One-step Synthesis of Stable, Nontoxic, Orange Quantum Dots Fluorescent Powder

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1 Nanomaterials Nanotechnology ARTICLE One-step Synthesis Stable, Nontoxic, Orange Quantum Dots Fluorescent Powder Regular Paper Shuhong Xu *, Jin Shen, Zhaochong Wang, Jinhua Du, Chunlei Wang, Zengxia Zhao Yiping Cui Advanced Photonics Center, School Electronic Science Engineering, Southeast University, Nanjing, P. R. China *Corresponding author(s) Received 5 December 5; Accepted February 6 DOI:.577/669 6 Author(s). Licensee InTech. This is an open access article distributed under the terms the Creative Commons Attribution License ( which permits unrestricted use, distribution, reproduction in any medium, provided the original work is properly cited. Abstract Stable, nontoxic, aqueous Cu:ZnInSe quantum dots () have been synthesized using one-step method. Through controlling ph, the -mercaptopropionic acid (MPA), impurities Cu In, high-quality Cu:ZnInSe have been obtained. First, as-prepared Cu:ZnInSe have better thermal stability. The photoluminescence () intensity wavelength are not changed during long-time heating reflux. Besides, the synthesizing method is simple, raw materials are green. Cu:ZnInSe are perfect fluorescent powder. Keywords, Fluorescent Powder, Synthesis. Introduction Due to the high cytotoxicity Cd-contained, more Zncontained have attracted the attention people, such as doped Cu:ZnSe [, ], Ag:ZnSe [], Mn:ZnSe [4, 5]. Pure ZnSe, for their emission is in the ultraviolet range, could not be applied in light-emitting diode (LED) quantum dots sensitized solar cell (QDSSC) fields. There are many problems for doped ZnSe. The first one is that the stability doped ZnSe is weak, which is caused by the lattice mismatch the impurities. As we know, the lattice mismatch would result in metal impurities tending to present on the surface make photoluminescence () quenched easily when they are applied in various fields [6]. Recently, our group has reported internally doped Cu:ZnSe in aqueous solution improved the stability Cu:ZnSe ZnS shell [7]. Besides, we have found that the excellent stability as-prepared is attributed to the simultaneous preparation core-shell internally doped impurities. At the same time, the mechanism for the stability internally doped Cu:ZnSe aqueous has been investigated [8]. The second one is that the synthesizing method is complex, which is difficult to apply in mass production. Thus, it is important to develop a new simple method to bulk-producing stable doped ZnSe aqueous. In this paper, Cu-doped ZnInSe have been synthesized in aqueous. The synthesizing method is simple, which can be used for mass production. Besides, doped Cu:ZnInSe have good stability for the intervention In. Thus, the as-prepared Cu:ZnInSe may be used as luminescent layer LED, i.e., fluorescent powder. Nanomater Nanotechnol, 6, 6:5 doi:.577/669

2 . Experimental Section. Synthesis Cu In co-doped ZnSe All materials used in this work were analytical reagents. Zn(NO ) CuCl were purchased from Sinopharm Chemical Reagent Co., Ltd. NaBH 4 was purchased from Guangdong Chemical Reagent Engineering Technological Research Development Center. NaOH was purchased from Shanghai Zhongshi Chemical Company. -mercaptopropionic acid (MPA), In(NO ) 6H O, Se powder were purchased from Aldrich. NaHSe solution was prepared using Se NaBH 4 according to the reference methods [9, ]. Aqueous Cu In co-doped ZnInSe were synthesized according to our previous work []. Zn(NO ), AgNO, In(NO ), MPA mixture were adjusted to ph using NaOH solution ( concentration 5mol/L). Freshly prepared NaHSe solution was injected into the mixture after the solution was aerated N for about min. Then, the solution was refluxed at C. The total concentration Zn in the mixture is. mol/l.. Characterization absorption (UV) were recorded a Shimadzu 6 near-infrared spectrophotometer. Fluorescence experiments decay experiments were performed an Edinburg FLS 9 spectrluorimeter. The excitation wavelength was 6 nm. All optical measurements were performed at room temperature under ambient conditions. X-ray photoelectron spectroscopy (XPS) was investigated using a PHI55 spectrometer Mg Kα excitation (5.6 ev). Binding energy calibration was based on C s at 84.6 ev. X-ray powder diffraction (XRD) investigation was carried out using the D/max-5/ PC diffractometer CuKα radiation (λ=.548å). For XPS XRD measurement, Cu:ZnInSe powder were used. To obtain the powder, freshly prepared were precipitated from solution by addition equal volume isopropanol [] then dried at vacuum. Fluorescent images cells were taken on an Olympus FluoView FV fluorescence microscope.. Results Discussion. The influence ph, the MPA, the ratio raw materials Both the intensity the range wavelength are related to ph value, lig, impurities. The following has obtained the optimal experimental data through comparing the change absorbance at condition. First, the absorbance Cu:ZnInSe ph are shown in. solution Cu:In:Zn:MPA:Se being.:.:::. have grown for Nanomater Nanotechnol, 6, 6:5 doi:.577/669 hours at ph 7., 8., 9.,.,.. There is little influence ph on absorption, showing that ph does not influence the size. However, the influence ph on the intensity is obvious. For the intensity, it is at ph 7., 8., 9.,.,.. At ph 8., the intensity is the strongest. The positions peaks are almost at the same location, which is consistent the results the absorption. For the samples at ph 7., 8., 9.,.,., they have the same absorption. Namely, ph solution has little influence on the size ph7. ph7. ph8. ph8. ph9. ph9. ph. ph. PH RL Intensity (a.u.) MPA-capped MPA-capped Cu:ZnInSe Cu:ZnInSe ph ph values values 7., 7., 8., 8., 9., 9.,.,., is relative.... The The (RL) intensity intensity intensity. is is relative relative (RL) (RL) intensity. intensity. MPA MPA 77uL MPA 54uL MPA 78uL MPA 46uL MPA-capped Cu:ZnInSe MPA 77, 77, 54, 78, 46 ul. Intensity(a.u.) Intensity(a.u.) RL Second, the absorbance Cu:ZnInSe lig (MPA 77, 54, 78, 46 ul) are shown in. lig solution (MPA Cu:In:Zn:Se 77, being 54,.:.::. 78, ph 8. have grown for hours. Clearly, the MPA has influence on the absorption. 46 ul) are shown in. solution Seen from the absorbance, increasing the MPA from 54 to to 46 ul, the Cu:In:Zn:Se being.:.::. ph 8. have grown for absorption shift to blue. Blue shift absorption may be caused by quantum size effect. Namely, hours. increasing Clearly, the the MPA, the size MPA Cu:ZnInSe has influence becomes small. on For the sample absorption MPA 77 ul, there is obvious. aggregation Seen in solution. from In addition, the the absorbance intensity increases from 77 to 54 ul decreases from 54 to 46 ul. Thus, the optimal, increasing the MPA from 54 to MPA for Cu:ZnInSe is 54 ul. 5 6 ph ph ph ph ph ph ph ph.. ph ph... MPA-capped Cu:ZnInSe ph values 7., 8., 9.,.,.. The intensity MPA MPA 77uL 77uL MPA MPA 54uL 54uL MPA MPA 78uL 78uL MPA MPA 46uL. MPA-capped Cu:ZnInSe MPA 77, 54, 78, 46 ul Second, the absorbance Cu:ZnInSe 46 ul, the absorption shift to blue. Blue shift absorption may be caused by quantum size effect. Namely, increasing the MPA, the size Cu:ZnInSe becomes small. For the sample MPA 77 ul, there is obvious aggregation in solution. In addition, the intensity increases from 77 to 54 ul decreases from 54 to 46 ul. Thus, the optimal MPA for Cu:ZnInSe is 54 ul. Cu ul Cu ul Cu 4uL Cu 8uL RL Intensity(a.u.) Third, the absorbance Cu:ZnInSe impurity Cu (,, 4, 8 ul) are shown in. solution In:Zn:MPA:Se being.:::. ph 8. have grown for hours. Absorbance shift to red increasing the Cu. It is to say that the Cu has influence on the size ZnSe. However, the difference size is so small that could not be showed in transmission electron microscopy (TEM), high-resolution (HR) TEM. As for, the intensity is decreasing increasing the Cu. When the Cu is zero, there is no luminescence for ZnInSe. Thus, impurity Cu takes important role in Cu:ZnInSe. In fact, the energy bs In ZnSe are not matched. The energy b Cu is matched Cu ul Cu ul Cu 4uL Cu 8uL. MPA-capped Cu:ZnInSe. MPA-capped Cu:ZnInSe Cu. Cu

3 In are the same but their intensity is. The peaks Cu:ZnInSe are at 56 nm for Cu:ZnInSe Cu ul Cu the ul In 4, 6, 8, ul. However, when the In is lower than 4 ul, Cu the ul peak position Cu:ZnInSe has been shifted to blue, Cu ul 4 which is emission Cu:ZnSe Cu (the 4uL dotted line black line in 4b). Therefore, the range Cu 4uL In at Cu:ZnInSe is Cu from 8uL 4 to 6 ul. Cu 8uL Third, the absorbance Cu:ZnInSe 8 impurity Cu (,, 4, In 4uL In 4uL In 6uL In 6uL In 8uL 6 In 8uL 8 ul) are shown in. solution In ul In ul In:Zn:MPA:Se being.:::. ph 8. have grown for 4 hours. Absorbance shift to red increasing the Cu. It is to say that the Cu has influence on the size ZnSe. However, the difference size is so small that could not be showed in transmission electron microscopy. (TEM), high-resolution MPA-capped (HR) TEM. Cu:ZnInSe As 4. Cu. MPA-capped Cu:ZnInSe 4. MPA-capped Cu:ZnInSe In. The for, the intensity is decreasing In. The dotted line black line in are Third, the absorbance Cu:ZnInSe dotted line black Cu:ZnInSe line impurity in are Cu (, Cu:ZnInSe, In ul. In ul. increasing the Cu. When the Cu is 4, 8 ul) are shown in. solution In:Zn:MPA:Se.. Stability being an.:::. application Cu:ZnInSe ph 8. zero, there is no luminescence for ZnInSe. Thus, have grown for hours. Absorbance shift to red increasing Cu:ZnInSe the synthesized under Cu. ph It 8. is to Cu:In:Zn:MPA:Se say being.:.:::. condition have impurity Cu takes important role in Cu:ZnInSe. In fact,. Stability an application Cu:ZnInSe the energy that the bs In Cu has influence ZnSe are on the not size matched. ZnSe. TheHowever, the difference size is so small energy that b could not Cu be is showed matched in transmission ZnSe electron In. microscopy Thus, Cu (TEM), changed Cu:ZnInSe high-resolution when they are applied (HR) in LED TEM. synthesized As QDSSC. for And even under the emission ph color 8. is changed is the bridge, energy the intensity bs is ZnSe decreasing In (Scheme increasing ). At the Cu:In:Zn:MPA:Se Cu. When the being.:.:::. Cu condition have 547 nm) after refluxing lasted 7 hours ( 5). Moreover, intensity Cu:ZnInSe increased first, impurity is zero, there Cu is captures no luminescence the hole for ZnInSe ZnSe.. Then, Thus, the impurity hole Cu good takes important thermal stability role in Cu:ZnInSe high quantum yields (7%). As the growth time from to 9 hours. Then, the intensity keeps in this data. After refluxing for in energy. In b fact, the energy Cu is bs captured In by ZnSe impurity are not In. matched. The The energy we have b known, Cu is matched have quantum size effect. For emission ZnSe is from In. the Thus, conduction Cu is the bridge b energy ZnSe bs to impurity aqueous, their size increase growth time. In this ZnSe In (Scheme ). At first, impurity Cu field LED. b captures In. Comprehensive the hole ZnSe. consideration Then, the hole in the energy b intensity way, the wavelength has been changed when Cu is captured by impurity In. The emission function impurity Cu, the optimal Cu they are applied in LED QDSSC. And even the is from the conduction b ZnSe to impurity b In. Comprehensive consideration the is ul. emission color is changed under room temperature. intensity function impurity Cu, the optimal Cu is ul. For Cu:ZnInSe, the wavelength peaks has little change (from 558 to 547 nm) after refluxing lasted 7 hours ( 5). Moreover, intensity Cu:ZnInSe increased the growth time from to 9 hours. Then, the intensity keeps in this data. After refluxing for about 7 hours, intensity begins to reduce. Thus, Cu:ZnInSe have good thermal stability. The peak position is stable, intensity keeps stable under refluxing, which is important for application field LED. RL Intensity(a.u.) have grown for hours. The In has little influence on the absorbance. Namely, the In does not influence the growth. The shapes for Cu:ZnInSe Intensity(a.u.) good thermal stability high quantum yields (7%). As we have known, have quantum size effect. For aqueous, their size increase growth time. In this way, the wavelength has been under room temperature. For Cu:ZnInSe, the wavelength peaks has little change (from 558 to about 7 hours, intensity begins to reduce. Thus, Cu:ZnInSe have good thermal stability. The peak position is stable, intensity keeps stable under refluxing, which is important for application h h 5h 7h 9h h 5h 9h h 4h 6h 8h h h 7h RL Intensity(a.u.) 8 h 6 h 5h 7h 4 9h h 5h 9h h 4h 6h 8h h h 7h Sheme. Schematic illustration the possible relationship among the Wavelngth(nm) energy b Sheme. Cu:ZnInSe Schematic illustration the possible relationship among the energy b Cu:ZnInSe. 56 Fourth, the absorbance Cu:ZnInSe impurity In (4, (c) 6, Fourth, the absorbance Cu:ZnInSe 8, ul) are shown in 4. solution Cu:Zn:MPA:Se 555 being.:::. ph 8. impurity In (4, 6, 8, ul) are shown in 4. solution Cu:Zn:MPA:Se being.:::. ph 8. have grown for hours. The In has little influence on the absorbance. Namely, the In does not influence the growth. The shapes for Cu:ZnInSe In are the same but their intensity is. The peaks Cu:ZnInSe are at 56 nm for Cu:ZnInSe the In 4, 6, 8, ul. However, when the In is lower than 4 ul, the peak position Cu:ZnInSe has been shifted to blue, which is emission Cu:ZnSe (the dotted line black line in 4b). Therefore, the range In at Cu:ZnInSe is from 4 to 6 ul. Peak Wavelength (nm) Time (h) (d) 5 5 Time (h) 5. Time-dependent 5. Time-dependent MPA-capped Cu:ZnInSe. Time-dependent MPAcapped peak Cu:ZnInSe intensity (c). peak Time-dependent position (d) MPA-capped normalized Cu:ZnInSe. peak intensity (c) normalized In addition, Cu:ZnInSe peak position are easy (d) to deposit MPA-capped to obtained powder Cu:ZnInSe (. 6, left). Under the optimal condition, synthesized Cu:ZnInSe are deposited using centrifugal machine lower rotation rate. Moreover, In addition, the productivity Cu:ZnInSe /QD-solution are easy is g/ to ml. deposit Cu:ZnInSe to obtained powder has good characters. The powder has good crystal type atom mole rate. XRD data Cu:ZnInSe powder ( 6, left). Under the optimal condition, synthesized under ph 8. Cu:In:Zn:MPA:Se being.:.:::. condition are depicted in 6. The synthesized peaks Cu:ZnInSe Cu:ZnInSe are the same, are, deposited ZnSe. The using impurities centrifu have not changed the lattice ZnSe, which may be the reason Cu:ZnInSe having good stability. gal machine lower rotation rate. Moreover, the productivity Cu:ZnInSe /QD-solution is g/ ml. Cu:ZnInSe powder has good characters. The Intensity Absorbance Shuhong Xu, Jin Shen, Zhaochong Wang, Jinhua Du, Chunlei Wang, Zengxia Zhao Yiping Cui: One-step Synthesis Stable, Nontoxic, Orange Quantum Dots Fluorescent Powder Counts Peak Intensity (a.u.) () () () Cubic bulk ZnSe

4 powder has good crystal type atom mole rate. XRD data Cu:ZnInSe synthesized under ph 8. Cu:In:Zn:MPA:Se being.:.:::. condition are depicted in 6. The peaks Cu:ZnInSe are the same,, ZnSe. The impurities have not changed the lattice ZnSe, which may be the reason Cu:ZnInSe having good stability. is doped into ZnSe. The Cu In in Cu:ZnInSe is lower, but there is obvious peaks in XPS figure. The change Zn:Se:S ratio between experimental data raw atomic rate is caused by the excessive addition Zn in raw. Seeing from the peak positions XPS, the valent state Cu In is + +. In addition, TEM HRTEM figures ( 8) show that Cu:ZnInSe are about.5 nm. Absorbance 4. Conclusions Intensity Counts Left: 6 absorption 7 8 Cu:ZnInSe synthesized under 4 ph 5 8. Cu:In:Zn:MPA:Se being Wavelength.:.:::. condition. (nm) Inset image is a photo Cu:ZnInSe powder under the irradiation a UV lamp. (degree) Right: XRD Cu:ZnInSe powder under the above condition. () () () Cubic bulk ZnSe 6. XPS Left: data Cu:ZnInSe absorption powder are depicted in 7. The experimental data Cu:ZnInSe Cu:In:Zn:Se:S are synthesized.:.::.5:.74, under ph which 8. are similar to Cu:In:Zn:MPA:Se the raw atomic rate (.:.:::.). being It is.:.:::. to say that total Cu raw is doped into ZnSe. The in Cu:ZnInSe is lower, but there is condition. Inset image is a photo Cu:ZnInSe powder under the obvious peaks in XPS figure. The change Zn:Se:S ratio between experimental data raw atomic rate irradiation a UV lamp. Right: XRD Cu:ZnInSe powder under the is caused by the excessive addition Zn in raw. Seeing from the peak positions XPS, the valent state above condition. Cu In is + +. In addition, TEM HRTEM figures ( 8) show that Cu:ZnInSe are about.5 nm. Intensity(ps) 4 Cu:In:Zn:Se:S=.:.::.5: Se Cu XPS 7. XPS (right) Cu:ZnInSe Cu:ZnInSe synthesized under ph synthesized 8. Cu:In:Zn:MPA:Se under being.:.:::. ph 8. Cu:In:Zn:MPA:Se condition. being.:.:::. condition In Aqueous nontoxic Cu:ZnInSe powder good stability has been synthesized using one-step method. First, influence ph, the MPA, impurities has been investigated. On this basis, high-quality Cu:ZnInSe have been obtained good thermal stability. The intensity wavelength are not changed during longtime heating reflux. Second, Cu:ZnInSe powder has been obtained simple method. The synthesizing process purification method, raw materials are green. Thus, Cu:ZnInSe powder has potential application in LED field as fluorescent powder. 5. Acknowledgements This work is supported by the National Key Basic Research Program China (Grant No. 5CB5), National Natural Science Foundation China (Grant Nos , 44, 677), the Fundamental Research Funds for the Central Universities (No. 44R6), the natural science foundation Jiangsu Province Youth Fund (No. BK465), China Postdoctoral Science Foundation (No. 4M567, 5T8477), Jiangsu Planned Projects for Postdoctoral Research Funds (No. 45B). 6. References 8. TEM HRTEM (inset) Cu:ZnInSe under ph 8. Cu:In:Zn:MPA:Se being.:.:::. condition. The scale bars are nm (TEM) 4 nm (HRTEM) XPS data Cu:ZnInSe powder are depicted in 7. The experimental data Cu:In:Zn:Se:S are.:.::.5:.74, which are similar to the raw atomic rate (.:.:::.). It is to say that total Cu In raw [] Han J S, Zhang H, Tang Y, et al. Role redox reaction electrostatics in transition-metal impurity-promoted photoluminescence evolution water-soluble ZnSe nanocrystals. Journal Physical Chemistry C, 9, (8): [] Gao X, Wang C, Niu L, et al. Aqueous synthesis Cu-doped ZnSe quantum dots. Journal Luminescence,, (7): 4. [] Xu SH, Wang CL, Sun QF, et al. Water-soluble Ag:ZnSe nanocrystals excellent stability via internal doping donor-type cation impurity. Materials Research Express, 4, :5. [4] Zhang H, Gao X, Liu S Y, et al. One-pot synthesis stable water soluble Mn:ZnSe/ZnS core/shell quantum dots. Journal Nanoparticle Research,, 5(6):749. [5] Gao X, Zhang H, Li Y, et al. Mn-doped ZnSe d-dotsbased alpha-methylacyl-coa racemase probe for human prostate cancer cell imaging. Analytical Bioanalytical Chemistry,, 4(5): Nanomater Nanotechnol, 6, 6:5 doi:.577/669

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