Low-temperature (10 K) photoluminescence excitation and emission spectra of undoped Sr3SiO5 as well as Ce(3+) and Eu(3+) single doped Sr3SiO5 have been investigated. They show the host exciton band and the O(2-) to Eu(3+) charge transfer band at 5.98 eV (207 nm) and 3.87 eV (320 nm) respectively. Low-temperature thermoluminescence measurements are reported for Ce(3+) and lanthanide (Er, Nd, Sm, Dy, Er and Tm) co-doped Sr3AlxSi1-xO5. The results show that Ce(3+) is the recombination centre and Nd, Sm, Dy and Tm work as electron traps with trap depths of 0.95 eV, 1.89 eV, 1.02 eV, and 1.19 eV, respectively. Thermoluminescence excitation spectra of Sr2.98Al0.02Si0.98O5:0.01Ce(3+),0.01Dy(3+) show that the traps can be charged by 260 nm UV excitation.

No abstract

Two series of BaHfO3 powders activated with Eu3+ ions were prepared with a ceramic method. By stoichiometric variations, the dopant was forced to enter either Ba2+ or Hf(IV) sites. X-ray diffraction (XRD) analysis proved that Eu3+ ions preferred substitution of Hf(IV) in BaHfO3, while replacement of Ba2+ encountered difficulties and led finally to separation of a foreign phase, Eu2Hf2O7. Yet, it was shown that the host always incorporated the activator both into Hf(IV) and Ba2+ positions, and the two sites, EuHf ′ and EuBa •, were spectroscopically characterized. From photoluminescence spectra, it appeared that EuBa • gave emissions at 573.6, ∼595, and 626.0 nm, while luminescence from EuHf ′ was practically limited to just one line peaking at 595.6 nm. Luminescence and excitation spectra taken under synchrotron radiation showed that energy from the excited host is preferentially transferred to EuHf ′ compared to EuBa •. At 10K, the latter was not capable of intercepting any energy upon excitation above the fundamental absorption of BaHfO3, which limited the luminescence in such conditions to a single line peaking at 595.6 nm. Also, under excitation with X-rays, practically only the EuHf ′ was able to produce luminescence.

Ca 3 Y 2 Si 3 O 12 powders activated with Eu (0.1−25%) were prepared by means of ceramic method. Their spectroscopic properties in VUV-UV−vis region were investigated. Luminescence measurements indicated that Ca 3 Y 2 Si 3 O 12 prepared in a strongly reducing atmosphere of 20%N 2 −80%H 2 mixture contained both Eu 2+ and Eu 3+ ions, and both were able to generate their characteristic emissions. A superposition of the broad band luminescence of Eu 2+ and narrower 4f → 4f luminescent features of Eu 3+ upon excitation with 395 nm light-emitting diode covered almost the whole visible part of spectrum. The ratio between Eu 2+ and Eu 3+ emissions was reproducible, and, with increasing content of Eu, the relative intensity of the red component from Eu 3+ became systematically stronger. The Eu 2+ luminescence in Ca 3 Y 2 Si 3 O 12 was characterized by an extraordinary large Stokes shift of ∼8960 cm −1 and most probably had an anomalous character with a defect, presumably O-vacancy located in the vicinity of Eu 2+ , being involved in the emission generation. Excitation into the VUV-UV region with synchrotron radiation revealed that at 10 K, despite Eu 3+ and Eu 2+ ions, two kinds of intrinsic emissions, peaking around 340 and 420−440 nm, contributed to the luminescence of Ca 3 Y 2 Si 3 O 12 :Eu. Luminescence measurements in the range of 293−573 K and decay kinetics of Eu 3+ and Eu 2+ emissions revealed that the continuously decreasing fraction of Eu 2+ ions contributed to the emission with increasing temperature, yet the thermal quenching of emission monitored by changes in its decay time could merely be seen above 500 K. The unusual temperature behavior of Eu 2+ luminescence in Ca 3 Y 2 Si 3 O 12 :Eu 2+ ,Eu 3+ was assigned to the instability of exciton-like state diffused over [Eu 2+ -O vac ] defect cluster involved in the luminescence of Eu 2+ . Although the performance of the phosphor was not optimized, 40−44% of the quantum efficiency of the overall luminescence upon near-UV excitation was measured, proving its high potential.

No abstract