Luminescence Properties of Tb-Doped Yttrium Disilicate Prepared by the Sol–Gel Method

A sol–gel method for the synthesis of nanosized powders of yttrium disilicate doped with Tb^{3 +} is presented. The influence of grain size and annealing temperature on the structure and luminescence properties of the materials obtained has been investigated. The preparation of glass-ceramic composite has been also described. The effect of incorporating the nanocrystals into sol–gel silica glasses on their physicochemical properties has been shown and discussed. A lack of influence of the annealing above 1300°C on the lifetimes measured for the nanocrystals embedded in the glass, as compared to the Y₂Si₂O₇:Tb^{3 +} powders, has been observed.     

Laser-induced time-resolved luminescence of natural sillimanite Al2SiO5 and synthetic Al2SiO5 activated by chromium

Luminescence of natural sillimanite Al₂SiO₅ was studied by a laser-induced time-resolved technique combined with absorption spectroscopy. It was found that two red broad emission bands are connected to Fe³⁺ and Cr³⁺ luminescence centers. Chromium participation in luminescence was proved by the study of synthetic sillimanite activated by Cr. Several narrow emission lines have been found which were preliminary ascribed to Mn⁴⁺ and V²⁺ luminescence centers.     

Optically stimulated heating using Nd3+ doped NaYF4 colloidal near infrared nanophosphors

Although efficient in heat generation, gold nanoparticles dedicated for photostimulated localized hyperthermia treatment (LHT) lack luminescent properties suitable for detection in heterogeneous and autofluorescent tissue. Here, we study and report the use of bifunctional luminescent neodymium (Nd³⁺) ions doped ??-NaYF₄ colloidal nanoparticles as potential nanoheaters suitable for LHT. Up to 35°C (0.8°C/mW@514.5?nm) temperature rise in ??0.5?ml colloidal 25%Nd³⁺:NaYF₄ solution was achieved in comparison to around a 4°C rise for the undoped colloidal NaYF₄. The maximum temperature (T _max?) was linearly proportional to the concentration of Nd³⁺ dopant. The time required to elevate temperature to 1/e×T _max? varied from 100 to 135 seconds. The proposed approach gives premises to the construction of multi-functional therapeutic agents detectable by means of fluorescence molecular imaging.     

Solvent effect on intensities of hypersensitive bands of lanthanide perchlorates

The measurements of oscillator strengths of hypersensitive bands for Ln(ClO₄)₃ (Ln  Nd, Ho, Er) in different solvents are reported. The sesults are discussed within the framework of the polarizability mechanism.     

Magnetic-field-induced radiationless transitions

A quantum-mechanical theory of the magnetic field effect on radiationless transitions in an isolated molecule is presented. The mechanism of this phenomenon is a second-order process relying on the simultaneous radiationless relaxation of an excited electronic state and the interaction of the molecule with a constant uniform magnetic field.     

Influence of terbium on structure and luminescence of nanocrystalline TiO2 thin films

In this work analysis of the structural and optical properties of TiO₂ thin films doped with terbium has been described. Samples were prepared by a high energy reactive magnetron sputtering process under low pressure of oxygen plasma. X-ray diffraction results have shown that different TiO₂ crystal forms have been produced, depending on the amount of Tb dopant. The undoped matrix had rutile structure with crystallites with a size of 8.7 nm, while incorporation of 0.4 at. % of Tb into the film during the sputtering process resulted in anatase structure with bigger crystallites (11.7 nm). Increasing the amount of terbium up to 2 at. % and 2.6 at. % gave rutile structure with crystallites with a size of 6.6 nm for both films. However, Raman spectroscopy has revealed that in the case of TiO₂:(2 at. % Tb), except for the rutile form, the presence of fine-crystalline anatase was observed. Moreover, the lack of Raman peaks shift attests to the lack of stress in the titania lattice of all of the TiO₂:Tb films. This fact indicates localization of Tb3+ ions on the surface of TiO₂ nanocrystals. In the case of optical investigation, results have shown that doping with terbium has a significant influence on the properties of TiO₂, but it does not decrease the high transparency of the matrix. The observed changes of the transmission characteristics were produced only due to modification of the TiO₂:Tb structure. Photoluminescence measurements have shown that emission of light from TiO₂:Tb films occurs when the amount of terbium is 2.6 at. %. Based on the obtained results a scheme of direct energy transfer from titanium dioxide matrix (with rutile structure) to Tb³⁺ ions has been proposed.     

Optical Behavior of ZnS:Cu Microcrystals Embedded in Porous Silica Gels

Emission and excitation spectra of ZnS:Cu microcrystals trapped in porous silica xerogels are presented. This system is characterized by intense, long-lived green emission at room temperature. It was observed that this emission was greatly reduced after compressing the xerogel samples.     

Spectroscopic properties of Yb3+-doped Y3Al5O12 nano-ceramics obtained under different sintering pressures

Yb³⁺:YAG nano-ceramics have been obtained by a low temperature/high pressure sintering process. Structural properties have been studied by X-ray diffraction (XRD). Grain sizes and R.M.S micro-strains have been calculated based on the XRD patterns by Rietveld analysis method. Emission spectra and decay curves have been recorded and analyzed. It has been observed that the decay time decreases with the increase of sintering pressure. Presence of Yb³⁺–Yb³⁺ pairs have been detected by cooperative emission spectroscopy.     

Optical investigation of the emission lines for Eu and Tb ions in the GaN powder host

Gallium nitride (GaN) doped by Eu³⁺ and Tb³⁺ ions have been synthesized using powder technology. The emission and absorption spectra have been obtained by using photoluminesence technique and correlated with the local structural environments. The room temperature yellow emission from GaN grains as well as from Eu³⁺ and Tb³⁺ ions has been observed for nano- as well as for microGaN grains. Additionally, for GaN:1%Eu³ micrograins the blue emission from GaN nanocrystals has been observed.     

Cathodoluminescence of Lu 2 O 3 :Tb

Spectroscopic properties of Lu 2 O 3 :Tb pellets sintered at 1000 v C or 1700 v C were investigated. The sintering temperature did not influence the optically excited emission and excitation spectra of the materials. However, the treatment temperature did influence the emission under cathode-rays stimulation. While the specimens sintered at 1000 v C showed only luminescent lines above 480 v nm resulting from a radiative relaxation of the 5 D 4 level, the samples heated at 1700 v C did show some luminescence in the blue region resulting from 5 D 3 M 7 F J emission. The blue emission could be recorded exclusively upon cathode-rays irradiation.