P. Gluchowski

Magnetic studies of GaN nanoceramics doped with 1% of cerium

The magnetization measurements of gallium nitride nanoceramics doped with 1% of cerium and sintered under various pressures were reported. It was found that GaN nanoceramics doped with cerium showed paramagnetic behavior in the wide temperature range. Nanoceramics of GaN with 1% of Ce (as undoped GaN) was diamagnetic one, but under certain temperature the paramagnetic properties started to dominate. This crossover temperature was nonlinearly dependent on the pressure applied during the sintering. The fitting of molar magnetic susceptibility allowed to estimate the Curie temperature, Curie constant and diamagnetic part of susceptibility. As it was found, all the samples showed the antiferromagnetic ordering with θp≈−1 K. Also, the effective magnetic moment was estimated for all of the samples. As a result, magnetic moments in terms of Ce ion were notably larger in comparison with those obtained within the Russell-Saunders coupling model. We suggested that it was the strong influence of amorphous shell which was rising with the pressure applied during the sintering. Finally, we presented dependences of magnetization as a function of applied field. All the samples manifested weak ferromagnetism at high temperatures and paramagnetic behavior in low temperature region.

Up-conversion luminescence of rare earth-doped KGd(WO4)2 phosphors for tunable multicolour light generation

A series of novel KGd(WO4)2 crystalline powders doped with Yb3+/Tm3+, Yb3+/Er3+ and Yb3+/Ho3+ were synthesized using a modified Pechini method. The monoclinic structure of these compounds was confirmed by XRD. The luminescence properties were investigated by measuring up-conversion luminescence spectra and decay curves. KGd(WO4)2 crystalline powders doped with Yb3+/Tm3+, Yb3+/Er3+ and Yb3+/Ho3+ exhibit effective multicolour up-conversion luminescence in the VIS and NIR spectral ranges under 980 nm excitation. The vibrational properties of the materials were investigated using μ-Raman spectroscopy. The assistance of low energy phonons of the KGd(WO4)2 matrix in the energy transfer processes between the excited manifolds of the Yb3+, Er3+, Tm3+ and/or Ho3+ ions during the up-conversion process was discussed. These results indicate that KGd(WO4)2 powders doped with selected Tm3+, Er3+, Ho3+ and Yb3+ ions may be potentially used as single-component multicolour or white emission phosphors.

Bi-functional Bi2ZnOB2O6 single crystals doped with Nd3+ or Pr3+: luminescence and µ-Raman investigations

The investigated Bi2ZnOB2O6 nonlinear optical single crystals doped with Nd3+ or Pr3+ ions were grown by the Kyropoulos method. Bi2ZnOB2O6 single crystals doped with selected RE3+ ions are characterized by high values of nonlinear optical coefficients as well as the effective luminescence of excited RE3+ ions, which make this system a unique candidate for laser converters. The vibrational properties of Bi2ZnOB2O6:Nd3+ and Bi2ZnOB2O6:Pr3+ single crystals were investigated with the use of μ-Raman spectroscopy. The strong emission of Bi2ZnOB2O6:Nd3+ single crystals with maximum at about 1062 nm (4F3/2→4 I11/2 transition) was detected under the excitation at 514 nm. Emission spectrum of Bi2ZnOB2O6:Pr3+ show enhancement of emission with maxima at about 1350 and 1470 nm ( 1D2→3H4 and 1G2→3H5 transition). The effective luminescence of excited Nd3+ or Pr3+ ions in Bi2ZnOB2O6 single crystals as well as excellent nonlinear optical properties of Bi2ZnOB2O6 host suggest that the investigated system can be very useful as a bifunctional crystals for new integrated optical systems such as self-frequency doubling lasers.

Up-conversion luminescence and µ-Raman investigations of KGd(WO 4 ) 2 crystalline powders doped with rare earth ions

KGd(WO₄)₂ /(KGW) micro-crystalline powders, doped with selected rare earth (RE) ions, namely Ho³⁺, Er³⁺, Tm³⁺, Tb³⁺ and/or Yb³⁺ ions, were synthesized using modified Pechini method. RE doped KGW micro-crystalline powders exhibit multicolor up-conversion luminescence in the VIS and NIR spectral ranges under 975 nm laser diode excitation. The spectroscopic properties of KGW:RE³⁺ were investigated using the μ-Raman spectroscopy and optical spectroscopy methods. The investigated KGW:RE³⁺ powders are very promising materials as new generation energy converters with significant potential applications in novel optical devices.