Preparation And Investigation Of Near-infrared Luminescence Properties Of Organic-inorganic Hybrid Materials For Optical Amplifiers

In this thesis, Synthesis, characterization and photophysical properties of neodymium and erbium complexes have been described with the aim to incorporate into organic-inorganic hybrid materials for applications such as optical waveguide amplifiers operating at the wavelengths of standard telecommunication windows. Toward this aim, firstly the matrix for this purpose should be investigated; Secondly near-infrared (NIR) photoluminsecen properties of lanthanide ions should be understood and novel pathways for the enhancement of near-infrared photoluminsecence properties should be explored further.In Chapter 2, the recent literature concerned with NIR photoluminsecent lanthanide ions in different waveguide matrixes has been described. Then, the remarkable issue is non-radiative deactivation of excited states of Ln³⁺ by the impurity. This quenching renders that Ln³⁺ emittes rather inefficiently in organic-inorganic hybrid matrix. Furthermore, a number of basic properties of NIR emitting ions have been treated with the emphasis on organic lanthanide chelates for doping. The final part of Chapter 2 has been devoted to more general sensitization pathways for NIR emission of lanthanide ions: a) NIR emission with sensitizer of organic ligands; b) NIR emission with sensitizer of visible organic dyes; c) NIR emission with sensitizer of other lanthanide ions.Firstly in Chapter 3 various prescursor derived organically modified silicates by multi-step sol-gel process have been studied for their optical loss in NIR region. With VTES-derived as the appropriate matrix, the effect of sol-gel parameters on the optical loss has been investigated. And VTES-derived and MTES-derived materials modified with TPOZ are suitable for guiding layer and coating layer respectively considering their index refractive.Secondly In Chapter 4 and 5, neodymium and erbium complexes have been studied for NIR luminescence properties, and additive ligand TPPO or Phen can enhance them. Fluoridation of β-diketones can enhance the properties of ternary erbium complexes but affect other complexes' properties irregularly. DBM and TTA derived complexes behave better than other complexes correspondly, with Nd(TTA)₃(TPPO)₂, Er(TTA)₃(TPPO)₂ and ErQ₃ to be execellent ones among all investigated complexes. Judd-Ofelt theory hasbeen applied on the analysis of luminescent properties on the purpose of the selection of the best dopant. Moveover, Judd-Ofelt parameters have been correlated with the ligands. Also erbium metal-organic frameworks with linkers BDC and flurorided BDC-F4 are inspired to obtained novel species with low quenching impurity themselves.Thirdly in Chapter 4 and 5, Nd(TTA)₃(TPPO)₂ is incoperated into VTES gel film. The effect of excitation source, doping concentration and heat-treatment temperature on luminesce properties has been discussed. The best doping concentrion for avoiding concentration quenching is 6.02x10²⁰ ions/cm³. Er(HFA)₃(TPPO)₂ doped film is characterized, too. In order to incorperate low-soluble ErQ₃ or NdQ₃ into gel film, A in-situ synthesis tenchnique is employed.Finally, novel pathways to enhance near-infrared photoluminsecence properties are explored further.In Chapter 4 and 5, Organic ligand acting as an antenna is a well-known strategy in order to enhance visible luminescence from Eu³⁺ and Tb³⁺. Here as for NIR luminescence organic ligands as sensitizers have taken HFA and Q as examples with their energy transferring to erbium ion investigated.In Chapter 6 a novel bi-metallic complex with erbium and yetterbium is proposed with a purpose to realize the sensitization of Er³⁺ by Yb³⁺ in the same complex. The crystallology investigation and TG-DSC result indicate that bi-metallic complex Er_1/2Yb_1/2(HFA)₃(TPPO)₂ possesses the same structure with monometallic complexes Er(HFA)₃(TPPO)₂ and Yb(HFA)₃(TPPO)₂. The energy-transfer mechanism has been proved as Forster-type dipolar-dipolar interaction mechanism, which happens on excitation at 355 nm and 980 nm. Accordingly the energy transfer rates between yetterbium and erbium are calculated.It is well-known that organic chromophores or dyes generally possess more than 3-order magnitude larger absorption cross-section than lanthanide ions so that it is possible to indectly excite Ln³⁺ by dyes effectively. However the recent methods to approach this always are involved sophisticated organic synthesis. Therefore, it is necessary to explore new method to bring Ln³⁺ and dye molecule together. In Chapter 7 a simple method, ion-association, is brought forward, in which a binary complex anion ie. [Ln(β-diketone)₄]^- can ion-associate with a dye cation to form an ion-association complex ie. [Ln(β -diketone)₄]^-[dye cation]⁺ through Coulombe interaction. At the first step, a visible dye R6G cation is ion-associated with [Ln(TTA)₄]^-, leading toluminescence intensity increasing of Nd³⁺ and Er³⁺ by 8-fold and ²-fold respectively. The sensitization process for Nd³⁺ is briefly described as S₁→T₁→⁴F_9/2, ⁴F_7/2 dominated by Dexter mechanism. Also DCM which possesses chelating N atoms can coordinate lanthanide ion to form the complex like Nd(HFA)₃DCM. Though Nd(HFA)₃DCM has better performace than Nd(HFA)₃·2H₂O, DCM's sensitization behavior is not as good as R6G's totally.As reviewed in Chapter 2 and above-mentioned most dyes are visible ones for sensitization so that the excitation sources should be visible lasers that are high price and bulky. It is impossible to integrate visible lasers onto optical integrated circuit while NIR lasers that are usually made from semicondctors can be integrated. Hence, it is required to employ NIR dye to sensitize Ln³⁺ in order to take advantage of NIR semiconductor laser diodes. Here, sensitized emission of Er³⁺ by three similar NIR dyes, ie. IR140, IR27 and IR5, also has been the goal in Chapter 7. These NIR dyes have absorption peaks near 800 nm or 980 nm, which can employ 800 nm or 980 nm LD as excitation source. NIR dyes ion-associated with [Er(TTA)₄]^- or [Er(HFA)₄]^- to form Er(TTA)₄(IR140) Er(TTA)₄(IR27) and Er(HFA)₄(IR5). Singlet and triplet states of NIR dye cations in ion-association complexes are experimently determined. On 800 nm excitation, the luminescence intensity of Er(TTA)₄(IR140) is 6-fold of that of Er(TTA)₄K due to the existence of IR140 cation while the distance between [Er(TTA)₄]^-and [IR140]⁺ is deduced as 9±2 A experimentally. On 980 nm excitation, the luminescence intensity of Er(HFA)₄(IR5) is 10-fold of that of Er(HFA)₄K due to the existence of IR5 cation. Nevertheless, On 980 nm excitation, very weak signal is gotten from Er(TTA)₄(IR27). And on 488 nm excitation, the luminescence intensity of Er(TTA)₄(IR27) is 3-fold of that of Er(TTA)₄K due to the existence of IR27 cation. All these studies provide the possibility to employ NIR semiconductor as amplifier excitation source when using them as active doping.