Spectroscopy and Thermoluminescence of LuAlO3:Ce

The present status of the LuAlO3:Ce scintillator is reviewed. Scintillation mechanism of this material is based on capture by Ce3+ of holes and then electrons from their respective bands. Results of spectroscopic and thermoluminescence experiments are presented to support this model

Statin treatment increases lipoprotein(a) levels in subjects with low molecular weight apolipoprotein(a) phenotype

Background and aims: We aimed to evaluate the effect of statin treatment initiation on lipoprotein(a) [Lp(a)] levels in patients with dyslipidemia, and the interactions with the apolipoprotein(a) [apo(a)] phenotype, LPA single nucleotide polymorphisms (SNPs) and change in LDL cholesterol. Methods: The study population consisted of patients with dyslipidemia, predominantly familial hypercholesterolemia, who first initiated statin treatment (initiation group; n = 39) or were already on stable statin treatment for at least 4 months (control group; n = 42). Plasma Lp(a) levels were determined with a particle-enhanced immunoturbidimetric assay before and at least 2 months after start of statin treatment in individuals of the initiation group, and at two time points with an interval of at least 2 months in the control group. High and low molecular weight (HMW and LMW, respectively) apo(a) phenotype was determined by immunoblotting, and the common LPA SNPs rs10455872, rs3798220 and rs41272110 by Taqman assay. Results: Plasma Lp(a) levels did not increase significantly in the initiation group (median 20.5 (IQR 10.9–80.7) to 23.3 (10.8–71.8) mg/dL; p = 0.09) nor in the control group (30.9 (IQR 9.2–147.0) to 31.7 (IQR 10.9–164.0) mg/dL; p = 0.61). In patients with the LMW apo(a) phenotype, Lp(a) levels increased significantly from 66.4 (IQR 23.5–148.3) to 97.4 (IQR 24.9–160.4) mg/dL (p = 0.026) in the initiation group, but not in the control group and not in patients characterized by the HMW apo(a) phenotype. Interactions with common LPA SNPs and change in LDL cholesterol were not significant. Conclusions: Statins affect Lp(a) levels differently in patients with dyslipidemia depending on the apo(a) phenotype. Statins increase Lp(a) levels exclusively in patients with the LMW apo(a) phenotype

Thermoluminescence as a Research Tool to Investigate Luminescence Mechanisms

Thermally stimulated luminescence (TSL) is known as a technique used in radiation dosimetry and dating. However, since the luminescence is very sensitive to the defects in a solid, it can also be used in material research. In this review, it is shown how TSL can be used as a research tool to investigate luminescent characteristics and underlying luminescent mechanisms. First, some basic characteristics and a theoretical background of the phenomenon are given. Next, methods and difficulties in extracting trapping parameters are addressed. Then, the instrumentation needed to measure the luminescence, both as a function of temperature and wavelength, is described. Finally, a series of very diverse examples is given to illustrate how TSL has been used in the determination of energy levels of defects, in the research of persistent luminescence phosphors, and in phenomena like band gap engineering, tunnelling, photosynthesis, and thermal quenching. It is concluded that in the field of luminescence spectroscopy, thermally stimulated luminescence has proven to be an experimental technique with unique properties to study defects in solids

On the separation of quartz OSL signal components using different stimulation modes

We investigate both theoretically and experimentally the effect of stimulation mode on the separation of quartz optically stimulated luminescence (OSL) components. We find that, when assuming first-order kinetics with the detrapping probability proportional to stimulation intensity, the OSL signal is a function of the cumulative stimulation energy and not affected by the stimulation mode. This is confirmed by close correspondence between continuous wave (CW), linearly modulated (LM) and hyperbolically modulated (HM) OSL data for some of the samples studied. For other samples the data obtained using LM stimulation differ from that obtained using the other stimulation modes. This may be due to a contribution to the OSL signal from feldspars, or it may indicate that the behaviour of these samples is not adequately described by first-order kinetics. We suggest that CW stimulation is the method of choice for dating purposes as it allows the fastest readout with the greatest signal-to-noise ratio, and because it has a constant background. HM stimulation provides a good alternative when higher resolution is needed for the initial part of the shine-down curve

Insight into the Thermal Quenching Mechanism for Y₃Al₅O₁₂:Ce³⁺ through Thermoluminescence Excitation Spectroscopy

Y₃Al₅O₁₂(YAG):Ce³⁺ is the most widely applied phosphor in white LEDs (w-LEDs) because of strong blue absorption and efficient yellow luminescence combined with a high stability and thermal quenching temperature, required for the extreme operating conditions in high-power w-LEDs. The high luminescence quenching temperature (∼600 K) has been well established, but surprisingly, the mechanism for temperature quenching has not been elucidated yet. In this report we investigate the possibility of thermal ionization as a cause of this quenching process by measuring thermoluminescence (TL) excitation spectra at various temperatures. In the TL excitation (TLE) spectrum at room temperature there is no Ce³⁺:5d₁ band (the lowest excited 5d level). However, in the TLE spectrum at 573 K, which corresponds to the onset temperature of luminescence quenching, a TLE band due to the Ce³⁺:5d₁ excitation was observed at around 450 nm. On the basis of our observations we conclude that the luminescence quenching of YAG:Ce³⁺ at high temperatures is caused by the thermal ionization and not by the thermally activated cross over to the 4f ground state. The conclusion is confirmed by analysis of the positions of the 5d states of Ce³⁺ relative to the conduction band in the energy band diagram of YAG:Ce³⁺

Controlled Electron–Hole Trapping and Detrapping Process in GdAlO₃ by Valence Band Engineering

Two different trapping and detrapping processes of charge carriers 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 as electron-trapping centers in GdAlO₃:Ce³⁺,Ln³⁺. Different lanthanide codopants generate different trap depths. The captured electrons released from the lanthanide recombine at cerium via the conduction band, eventually producing the 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⁺ act as hole-trapping centers in GdAlO₃: Ln³⁺,RE³⁺. In this situation, we find evidence that recombination is by means of hole release instead of the more commonly reported electron release. The trapped holes are released from Pr⁴⁺ or Tb⁴⁺ and recombine with the trapped electrons on Sm²⁺, Eu²⁺, or Yb²⁺ and yield characteristic trivalent emission from Sm³⁺, Eu³⁺, or Yb³⁺ at ∼600, ∼617, or ∼980 nm, respectively. Lanthanum was introduced to engineer the valence band energy and change the trap depth in Gd_1–<i>x</i>La_<i>x</i>AlO₃:Eu³⁺,Pr³⁺ and Gd_1–<i>x</i>La_<i>x</i>AlO₃:Eu³⁺,Tb³⁺. The results show that the valence band moves upward and the trap depth related to Pr³⁺ or Tb³⁺ decreases