Igor Razdobreev

Optical properties of Bismuth-doped silica core photonic crystal fiber

Optical properties of a Bismuth-doped pure silica sol-gel core photonic crystal fiber (PCF) were investigated. We report on the absorption, CW luminescence and time resolved luminescence spectra at different excitation wavelengths at room temperature. Complex structure of the energy levels of Bismuth-connected centers in pure silica glass is put in evidence.

From molecular precursors in solution to microstructured optical fiber: a Sol-gel polymeric route

Solid-core photonic crystal fibers with the core derived from non-doped or Erbium-doped sol-gel silica rods are fabricated. The results demonstrate that the direct polymeric sol-gel route constitutes a promising method to prepare large high quality glass pieces that can be integrated into microstructured optical fibers suitable for passive and active optical fiber applications.

Photoluminescence of sol-gel silica fiber preform doped with Bismuth-containing heterotrinuclear complex

A monolithic Bismuth-Aluminium codoped silica glass was prepared from nano-porous silica xerogels using a conventional solution doping technique with a heterotrinuclear complex and subsequent sintering. This novel approach enabled the preparation of the silica glass which contains a single luminescent center, namely an Al-connected Bi-center.

Optically detected magnetic resonance in bismuth-doped silica glass

The recent discovery of near infrared (NIR) photoluminescence (PL) of bismuth-doped silica glasses [1] led to the development of a new class of laser media that provides broad gain in 1100−1250nm range [2]. However, the luminescent centre (or centres) is not clearly identified up to now and this point is actively discussed in the literature. Different authors tentatively assigned this NIR PL to the electronic transitions of Bi5+ [1], [(AlO4/2)− ,Bi+] complexes, Bi+, Bi2+, clusters of Bi atoms, BiO molecules and, recently, to negatively charged [Bi2]−2 pairs dispersed in glass host [3]. In our recent report we have demonstrated experimentally that at least clusters of Bi atoms should be eliminated from the list of potential candidates [4]. In the present communication we give experimental evidence that the NIR PL observed in bismuth-doped silica glasses should be connected to the electronic transitions from triplet excited states (ES) in contradiction to what was suggested in [3].

Magnetic circular polarization of luminescence in Bismuth-doped silica glass

The magnetic field induced circular polarization of near infrared photoluminescence in Bi-doped pure silica glass was studied in the spectral range of 660 - 1600 nm covering three excited state levels. The highest degree of magnetic circular polarization of luminescence was observed in the lasing, first excited state (peak emission at 1440 nm). The results of variable temperature and variable magnetic field measurements allows to conclude that the near infrared luminescence originates from an isolated non-Kramers doublet of the even-electron system.

On the nature of photoluminescence in Bismuth-doped silica glass

We report on the investigation of Bismuth-doped pure silica glass without other co-dopant by the tech- nique of magnetic circular dichroism (MCD), which allows the direct probing of the ground state of optical centres. Taking into account the results of conventional optical spectroscopy, we show that the observed MCD bands belong to the centre responsible for the red photoluminescence in this material. Measurements of the temperature and field dependences indicate that the MCD effect is caused by the even-electron system. This, however, opposes the widespread opinion that Bi2+ ions are the origin of red photoluminescence in Bismuth-doped silica glasses. On the other hand, the lasing centre responsi- ble for the near infrared photoluminescence does not exhibit any magnetic optical activity connected to its ground state. As a consequence, we conclude that the ground state of lasing centre is a magnetic singlet with the effective spin S = 0.

Photoluminescence in Ga/Bi co-doped silica glass

Bismuth-Gallium co-doped silica glass fiber preform was prepared from nano-porous silica xerogels using a conventional solution doping technique with a heterotrinuclear complex and subsequent sintering. Ga-connected optical Bismuth active center (BAC) was identified as the analogue of Al-connected BAC. Visible and infrared photoluminescence (PL) were investigated in a wide temperature range of 1.46 - 300 K. Based on the results of the continuous wave (CW) and time resolved (TR) spectroscopy we identify the centers emitting in the spectral region of 480 - 820 nm as Bi(+) ions. The near infrared (NIR) PL around 1100 nm consists of two bands. While the first one can be ascribed to the transition in Bi(+) ion, the second band is presumably associated to defects. We put in evidence the energy transfer (ET) between Bi(+) ions and the second NIR emitting center via quadrupole-quadrupole and dipole-quadrupole mechanisms of interactions. Finally, we propose the energy level diagram of Bi(+) ion interacting with this defect.

Anti-Stokes photoluminescence in Ga/Bi co-doped sol-gel silica glass.

Unusual temperature dependence of the anti-Stokes photoluminescence (ASPL) at 734 nm was found in Ga/Bi co-doped sol-gel silica glass. While in the temperature range of 450-873 K, the behavior of ASPL is completely determined by the thermal population of the excited state levels, its intensity is continuously increasing with decreasing temperature in the range of 77-430 K. By measuring the pump power dependence of ASPL at 300 K, we show that the latter can be described via the two-step intracenter excitation process and subsequent relaxation. Based on the measurements of temperature dependence of the excitation spectra of near infrared band (at 1140 nm) and that corresponding to the ASPL (at 734 nm), we propose a simple rate equation model to explain the unusual behavior of ASPL.