higher excited states couple to distant traps via more extensive orbits. The same pattern of peak temperature data is encoded in RL during heating. The data imply that there are sites in which the rare earth and charge stabilizing defects are closely associated within the host lattice, and the stability of the entire complex is linked to the lattice distortions from inclusions of impurities.

Factors controlling the thermoluminescence spectra of rare earth doped calcium fluoride

“…However, in closely linked sites electron tunneling would initially favour the lower level transitions, as seen in this Er data. The same possibility has recently been reported for Tb and Eu doped magnesium orthosilicate dosimeters [34,35] and a more general review includes examples from crystalline material [36]. The possibility of such tunneling has frequently been discussed but these RE emission spectra produce TL that offers direct evidence.…”

Spectral changes and wavelength dependent thermoluminescence of rare earth ions after X-ray irradiation

“…This clarity of separation of peak temperature with increasingly higher starting levels of the Er occurs because all the transitions are from higher levels down to a single ground state (i.e. in contrast with say the Tb and Eu data discussed earlier) [15]. From the modelling of Fig.…”

“…The changes are not random but, as shown below, are linked to the higher-energy states of the ions that define the emission wavelength. Two clear examples of this effect are apparent in the spectra of TL from terbium or europium doped magnesium orthosilicate dosimetry powder [15]. Conceptually, these are not ideal examples as the dosimetry powders are sensitive to dopant concentration and their thermal processing.…”

Competing roles of defects in SrAl2O4:Eu2+,Dy3+ phosphors detected by luminescence techniques

“…3(b). Visual inspection of the collected data in terms of wave length (k) offers I(k)dk versus k. This is not ideal as the science requires an energy view of I(E)dE versus E. 17 Invariably the wave length presentation is distorted and broadened at longer wavelengths. In the energy domain plot, the true band is symmetric, as shown by the transformation to the energy plot of Fig.…”

“…Previous studies have indicated that collecting the TL spectra at low temperature adds considerably by both monitoring the intrinsic defects [16][17][18][19] and revealing the presence of inclusions. Similarly, radioluminescence (RL), obtained during heating whilst exciting the materials with x-rays, discloses a range of imperfections that may not be evident in the more limited TL data.…”