Synthesis And Luminescence Properties Of Rare-earth Poly-borates

Borates are widely used as inorganic function material due to their exceptionalphysicochemical properties and diverse structure types. Especially in the field of optical,because of the characteristics of rare earth borate,wide transparency region, highluminescent efficiency and optical damage resistance threshold, rare earth borates arewidely used for UV excitation fluorescent material matrix. However, the study ofhydrated rare earth borates and anhydrous poly-borates fluorescent material in the rareearth borates system are still limited. In our study, the synthesis conditions of fivesystems hydrated rare earth borates were defined and photo-luminescent properties werealso investigated; two kinds of anhydrous rare earth penta-borates were gained bythermal decomposition and Sol-gel method, the PL properties werealsoinvestigated.The main experiment results are as follow:1.The synthesis conditions of Sm[B9O13(OH)4]·H2O、 Gd[B6O9(OH)3]、La[B5O8(OH)2]·1.5H2O、 La[B8O11(OH)5] and Gd[B20O30(OH)9] and the dopingconcentrate uplimit of Eu3+were investigated. Additionally, two kinds of anhydrous rareearth penta-borates by annealing thesehydrated rare earth borates were obtained.2. PL properties of Sm1-xEux[B9O13(OH)4]·H2O(x=0.09-1) and their dehydratedproductsα-Sm1-xEuxB5O9(x=0-1.00)were investigated systematically. The main resultsare given as follows:①. Eu3+and Sm3+are basically separated luminescent activators. Comparatively,Sm3+shows a very small emission intensity, which was ignoredreasonably, sothe studywas forced on the luminescence afterEu3+doping.②. There is no quenching effect in those poly-borates, because the large borateionic groups isolate the Eu3+activators very well.③.Three weight–loss steps for Eu[B9O13(OH)4]·H2O and a re-crystallizationprocess to α-EuB5O9were observed base on TG-DSC and powder XRD experiments.Meanwhile, the luminescent spectra of Eu3+were reccorded, which shows an interestingvariety and was used as a good medium to study the coordination environmentevolutionof Eu3+, even for the intermediate amorphous. In fact, the coordination symmetry ofEu3+in the amorphous state is the lowest.The high efficiency of the f-ftransitions andlarge R/O value (3.8) imply this amorphous phase is potentially a good red-emittingUV-LDE phosphor. Moreover, anhydrous α-EuB5O9shows the highest luminescent efficiency excited by Eu3+CT transition.④.In addition, α-Sm1-xEuxB5O9was synthesized bysol-gel method directly for thefirst time, and α-EuB5O9shows superior PL properties due to its better crystallinity.3. The luminescent properties of Gd1-xEux[B6O9(OH)3](x=0-1.00) and theirdehydrated products α-Gd1-xEuxB5O9were also investigated:①.Efficient energy transfer from Gd3+to Eu3+was found in all of the studiedpoly-borates, and there is no quenching effect in those studied poly-borates.②.Base on the results of TG-DSC and powder XRD, weobserved the dehydrationof Eu[B6O9(OH)3], the re-crystallization to α-EuB5O9and future decompositiontoα-EuB3O6. During those processes, spectra show interesting various, indicating theluminescence of Eu3+is a good medium to understand the coordination environmentevolution of Eu3+. The symmetry of the Eu3+coordination environment is the lowest inthe amorphous state. Interestingly, this amorphous phase possessesefficientf-f transitionsand a large R/O value (4.0), which implies it is a good red-emitting UV-LED phosphorcandidate. Moreover, anhydrousα-EuB5O9shows the highest luminescence efficiencywhen excited by Eu3+CT transition.③. For the first time, complete solid solution α-Gd1-xEuxB5O9were synthesizeddirectly by sol-gel method, and their luminescence properties were also studied, whichshowingsuperior PL properties than the products obtained by thermal decompositionmethod.4. The PL properties of La1-xEux[B5O8(OH)2]·1.5H2O （x=0-0.20） and theirdehydrated productsβ-La1-xEuxB5O9were studied. The luminescence intensity increaseswith the doping concentration up to x=13%in the compoundsLa1-xEux[B5O8(OH)2]·1.5H2O and x=15%in the compoundsβ-La1-xEuxB5O9, respectively.Then, a decline of the luminescence intensity was observed. Such low quenchingconcentrations are related to the structural distortion induced by the substitution ofLa3+byEu3+.However, all compounds possess large R/O, which implies their potentialapplication as good red UV-LED phosphors.