Tunable luminescence from Ce-doped aluminoborosilicate glasses

International audienceA series of aluminoborosilicate glasses were prepared using the melt-quenching technique for mixture of stoichiometric amounts of SiO 2 , Al 2 O 3 , H 3 BO 3 , Na 2 CO 3 , and ZrO 2 with adding of different amounts of CeO 2. The samples were investigated by means of luminescence spectroscopy. Tunable luminescence from violet to blue/green was observed from these glasses with different Xe-lamp excitation wavelengths ranging from 370 to 480 nm as well as with laser excitation of 266 and 355 nm. Moreover it was found that the possibility of tuning the light by changing of excitation wavelength was not unique. The same effect was observed by adjusting conditions for luminescence measurements as well as under exposure to β-irradiation. The obtained phenomena could be explained taking into account structural characteristics of this glass and it could be concluded that tunable luminescence results from the presence of different Ce-sites the glass matrix. Thus the results suggest that Ce-doped glasses could be considered as conversion materials for blue light-emitting diode chips to generate white light-emitting diodes. Ce 3+ ions were widely used as activators in various fluoride and oxide materials. The preparation of RE-doped phosphor materials for application in advanced illumination technologies has been the subject of intense research during recent decades. These researches are stimulated by the necessity of increasing the efficiency in white light emitting solid state devices which represent an alternate lightning source [1

Effect of Sm-, Gd- codoping on structural modifications in aluminoborosilicate glasses under beta-irradiation

Two series of Sm-, Gd-codoped aluminoborosilicate glasses with different total rare earth content have been studied in order to examine the codoping effect on the structural modifications of beta-irradiated glasses. The data obtained by Electron Paramagnetic Resonance spectroscopy indicated that relative amount of Gd3+ ions located in network former position reveals non-linear dependence on Sm/Gd ratio. Besides, codoping leads to the evolution of the EPR signal attributed to defects created by irradiation: superhyperfine structure of boron oxygen hole centres EPR line becomes less noticeable and resolved with increase of Gd amount. This fact manifests that Gd3+ ions are mainly diluted in vicinity of the boron network. By Raman spectroscopy, we showed that the structural changes induced by the irradiation also reveal non-linear behaviour with Sm/Gd ratio. In fact, the shift of the Si-O-Si bending vibration modes has a clear minimum for the samples containing equal amount of Sm and Gd (50:50) in both series of the investigated glasses. In contrast, for single doped glass there is no influence of dopant's content on Si-O-Si shift (in case of Gd) or its diminution (in case of Sm) occurs which is explained by the reduction process influence. At the same time, no noticeable effect of codoping on Sm3+ intensity as well as on Sm2+ emission or on Sm reduction process was observed

Irradiation effects in oxide glasses doped with transition and rare-earth elements

International audienceThe effect of -irradiation on silicate and aluminoborosilicate glasses doped with transition metals (TM) and rare earth (RE) elements has been studied using Electron Paramagnetic Resonance (EPR), Raman and luminescence spectroscopy. Irradiation leads to the reduction of both Cr and Mn ions in both types of glass matrix. It is shown that even small amounts of TM dopants completely block defect production, as occurs under irradiation in non-doped glasses. As well, TM doping results in the disappearance of structural changes in the glass (densification, polymerization increase and Na migration) for doses of ~ 10 Gy. Unlike TM-doped matrices, incorporation of RE ions into aluminoborosilicate glass blocks neither defect production nor structural changes in glass matrices during irradiation. Simultaneously, we observe a reduction of RE ions, most clearly demonstrated for Ce ions in aluminoborosilicate glasses. We propose that the relative stability of the different charge states of the RE ions is linked to the efficiency of the reduction process, and therefore to the evolution of the glass structure during irradiation

Optical properties and valence state of Sm ions in aluminoborosilicate glass under β-irradiation

International audienceSm-doped borosilicate glasses exposed to β-irradiation with doses from 8 × 105 up to 4 × 109 Gy have been studied by luminescence, Raman and electron paramagnetic resonance (EPR) spectroscopies. The luminescence spectra for pristine and irradiated glasses reveal that the β-irradiation process affects valence state of samarium ions. Intense emission at 684 and 727 nm excited by Ar+ laser (514.5 nm) due to the transition of Sm2+ ion was observed after irradiation. Relative proportion of Sm2+ ions estimated as a function of both Sm2O3 content and irradiation dose has the tendency to increase with increasing irradiation dose. In contrast, the EPR spectra of the studied samples reveal a decrease of the defect content, which are mostly hole defects, produced during irradiation, as a function of Sm2O3 content. Finally, the addition of Sm2O3 leads to a decrease of the Si–O–Si bending vibration modes shift and polymerisation changes under irradiatio

Oxidation of Sm2+ in beta-irradiated Sm-doped borosilicate glasses under laser illumination

Borosilicate glasses doped with samarium have been prepared. Samples exposed to 4 x 10(9) Gy of beta-irradiation have been investigated by fluorescence measurements, showing a strong reduction process of SM3+ to SM2+ ions in the irradiated samples. Oxidation of Sm2+ was observed in this glass as a result of frequency-doubled cw Nd:YAG laser irradiation, but not when using a pulsed titanium-doped sapphire laser. Influence of laser intensity was studied, showing that an increase of the laser intensity could induce complete oxidation of SM2+ ions. Such effect is not observed at low temperature nor using ultra short laser pulses. The conclusion is that the effect is of thermal origi