Broadband Near-infrared Luminescence And Optical Amplification In Cr⁴⁺-doped Transparent Glass Ceramics

With the speedy development of computer network and telecommunicationtechnology, super-high-capacity information transmission and super-high-speed signalprocessing technologies are demanded. Recently, great progress has been achieved inthe OH^- elimination of silica fibers, and as a result, the telecommunicationtransmission has been extended to the range from 1.2 to 1.7 urn. However, theconventional rare-earth-doped fiber amplifiers only work on certain bands because ofnature charcteristics of f-f electronic transitions from rare-earth ions. Narrowwavelength regions can be used as gain region by rare-earth-doped fiber amplifiers,such as C (1530-1565 nm), L (1570-1605 nm), and S (1450-1520 nm) bands byerbium-doped fiber amplifiers. The narrow gain region sets limitation for the numbersof signal channel, which makes serious trouble for super-high-capacity informationtransmission. If optical amplification can be realized in a broader band even in thewhole telecommunication window by one optical fiber, signal transmission rate can beenhanced substantially, and great revolution of telecommunication technology can bebrought out.This thesis provides a comprehensive review on the luminescence characteristicsof rare-earth, transition-metal and main-group ions doped materials, gives anoverview of the recent progress and problems, and puts forwards their future researchdirections. Based on that review, several typical and important characteristics areaddressed to develop novel light source, such as high efficience, long luminescencelifetime, temperature-dependence, and superbroadband. Some new research ideas ondesign and construction of materials are presented, and some novel broadbandnear-infrared luminescent materials are developed. Thermal analysis (DTA), X-raydiffraction (XRD), transmission electronic microscope (TEM), absorption spectra, andphotoluminescence spectroscopy (PL) were used to study the structure andluminescence properties of the materials. A series of important conclusions andinnovative results with practical significance were obtained.Transparent glass ceramics containing Cr⁴⁺-doped Li₂ZnSiO₄ nano-crystallites are prepared. The glass ceramics show intense broadband near-infrared luminescence(centerd at 1210 nm) and long luminescence lifetime (90μs) at room temperature.The super long luminescence lifetime and high quantum efficiency of the presentglass ceramics are contributed by active center Cr⁴⁺ incorporated at specific distortedtetrahedron. In the given tetrahedral crystal field, the lowest sub-level of ³T₂(³F) ismixed with the top sub-level of ¹E, and electronic transition between the mixed leveland ground state produces the long broadband near-infrared luminescence. Opticalgain can be realized by Cr⁴⁺-doped Li₂ZnSiO₄ glass ceramics at room temperature dueto advanced ceraming process and high efficiency of Cr⁴⁺ in Li₂ZnSiO₄ crystals. Insingle-pass two-wave-mixing configuration, optical gain efficiency of 1.27 cm^-1 isobtained pumped by an 808 nm laser diode with 0.80 W pumping source.Transparent glass ceramics containing Cr⁴⁺-doped Li₂MgSiO₄ nano-crystallitesare prepared, and their spectral and luminescent properties are examined. As the sameas Cr⁴⁺-doped Li₂ZnSiO₄ glass ceramics, Cr⁴⁺-doped Li₂MgSiO₄ glass ceramics showluminescence lifetime more than ten times longer than other kinds of glass ceramics,which is also attributed by the electronic transition between specific mixed level andground state. The spectral and luminescent characteristics of the glass ceramics showobvious temperature-dependence. As the environment temperature increases, theemission intensity decreases, the emission band shifts blue-ward, and the full width athalf maxium of the luminescence is enlarged. These phenomena are related withnon-radiative transitions originated by photon-phonon interactions.Transparent glass ceramics containing Cr-Ni-codoped Mg₂SiO₄ nano-crystallitesare prepared, and their spectral and luminescent properties are examined. The resultsshow three broad emission bands centered at 950, 1150, and 1500 nm are originedfrom different kinds of transition-metal ions Cr³⁺, Cr⁴⁺, and Ni²⁺, respectively. Thesebroad emission bands overlap together and superbroadband near-infraredluminescence with full width at half mixium of 700 nm is observed. Thesuperbroadband emission can cover the full telecommunication window. However,energy transfer from Cr³⁺ and Cr⁴⁺ to Ni²⁺, as well as low quantum efficiency of Ni²⁺in Mg₂SiO₄ crystals makes the total luminescence efficiency too low.