CAJ | 학술논문

以乙二胺四乙酸（EDTA）为螯合剂，用一种改进的共沉淀法制备了 Yb3＋/Er3＋共掺的立方相NaYF4和Yb3＋/Er3＋/Gd3＋三掺的六角相NaYF4纳米晶。用透射电子显微镜、X射线衍射、荧光光谱等测量手段对样品的形貌、晶相和发光性能进行了表征。结果表明，通过掺杂Gd3＋，实现了NaYF4基质从立方相到六角相的相变。虽然据报道六角相的NaYF4比立方相的NaYF4上转换效率高，但是相变对上转换荧光光谱的影响还不清楚。本文着重研究了相变对晶格场能级分裂、发光强度和发光颜色的调控作用，提出了荧光增强和发光颜色可调的机理。用10 mW ，980 nm二极管激光激发，在立方相和六角相样品中均观察到肉眼可见的上转换荧光发射，分别是525/550 nm附近2 H11/2/4 S3/2→4 I15/2跃迁引起的绿光发射和657 nm附近4 F9/2→4 I15/2跃迁引起的红光发射。与立方相样品相比，六角相样品荧光发射谱线变窄，荧光强度增强了一个量级，出现了2 H9/2→4 I13/2跃迁引起的新发射峰，红绿比由2∶1增大到3∶1，这是因为六角相基质的晶格场对称性降低，于是增强了上转换荧光强度，同时六角相的晶胞体积变小，提高了掺杂离子周围的晶格场强度，导致发射谱线变锐，表明相变可以调节晶格场能级分裂，发光强度和发光颜色。
이을이알사을산（EDTA）위오합제，용일충개진적공침정법제비료 Yb3＋/Er3＋공참적립방상NaYF4화Yb3＋/Er3＋/Gd3＋삼참적륙각상NaYF4납미정。용투사전자현미경、X사선연사、형광광보등측량수단대양품적형모、정상화발광성능진행료표정。결과표명，통과참잡Gd3＋，실현료NaYF4기질종립방상도륙각상적상변。수연거보도륙각상적NaYF4비립방상적NaYF4상전환효솔고，단시상변대상전환형광광보적영향환불청초。본문착중연구료상변대정격장능급분렬、발광강도화발광안색적조공작용，제출료형광증강화발광안색가조적궤리。용10 mW ，980 nm이겁관격광격발，재립방상화륙각상양품중균관찰도육안가견적상전환형광발사，분별시525/550 nm부근2 H11/2/4 S3/2→4 I15/2약천인기적록광발사화657 nm부근4 F9/2→4 I15/2약천인기적홍광발사。여립방상양품상비，륙각상양품형광발사보선변착，형광강도증강료일개량급，출현료2 H9/2→4 I13/2약천인기적신발사봉，홍록비유2∶1증대도3∶1，저시인위륙각상기질적정격장대칭성강저，우시증강료상전환형광강도，동시륙각상적정포체적변소，제고료참잡리자주위적정격장강도，도치발사보선변예，표명상변가이조절정격장능급분렬，발광강도화발광안색。
Yb3+ /Er3+-co-doped cubic NaYF4 and Yb3+ /Er3+ /Gd3+-tri-doped hexagonal NaYF4 nanocrystals were synthesized by a modified coprecipitation method with ethylenediamine tetraacetic acid (EDTA) as chelating agent .The samples’ morphology , crystal phase and upconversion emission were measured with transmission electron microscope (TEM ) ,X-ray diffraction pat-terns (XRD) and upconversion luminescence spectrum .TEM and XRD results showed that the phase transition from cubic to hexagonal was promoted through Gd3+ doping .It has been reported that the upconversion efficiency of hexagonal NaYF4 is higher than that of cubic NaYF4 ,however ,the effect of crystal phase on upconversion luminescence has not been well under-stood .This work focuses analysis of measurement results to compare the effect of crystal phase on the crystal field energy split-ting and upconversion emission intensity as well as emission color ,and a mechanism of luminescence enhancement and color tun-ability are revealed .Strong visible upconversion luminescence can be seen clearly by the naked eyes in both cubic phase and hexa-gonal phase samples upon excitation by a 980 nm laser diode with power of 10 mW ,consisting of green emissions centered at a-round 525/550 nm originating from the transitions of 2 H11/2/4 S3/2 → 4 I15/2 and red emission at about 657 nm from 4 F9/2 to 4 I15/2 of Er3+ ions respectively .In comparison to cubic sample ,the hexagonal phase sample presented much stronger and sharper upcon-version luminescence ,whose emission efficiency was enhanced 10 times with an additional transition of 2 H9/2 → 4 I13/2 at 557 nm , furthermore ,the intensity ratio of red to green emission increased from 2∶1 to 3∶1 .Doping NaYF4 nanocrystals with Gd3+ i-ons induced the hexagonal-to-cubic phase transition and thus decreased the crystal symmetry ,consequently increased absorption cross-section and 4 f-4 f transition probabilities by relaxing forbidden selection rules ,resulting in stronger emission .In the mean time ,the decreasing unit-cell volume of the hexagonal phase increased the crystal field strength around the dopant ions and consequently led to that hexagonal phase samples present much sharper emission compared to cubic counterparts .It demonstrates that phase transition can tune crystal field energy splitting ,luminescence intensity and emission color .