The Fabrication of Nano-Particles in Aqueous Solution From Oxyfluoride Glass Ceramics by Thermal Induction and Corrosion Treatment
© to the authors 2008
Received: 6 July 2008
Accepted: 3 October 2008
Published: 25 October 2008
An innovative route is reported to fabricate nano-particles in aqueous solution from oxyfluoride glass by the thermal induction and corrosion treatment in this letter. The investigations of X-ray diffraction and transmission electron microscope based on nano-particles in glass ceramics (GCs) and aqueous solution indicate that the nano-particles formed in glass matrix during the thermal induction process are released to aqueous solution and their structure, shape and luminescent properties in glass host can be kept. Owing to the designable composition of the nano-particles during glass preparation process, the method is a novel way to obtain nano-particles in aqueous solution from GCs.
KeywordsNano-particles Glass ceramics Thermal induction and corrosion treatment
Since Wang and Ohwaki  reported that transparent oxyfluoride glass ceramics (GCs) showed more efficient upconversion (UC) from infrared to visible than fluoride glass in 1993, many researchers have paid attention to oxyfluoride GCs. [2–5] The advantages of these materials are that the rare earth (RE) ions can be incorporated selectively in the fluoride crystal phase with lower phonon energy after thermal induction and the materials remain transparent due to the nano-scale size of precipitated crystals much smaller than the wavelength of visible light.
Unlike multiphoton absorption in organic dyes or semiconductor quantum dots (QDs), photon UC involves real intermediate quantum states to generate efficient visible light by near infrared (NIR) excitation. High-efficient luminescent intensity, adjustable size, narrow size distribution and unique optical properties are helpful to practical applications of UC materials, especially RE-ion-doped inorganic nano-particles after heat-treatment, in the fields of flat-panel display, light-emitting diodes, temperature sensors, biolabels, DNA detection, photodynamic therapy, etc [6–10]. Moreover, different nano-particles composition could be designed in glass matrix [11–14]. Unfortunately, ever since the first report on oxyfluoride GCs, there have been much research on the properties of nano-particles in GCs but no publication has been reported about how to obtain free nano-particles in aqueous solution from the GC-host and how to apply it to the fields mentioned above, especially in biological field. Therefore, it is of great significance to develop convenient routes to fabricate inorganic nano-particles doped RE-ion in aqueous solution from GCs in order to meet their practical application requirements.
Silicate oxyfluoride glass is selected here and (Pb,Cd)F2:Er3+,Yb3+nano-particles were formed in glass matrix after thermal induction. Acid corrosion treatment was employed to remove the glass matrix in order to obtain free (Pb,Cd)F2:Er3+,Yb3+nano-particles in aqueous solution. The UC emissions of (Pb,Cd)F2:Er3+,Yb3+nano-particles in aqueous solution have been well characterized by pumping the intermediate4I11/2state of the Er3+ion via a facile 980 nm NIR diode laser. The 980 nm excitation wavelength is fairly transparent for most large biomolecules and does no damage to them. The UC emissions of (Pb,Cd)F2:Er3+,Yb3+nano-particles in aqueous solution are convenient to observe. Additionally, different nano-particles composition and different RE-ion-dope can be employed for cellular and intracellular target.
Oxyfluoride glasses with composition of 45.5SiO2–40PbF2–10CdF2–0.5Er2O3–4Yb2O3 were prepared. About 20 g of starting material were fully mixed and melted in a covered platinum crucible in air atmosphere at 1,000 °C for 2 h, and then cast into a steel plate. [1–5] To obtain nano-particles in glass ceramic, the glass samples were subsequently heat-treated at 470 °C for 8 h at the nucleation temperature measured by differential thermal analysers (DTA). Using DTA equipment (TA-Inst 2100), samples were held in a Pt crucible and analysed against a calcined Al2O3 reference at a heating rate of 20 °C min−1.The nano-particles in aqueous solution were fabricated with the following method. Firstly, the GCs (about 500 mg) were immersed into 5.65 mol/L hydrofluoric acid for 20 h to get rid off silicate glass host. After corrosion treatment, the nano-particles were deposited by solid–liquid separation. Then pH value was adjusted to neutrality by repeated adding distilled water. Finally, the nano-particles in aqueous solution were dispersed using sodium lauryl benzenesulphate. A small quantity of the dried nano-particles powder was used for X-ray diffraction (XRD) measurements, while a dilute solution of the dispersed powder in distilled water was used for fluorescent and shape studies. XRD analysis were performed to identify the crystallization phase with a power diffractometer (D/Max-2500), using CuKα as the radiation. The scan range was 5–85° with a step size of 0.02°. Fluorescent spectra were measured with SPEX Fluorolog-2 Spectrofluorimeter (with error ± 0.2 nm), in which 980 nm semiconductor laser is the excitation source and a photo-multiplier tube is the detector. In order to compare the intensity of the luminescence of all the samples as accurately as possible, the position and power of the pumping beam and the width of the slit to collect the luminescence signal were fixed under the same conditions. All the measurements were carried out at room temperature. The preparation and measurement process for all samples are the same conditions.
Results and Discussion
From a practical point of view, it is possible for the nano-particles in aqueous solution from the GC-host to have a potential application as nano-sized probes used in the drug targeting after appropriate modification during the exploration of cellular and intracellular targeting. Under ideal circumstances, nano-particles for site-specific drug delivery, mediated by a targeting sequence, should deliver their payload only to specific target cells, tissues or organs [9, 18]. Moreover, nano-particles may optimize the bioavailability and the bio-distribution of the drug. The nano-particles in aqueous solution from the GC-host also apply in non-invasive imaging by detecting the luminescence of nano-particles inside biological systems, like cells, tissues or whole organisms. The further work for digging out the properties and applications of the nano-particles in aqueous solution is under way.
In summary,β-(Pb,Cd)F2:Er3+,Yb3+nano-particles in aqueous solution were prepared by means of thermal induction to produce nano-particles in glass matrix and corroding the glass host by hydrofluoric acid. The nano-particles in aqueous solution have the same structure and luminescent properties as nano-particles existing in glass matrix. Although thermal induction and corrosion treatment were used to prepareβ-(Pb,Cd)F2:Er3+,Yb3+nano-particles in aqueous solution in this letter, it may directly apply to any other silicate GCs doped with other RE ions and embedded various composition of nano-particles, since the preparation method is based on a fundamental consideration.
The work is supported by the National Natural Scientific Foundation of China under Grant No. 10574074, 973 Program (No. 2007CB613403), the 111 Project (B07013), Changjiang Scholars and Innovative Research Team in University, the Cultivation Fund of the Key Scientific and Technical Innovation Project from the Ministry of Education of China under Grant No. 704012, Key International Science and technology Cooperation Project under award No. 2005DFA10170, and National College Students Innovation Project from the Ministry of Education of China under Grant No. NK0713. The authors also thank Cui Guoxin (Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Science) for many helpful suggestions.
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