1. Experimental results II Experimental results I
Influence of halides on the luminescence of silver molecular clusters in photo-thermo-refractive glasses.
V.D. Dubrovin, A.I. Ignatiev, N.V. Nikonorov, A.I. Sidorov
ITMO National Research University, Kronverkskii 49, St.Petersburg, Russia
Introduction
Experimental
Luminescence glasses with neutral molecular clusters of silver are perspective for use as spectral con-verters radiation in solar energy and LED white light. Photo-thermo-refractive (PTR) glass other than the above applications, may be used for the optical recording and storage of information by allowing the local transformation of charged molecular clusters in neutral by UV irradiation. The aim of this work was to investigate the effect of NaCl and NaBr concentration on the spectral characteristics of silver’s molecular clusters luminescence in PTR glasses.
In present work we synthesized the PTR glasses of Na2O-ZnO-Al2O3-SiO2 system, with variable halides halogens (F, Br, Cl) and their concentrations. The glasses were doped with photo-sensitive dopant of CeO2 (0.007 mol.%), reductant do-pant of Sb2O3 (0.04 mol.%) and also Ag2O. The Ag2O content was taken, for the PTR(Cl) and PTR(Br) group samples, to be equal to 0.13 and mol.% respectively. The glasses were synthesized in SPb National Research University ITMO. The synthesis was performed at 1450 OC. Tg = 494 OC was measured with the use of DSC STA6000 (Perkin-Elmer). Luminescence spectra were measured by spectrometer EPP2000-UVN-SR (StellarNet) with excitation by semiconductor laser with  = 405 nm.
Experimental results II
Experimental results I
Photos of the samples (PTR-Cl) and their luminescence (exc = 365 nm).
1 – initial glass with charged MC Agn.
2 – after UV irradiation with neutral MC Agn.
3 – after UV irradiation and TT with temperature less, than Tg.
4 – after UV irradiation and TT with temperature more, than Tg.
The corresponding absorption spectra are below:
Luminescence spectra after UV irradiation (exc = 405 nm).
After UV
530 nm
NaCl content (mol %):
NaBr
NaCl
(1) 0, (2) 0.52, (3) 0.74, (4) 1.0, (5) 1.5, (6) 2.0.
NaBr
NaCl
544 nm
NaBr content (mol %):
After UV and TT (T=400 OC)
(1) 0, (2) 0.25, (3) 0.66, (4) 1.0, (5) 1.5.
After UV and TT (C=1.5 mol.%)
NaBr
NaCl
Thermal treatment at T > Tg:
In the case of F agent only Ag nanoparticles are grown in the PTR glass host and it has a small (10 cm-1) absorption coefficient at plasmon band (max = 424 nm). In the case of F and Br agents we observed by XRD the growth of two crystalline phases: mixed crystals NaBr-AgBr on the Ag nanoparticles surface and NaF crystals on it. In this case a red wavelength shift of the peak plasmon resonance up to 70 nm was observed. The achieved absorption coefficient was 50 cm-1. In the case of fluoride and chloride agents we observed the growth of some crystalline phases NaCl-AgCl on the silver nanoparticles and a red wavelength shift of the peak plasmon resonance up to 30 nm. The absorption coefficient achieved in this case was 200 cm-1.
UV and TT at T<Tg result in the appearance of the intense luminescence in spectral range nm under excitation λ = 405 nm. The increase of NaCl(Br) concentration in the PTR glass result in the increase of luminescence intensity. This allows to make a conclusion, that the part of Ag MC exist in glass in a form of complex Agn-Cl(Br). The TT of the glasses at OC led to 2.5 times increase of luminescence intensity.
An example of calculated structures of the stable MC Agn-Cl (n = 2-5)
J. Chem. Phys (2005)
Summary
The research has shown that:
1. UV radiation of PTR glass results in a formation of neutral SMCs, that have an absorption band within of nm and a luminescence band in wide visible range of nm;
2. The presence of NaCl and NaBr in PTR glass contribute to the formation and growth of silver nanoparticles. The growth of nanoparticles is accompanied by the formation crystal halide shell on a silver core.
3. The increase of halides (NaCl, NaBr) concentration in PTR glass and TT at T < Tg led to the increase of silver MC luminescence intensity.
4. The spectral shift of luminescence maximum when NaCl is replaced by NaBr indicates the formation of Agn-Cl(Br) complexes.