Preparation And Luminescent Properties Of Bismuth Doped Phosphate/Germanate Glasses And Fibers

Bismuth?Bi?-doped glasses and optical fibers are considered as a potential gain medium for the fabrication of a new generation of fiber amplifiers and broadband tunable fiber lasers due to their super broadband near-infrared?NIR?luminescence?900-1700 nm?,which covers the entire low loss communication window of silica fiber.So far,the super broadband NIR luminescence of bismuth has been explored and realized in diverse glass systems.However,the following problems still seriously limit the development of bismuth fibers and devices:?1?The relationship is not clear between Bi NIR emission behaviors and glass structure;?2?The absorption are quite weak and the gain is really low in current Bi-doped silica fiber,which is caused by the extremely low doping concentration of bismuth;?3?None suitable Bi-doped laser glass composition can be used to prepare optical fiber by rod in tube method.In order to solve these problems,we chosed phosphate/germanate system as the research object and systematically investigated the relationship between Bi NIR emission and glass structure.Based on these,a new type of Bi-doped glass was obtained and a multi-component Bi-doped germanate glass fiber was subsequently fabricated by rod in tube methods,The main results are listed as follows:1.In view of the limitations of fiber drawing tower,at first,we chose Bi-doped zinc aluminophosphate glass with good fiber-forming properties and lower drawing temperatures.By changing the doping concentrations of alumina and zinc oxide,the aluminum coordination was transformed from AlO₄,AlO₅ to AlO₆,which led to the change of the number of bridging oxygen and the polymerization degree of glass network.The increase of AlO₄ in the glass can reduce the crystal field strength around bismuth,resulting in the tunable NIR emissions in the range of 1208-1260 nm.²⁷Al NMR,³¹P NMR,FTIR and NIR emission spectra of different glass components were analyzed comprehensively and revealed that higher polymerization degree is more beneficial to Bi NIR emission.2.To clarify the relationship between the glass structure and Bi emission,because of the sensitivity of bismuth to the surrounding environment,germanate and phosphate glasses were taken as the examples due to the huge structural difference between them.In the P₂O₅-GeO₂mixed system,we found the color of phosphate glass disappeared and emission intensity was reduced by 92 times with the addition of very few germanium oxide?0.1 mol.%?into phosphate glass host.As germanium oxide continued to increase to 78 mol.%,glass structure was regionally depolymerized and then polymerized with the transformation of Q³ PO₄?Q²/Q¹ PO₄ and AlO₆/AlO₅?AlO₄,the disappearance of?P-O-P?_s and the formation of?Ge-O-Ge?_as.Simultaneously,the bismuth emission intensity was decreased and then increased.In brief,the combination of these two glass networks is not beneficial to Bi NIR emission.3.By optimizing the glass composition according to above results,we selected barium gallium germanate multi-component glass to prepare fibers.In this glass system,highly doping content of bismuth?5 mol.%?and super broadband luminescence could be simultaneously achieved.The doping concentration is two orders higher then the reported Bi silica fibers.In the heating-cooling thermal cycle experiment,the emission intensity of bismuth was only attenuated by 6%,showing good resistance of this Bi-doped glass to thermal impact.When heat treated at glass softening and transition temperatures,glass could still be transparent,indicating that it matches with the rod-in-tube method.The preparation process was optimized to solve the problems such as bubbles and processing techniques.Through the design of cladding and core refractive index,we successfully prepared Bi-doped multi-component germanate glass fiber by rod-in-tube method.The fiber core diameter was10?m and cladding diameter was 125?m.The fibers exhibited super broadband NIR emission.