Photoluminescence excitation (PLE) and emission spectra (PL) of undoped (Sr, Ca)3(Y, Lu)2Ge3O12 as well as Eu3+- and Ce3+-doped samples have been investigated. The PL spectra show that Eu3+ enters into both dodecahedral (Ca, Sr) and octahedral (Y, Lu) sites. Ce3+ gives two broad excitation bands in the range of 200−450 nm. First-principle calculations for Ce3+ on both dodecahedral and octahedral sites provide sets of 5d excited level energies that are consistent with the experimental results. Then the vacuum referred binding energy diagrams for (Sr, Ca)3(Y, Lu)2Ge3O12 have been constructed with the lanthanide dopant energy levels by utilizing spectroscopic data. The Ce3+ 5d excited states are calculated by first-principles calculations. Thermoluminescence (TL) glow curves of (Ce3+, Sm3+)-codoped (Sr, Ca)3(Y, Lu)2Ge3O12 samples show a good agreement with the prediction of lanthanide trapping depths derived from the energy level diagram. Finally, the energy level diagram is used to explain the low thermal quenching temperature of Ce3+ and the absence of afterglow in (Sr, Ca)3(Y, Lu)2Ge3O12.@en

In this work it is shown that CaZnOS:Eu2+ has no Eu2+ emission even at low temperature. The observed and earlier reported red emission originates from a CaS:Eu2+ impurity phase. By means of washing the as-prepared samples with diluted nitride acid, we were able to remove the CaS impurity phase and study the Eu2+ emission in the pure CaZnOS phase. A clear relation was found between the red emission intensity, the CaS XRD line intensities and the nitric acid solution washing time, with zero intensity after prolonged washing. A so-called VRBE (vacuum referred binding energy)-diagram was constructed showing the energy of the 4fn and 4fn-15d1 states of the divalent and trivalent rare earth ions as dopants in CaZnOS with respect to the vacuum energy. This diagram shows that the 5d-levels of Eu2+ are located in the conduction band, which explains the absence of 5d→4f emission. By comparing the VRBE diagram with diagrams of other related compounds like CaO, CaS, ZnO and ZnS it becomes clear that the Eu2+ luminescence quenching is caused by a low lying conduction band, typical for Zn-based compounds.@en

Two different charge carrier trapping processes have been investigated in RE2O2S:Ln3+ (RE = La, Gd, Y, and Lu; Ln = Ce, Pr, and Tb) and RE2O2S:M (M = Ti4+ and Eu3+). Cerium, praseodymium and terbium act as recombination centers and hole trapping centers while host intrinsic defects provide the electron trap. The captured electrons released from the intrinsic defects recombine at Ce4+, Pr4+, or Tb4+ via the conduction band. On the other hand, Ti4+ and Eu3+ act as recombination centers and electron trapping centers while host intrinsic defects act as hole trapping centers. For these codopants we find evidence that recombination is by means of hole release instead of electron release. The released holes recombine with the trapped electrons on Ti3+ or Eu2+ and yield broad Ti4+ yellow-red charge transfer (CT) emission or characteristic Eu3+ 4f–4f emission. We will conclude that the afterglow in Y2O2S:Ti4+, Eu3+ is due to hole release instead of more common electron release.@en

In this thesis, two different charge carrier trapping and detrapping processes are investigated: (1) electron trapping and electron release; (2) hole trapping and hole release. Both of these two processes can be used to “deliberate design” afterglow phosphors or storage materials.@en

Trivalent Nd, Dy, Ho, Er, Tm, Sm and Eu usually act as electron trapping centers in wide band gap compounds, whereas trivalent Ce, Tb and Pr act as hole trapping centers. When a deep electron trap is combined with a shallow hole trap, then during the thermoluminescence glow the hole is released, generating recombination luminescence at the electron trap. However, in the case of a shallow electron trap, the electron will be released to recombine at the hole trapping center. With the knowledge of the location of the lanthanide levels within the band gap, one may engineer the depth of the electron trap, the depth of the hole trap, and where the recombination will take place. This has all been tested and verified for the lanthanides in GdAlO3 (Luo et al., J. Phys. Chem. C., 2016, 120, 5916). In this work, Cr3+ is combined with various trivalent lanthanides in GdAlO3. By combining thermoluminescence with optical spectroscopy data, a consistent interpretation of all the data is obtained. Cr3+ can act both as a deep electron trap and a deep hole trap, which is different to all of the lanthanides. From the results we can deduce the location of the Cr2+ and Cr3+ levels within the band gap and with respect to the vacuum level. Besides thermoluminescence recombination via the conduction band, evidence is found for athermal (tunneling) recombination. The results for GdAlO3 are compared with the results for LaAlO3. It was found that they are related systems but LaAlO3 has a lower lying conduction band and a higher lying valence band, which reduces the trap depths of the lanthanides and Cr in a predictive fashion.@en

Two different trapping and detrapping processes of chargecarriers have been investigated in GdAlO3:Ce3+,Ln3+(Ln = Pr, Er, Nd, Ho, Dy,Tm, Eu, and Yb) and GdAlO3:Ln3+,RE3+(Ln = Sm, Eu, and Yb; RE = Ce, Pr,and Tb). Cerium is the recombination center and lanthanide codopants act aselectron-trapping centers in GdAlO3:Ce3+,Ln3+.Different lanthanide codopantsgenerate different trap depths. The captured electrons released from thelanthanide recombine at cerium via the conduction band, eventually producingthe broad 5d−4f emission centered at∼360 nm from Ce3+. On the other hand,Sm3+,Eu3+, and Yb3+act as recombination centers, while Ce3+,Pr3+, and Tb3+actas hole-trapping centers in GdAlO3:Ln3+,RE3+. In this situation, wefindevidence that recombination is by means of hole release instead of the morecommonly reported electron release. The trapped holes are released from Pr4+or Tb4+and recombine with the trapped electrons on Sm2+,Eu2+,orYb2+andyield characteristic trivalent emission from Sm3+,Eu3+,orYb3+at∼600,∼617, or∼980 nm, respectively. Lanthanum wasintroduced to engineer the valence band energy and change the trap depth in Gd1−xLaxAlO3:Eu3+,Pr3+andGd1−xLaxAlO3:Eu3+,Tb3+. The results show that the valence band moves upward and the trap depth related to Pr3+or Tb3+decreases.@en

Two different trapping and detrapping processes of chargecarriers have been investigated in GdAlO3:Ce3+,Ln3+(Ln = Pr, Er, Nd, Ho, Dy,Tm, Eu, and Yb) and GdAlO3:Ln3+,RE3+(Ln = Sm, Eu, and Yb; RE = Ce, Pr,and Tb). Cerium is the recombination center and lanthanide codopants act aselectron-trapping centers in GdAlO3:Ce3+,Ln3+.Different lanthanide codopantsgenerate different trap depths. The captured electrons released from thelanthanide recombine at cerium via the conduction band, eventually producingthe broad 5d−4f emission centered at∼360 nm from Ce3+. On the other hand,Sm3+,Eu3+, and Yb3+act as recombination centers, while Ce3+,Pr3+, and Tb3+actas hole-trapping centers in GdAlO3:Ln3+,RE3+. In this situation, wefindevidence that recombination is by means of hole release instead of the morecommonly reported electron release. The trapped holes are released from Pr4+or Tb4+and recombine with the trapped electrons on Sm2+,Eu2+,orYb2+andyield characteristic trivalent emission from Sm3+,Eu3+,orYb3+at∼600,∼617, or∼980 nm, respectively. Lanthanum wasintroduced to engineer the valence band energy and change the trap depth in Gd1−xLaxAlO3:Eu3+,Pr3+andGd1−xLaxAlO3:Eu3+,Tb3+. The results show that the valence band moves upward and the trap depth related to Pr3+or Tb3+decreases.@en