No abstract

We report results of the luminescence properties of the three garnet type phosphors Ce3+-doped Ca3Sc2Si3O12 (CSSO:Ce3+), Sr3Y2Ge3O12 (SYG:Ce3+) and Y3Al5O12 (YAG:Ce3+), investigated using optical spectroscopy techniques and vacuum referred binding energy (VRBE) diagram analysis.

The luminescence spectroscopy of Tb 3+ and Eu 3+ has been studied in the Ca 9 Tb(PO 4 ) 7 , Ca 9 Eu(PO 4 ) 7 , and Ca 9 Tb 0.9 Eu 0.1 (PO 4 ) 7 materials having a whitlockite structure, by using excitation in the near UV, vacuum UV and X-ray regions. The Eu 3+ ion in Ca 9 Eu(PO 4 ) 7 is located mainly in two cationic sites, as evidenced by the fine structure of the 5 D 0 → 7 F 0 transition at 5 K. In the case of Ca 9 Tb 0.9 Eu 0.1 (PO 4 ) 7 , weak Tb 3+ → Eu 3+ energy transfer is observed upon excitation in the UV bands of Tb 3+ . The low efficiency of the transfer appears to be due to slow energy migration in the 5 D 4 subset of the Tb 3+ ions. The overall behavior is strongly affected by the multisite and disordered nature of the Tb-based whitlockite host.

No abstract

The influence of the Ce3+ concentration on the excitation and emission characteristics, thermal stability, and charge-trapping–detrapping dynamics, of the green-emitting phosphor Ce3+ doped calcium scandium oxide (CaSc2O4) with very dilute Ce3+ substitutions (0.5, 1.0, and 1.5%), has been investigated using optical spectroscopy techniques. The diffuse reflectance and excitation spectra are found to exhibit a nonsystematic behavior with varying Ce3+ concentration, mainly linked to spectral band-overlap, whereas the emission spectra display only minor changes with varying Ce3+ concentration, suggesting that the local structural coordination of the Ce3+ dopants remains the same for different Ce3+ dopant levels. The major impact of Ce3+ concentration is seen on the thermal quenching temperature, which is found to be as high as T 50% ≈ 600 K for the most dilute Ce3+ doping (0.5%), followed by T 50% ≈ 530 K for 1.0% doping and T 50% ≈ 500 K for 1.5% doping, respectively. The materials are found to display a red-shift of the emitted light from 518 to 535 nm with increasing temperature from T = 80 K to T = 800 K, for all Ce3+ dopant levels. Thermoluminescence glow curves provide evidence for five charge-trapping defects, which are found to exhibit different charge-trapping dynamics for excitation into different 5d levels. It is argued that the three deeper traps can be filled by athermal tunneling of charges from the Ce3+ 5d 1 level, while the two shallower traps can only be filled when the charges move through the conduction band of the material.

Ferroelectric patterning is often used in advanced photonics and optoelectronic devices to increase their operational bandwidth and functionality, providing novel and unique performances. However, the extension of the ferroelectric structures to two‐dimensional geometries is currently limited to very few oxides and phosphates systems, which constrains its current and future applications. Here, careful processing based on e‐beam lithography and poling is employed to fabricate the first example of a two‐dimensional nonlinear photonic crystal in Barium Magnesium Fluoride, BaMgF4, a ferroelectric fluoride crystal with an extraordinary transparency ranging from the deep ultraviolet (≈126 nm) to the mid infrared (≈13 μm). The optical characterization shows the possibility of obtaining simultaneously up to three different Cerenkov‐type second harmonic generation processes distributed in a conical geometry via χ(2)‐quasi‐phase‐matching technique. Additionally, the remarkably high χ(3) nonlinear response of BaMgF4 crystal in the UV spectral region is exploited to demonstrate what is believed to be the highest direct UV‐third harmonic generation conversion efficiency in a solid state system via pure χ(3) nonlinear process. Together, the results highlight the outstanding opportunities offered by nonlinear photonic structures as innovative avenues to manipulate the light generation and control with reliable multifunctional optical character.

No abstract

Eu 3+ (1 mol %)-doped Ca 2 LnSbO 6 (replacing Ln 3+ ; Ln = Lu, Y, Gd, and La) and Ca 2 EuSbO 6 were synthesized and structurally characterized by means of X-ray powder diffraction. The Eu 3+ luminescence spectroscopy of the doped samples and of Ca 2 EuSbO 6 has been carefully investigated upon collection of the excitation/emission spectra and luminescence decay curves of the main excited states. Surprisingly, apart from the dominant red emission from 5 D 0 , all the doped samples show an uncommon blue and green emission contribution from 5 D J ( J = 1, 2, and 3). This is made possible thanks to both multiphonon and cross-relaxation mechanism inefficiencies. However, the emission from 5 D 3 is more efficient and the decay kinetics of the 5 D J ( J = 0, 1, and 2) levels is slower in the case of Y- and Lu-based doped samples. This evidence can find a possible explanation in the crystal chemistry of this family of double perovskites: our structural investigation suggests an uneven distribution of the Eu 3+ dopant ions in Ca 2 YSbO 6 and Ca 2 LuSbO 6 hosts of the general A 2 BB′O 6 formula. The luminescent center is mainly located in the A crystal site, and on average, the Eu–Eu distances are longer than in the case of the Gd- and La-based matrix. These longer distances can further reduce the efficiency of the cross-relaxation mechanism and, consequently, the radiative transitions are more efficient. The slower depopulation of Eu 3+ 5 D 2 and 5 D 1 levels in Ca 2 YSbO 6 and Ca 2 LuSbO 6 hosts is reflected in the longer rise observed in the 5 D 1 and 5 D 0 decay curves, respectively. Finally, in Ca 2 EuSbO 6 , the high Eu 3+ concentration gives rise to an efficient cross-relaxation within the subset of the lanthanide ions so that no emission from 5 D J ( J = 1, 2, and 3) is possible and the 5 D 0 decay kinetics is faster than for the doped samples.