Lanthanum based upconverting microrods and application thereof

Abstract

The present invention provides a monodispersed lanthanum based upconverting microrods comprising β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ and β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+, capped with oleic acid. The upconverting microrods, embedded in polymer matrices is used for making security tags and for sensing application. The process of preparation of the oleic acid capped upconverting microrods is also disclosed.

Claims

1. A monodispersed lanthanum based upconverting microrods selected from β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ and β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+, capped with an organic ligand consisting of oleic acid, for making security tags and for sensing applications, wherein the β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ comprises β-NaYF.sub.4:Yb.sup.3+ and Er.sup.3+ but not Gd.sup.3+ and has an aspect ratio in the range of 6 to 12, or wherein the β-NaYF.sub.4:Yb.sup.3+, Tm′ comprises β-NaYF.sub.4:Yb.sup.3+ and Tm.sup.3+ but not Gd.sup.3+ and has an aspect ratio in the range of 3 to 7, and wherein the microrods selected from β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ and β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+ have a length of 120.257 nm and 418.1457 nm respectively, and a width of 12.5412 nm and 83.9962 nm respectively.

2. A process for the preparation of monodispersed lanthanum based upconverting microrods selected from β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ and β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+, capped with an organic ligand consisting of oleic acid, for making security tags and for sensing applications, where the β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ comprises β-NaYF.sub.4:Yb.sup.3+ and Er.sup.3+ but not Gd.sup.3+ and has an aspect ratio in the range of 6 to 12, or wherein the β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+ comprises β-NaYF.sub.4:Yb.sup.3+ and Tm.sup.3+ but not Gd.sup.3+ and has an aspect ratio in the range of 3 to 7 the process comprising the steps of: a. mixing oleic acid, sodium hydroxide, absolute ethanol and water; b. adding a solution containing a mixture of lanthanum compounds and sodium fluoride to a reaction mixture of step (a); c. refluxing the reaction mixture of step (b) for a period in the range of 4 to 6 hrs at a temperature in the range of 160 to 180° C. and allowed to cool at room temperature; and d. heating the reaction mixture of step (c) for a period in the range of 50 to 60 hrs at a temperature in the range of 180 to 195° C., under nitrogen atmosphere, followed by drying to afford the oleate-capped lanthanum based upconverting microrods.

3. The process as claimed in claim 2, wherein the mixture of the lanthanum compounds of step (b) contains Yttrium(III) chloride hexahydrate (YCl.sub.3.6H.sub.2O), Ytterbium(III) Chloride Hexahydrate (YbCl.sub.3.6H.sub.2O) and Erbium(III) chloride hexahydrate (ErCl.sub.3.6H.sub.2O).

4. The process as claimed in claim 2, wherein the oleate-capped lanthanum based upconverting microrods are embedded in polymer matrices for making security tags that respond to different wavelengths and for sensing applications.

5. The process as claimed in claim 4, wherein the polymer matrices are selected from polydimethylsiloxane (PDMS), Ethylene propylene diene monomer (EPDM), Polyethylene oxide (PEO), Polystyrene (PS) and a natural silk scaffold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Powder X-ray powder diffraction (XRD) of β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ UCMR.

(2) FIG. 2: TEM image of β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ UCMR.

(3) FIG. 3: Emission spectrum of β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ microrods in PDMS film (1% of UCMR).

(4) FIG. 4: Powder XRD of β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+ UCMR.

(5) FIG. 5: TEM image of β-NaYF4:Yb.sup.3+, Tm.sup.3+ UCMR.

(6) FIG. 6: Emission spectrum of β-NaYF.sub.4Yb.sup.3+, Tm.sup.3+ microrods in PDMS film (1% of UCMR).

(7) FIG. 7: UCNP embedded PDMS film (The letter ‘N’ was made with NaYF.sub.4 (Er/Yb) (which emits green under NIR radiation), ‘C’ was made with an organic dye and ‘L’ was made with NaYF.sub.4 (Tm/Yb)(which emits blue under NIR radiation).

(8) FIG. 8: UCNP (NaYF.sub.4 (Er/Yb) embedded polypropylene fibre that shows visibly the green color under NIR light (the above image was taken without the NIR filter and hence it is white in color).

DETAILED DESCRIPTION OF THE INVENTION

(9) The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

(10) In view of above, the present invention provides a monodispersed lanthanum based upconverting microrods for making a security tags.

(11) In view of above, the present invention further provides a composition comprising lanthanum based upconverting microrods embedded in polymer matrices, process for preparation thereof and use of said composition for the preparation of security tags.

(12) In an embodiment, the present invention provides a mono dispersed lanthanum based upconverting microrods for use in security tags and sensing application.

(13) In preferred embodiment, said mono dispersed lanthanum based upconverting microrods are capped with oleic acid.

(14) In another preferred embodiment, said oleate-capped mono dispersed lanthanum based upconverting microrods are selected from β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ or β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+.

(15) In yet another preferred embodiment, the length of the microrods β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ and β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+ is 120.257 nm and 418.1457 nm respectively.

(16) In still another preferred embodiment, the width of the microrods β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ and β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+ is 12.5412 nm and 83.9962 nm respectively

(17) In another preferred embodiment, the aspect ratio of said microrods β—NaYF4:Yb.sup.3+, Er.sup.3+ is in the range of 6 to 12.

(18) In yet another preferred embodiment, the aspect ratio of said microrods β—NaYF.sub.4:Yb.sup.3+, Tm.sup.3+ is in the range of 3 to 7.

(19) In another embodiment, the present invention provides a process for the preparation of oleate-capped lanthanum based upconverting microrods, wherein said process comprising the steps of: a) mixing oleic acid, sodium hydroxide, absolute ethanol and water; b) adding a solution containing a mixture of lanthanum compounds and sodium fluoride (NaF) to reaction mixture of step (a); c) refluxing the reaction mixture of step (b) for the period in the range of 4 to 6 hrs at temperature in the range of 160 to 180° C. and allowed to cool at room temperature; d) heating the reaction mixture of step (c) for the period in the range of 50 to 60 hrs at temperature in the range of 180 to 195° C. followed by drying to afford oleate-capped lanthanum based upconverting microrods.

(20) In a preferred embodiment, said reflux in step (c) is carried out under nitrogen atmosphere.

(21) In another preferred embodiment, said mixture of lanthanum compound in step (b) contains Yttrium(III) chloride hexahydrate (YCl.sub.3.6H.sub.2O), Ytterbium(III) Chloride Hexahydrate (YbCl.sub.3.6H.sub.2O) and Erbium(III) chloride hexahydrate (ErCl.sub.3.6H.sub.2O).

(22) In yet another preferred embodiment, said mixture of lanthanum compound in step (b) contains Yttrium(III) chloride hexahydrate (YCl.sub.3.6H.sub.2O), Ytterbium(III) Chloride Hexahydrate (YbCl.sub.3.6H.sub.2O) and Thulium(III) Chloride Hexahydrate (TmCl.sub.3.6H.sub.2O).

(23) In still another preferred embodiment, said oleate-capped lanthanum based upconverting microrods are selected from β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ or β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+.

(24) In yet another embodiment, the present invention provides a composition comprising oleate-capped lanthanum based upconverting microrods embedded in polymer matrices.

(25) In a preferred embodiment, said polymer matrices is selected from polydimethylsiloxane (PDMS), Ethylene propylene diene monomer (EPDM), Polyethylene oxide (PEO), Polystyrene (PS) and natural silk scaffold.

(26) In another preferred embodiment, the composition is in the form of microrods, nanocrystal and their composites in polymer matrices and conjugation with different organic dye molecules for energy transfer processes that could be useful for sensing application.

(27) In yet another preferred embodiment, said oleate-capped lanthanum based upconverting microrods are selected from β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ or β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+.

(28) In still another embodiment, the present invention provides a composition comprising oleate-capped lanthanum based upconverting microrods embedded in polymer matrices for making a security tags that may respond to different excitation wave lengths and are may be useful for sensing application.

(29) Tm/Yb and Er/Yb doped microrods are utilized to create a pattern on PDMS film and the result is provided in FIG. 7. These microrods can be embedded into polymeric fibre efficiently (polypropylene fibre) and the emission features can be visualized (FIG. 7).

(30) A very small amount of UCNP is melt compounded into polypropylene, a thermoplastic fibre forming polymer, using a DSM twin screw microcompounder and successfully extruded into fibres of 25-30 micron diameter. UCNPs are found to be thermally stable under polymer melt-processing conditions and retained their function (FIG. 8).

EXAMPLES

(31) Following examples are given by way of illustration therefore should not be construed to limit the scope of the invention.

Example 1

Synthesis of Oleate-Capped β-NaYF.SUB.4.: Yb.SUP.3+., Er.SUP.3+

(32) In a 100 mL two-neck round-bottom flask equipped with a water-cooled condenser, oleic acid (20 mL), sodium hydroxide (1.16 g), absolute ethanol (7 mL) and DI water (9 mL) were mixed together, to which an aqueous solution of 7 mL containing YCl.sub.3.6H.sub.2O, YbCl.sub.3.6H.sub.2O, ErCl.sub.3.6H.sub.2O (1 mmol in total, molar ratio 78:20:2) and NaF (5 mmol) were added under vigorous stirring. The reaction mixture was heated to boiling and refluxed for 6 h at 180° C. under N.sub.2 gas atm. Then solution was cooled to room temperature transferred into a Teflon bottle (100 mL) held in a stainless steel autoclave. It was sealed and hydrothermally heated at 195° C. for 60 h. After complete the reaction cooled to room temperature. 20 mL of absolute ethanol was added before and after hydrothermal treatment. Then the precipitate was separated by using centrifuged 10,000 rpm in 10 mins and washed with absolute ethanol (three times). Then the precipitate was dried in oven for 4 h.

(33) FIG. 1 shows Powder X-ray powder diffraction (XRD) of β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ UCMR.

(34) FIG. 2 shows TEM image of β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ UCMR.

(35) FIG. 3 shows Emission spectrum of β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ microrods in PDMS film (1% of UCMR).

Example 2

Synthesis of Oleate-Capped β-NaYF.SUB.4.:Yb.SUP.3+., Tm.SUP.3+

(36) In a 100 mL two-neck round-bottom flask equipped with a water-cooled condenser, oleic acid (20 mL), sodium hydroxide (1.16 g), absolute ethanol (7 mL) and DI water (9 mL) were mixed together, to which an aqueous solution of 7 mL containing YCl.sub.3.6H.sub.2O, TmCl.sub.3.6H.sub.2O (1 mmol in total, molar ratio 75:25:0.003) and NaF (5 mmol) were added under vigorous stirring. The reaction mixture was heated to boiling and refluxed for 6 h at 180° C. under N.sub.2 gas atm. Then solution was cooled to room temperature transferred into a Teflon bottle (100 mL) held in a stainless steel autoclave. It was sealed and hydrothermally heated at 195° C. for 60 h. After complete the reaction cooled to room temperature. 20 mL of absolute ethanol was added before and after hydrothermal treatment. Then the precipitate was separated by using centrifuged 10,000 rpm in 10 mins and washed with absolute ethanol (three times). Then the precipitate was dried in oven for 4 h.

(37) FIG. 4 shows Powder XRD of β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+ UCMR.

(38) FIG. 5 shows TEM image of β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+ UCMR.

(39) FIG. 6 shows Emission spectrum of β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+ microrods in PDMS film (1% of UCMR).

Example 3

Aspect Ratio of Said Micro Rods

(40) The aspect ratios of said micro rods are summarized in table 1.

(41) TABLE-US-00001 TABLE 1 β-NaYF.sub.4:Yb.sup.3+, Er.sup.3+ β-NaYF.sub.4:Yb.sup.3+, Tm.sup.3+ 8.7249 3.4794 7.6638 6.2082 11.5339 4.0016 8.1962 3.8283 8.0068 5.2400 8.9785 5.3537 9.0285 5.3591 9.3364 5.6863 9.9895 5.6188 9.7580 5.9735

Example 4

PDMS Film Containing UCMR

(42) 1 mg of UCNPs (NaYF.sub.4: Yb.sup.3+, Er.sup.3+/Tm.sup.3+) were dissolved in 1 mL of cyclohexane.

(43) 1 mg of organic dye dissolved in 1 mL of dichloromethane. Then made mixture of 2 g PDMS elastomer base (Sylgard 184) and PDMS curing agent (DC184A, weight ratio=10:1). After gentle shaking for 5 mins, the mixture was poured into a plastic petridish (2 cm×4.5 cm; diameter: 0.5 cm) and cured at 70° C. for 2 h to get a colorless film (thickness: 2.5 mm). The thickness of the film can be controlled by choosing a proper size of the dish.On top of the PDMS polymer wrote three letters N C L by using capillary tube for understanding change in colour of letters after exposure of NIR light (980 nm). The letter N belongs to NaYF.sub.4: Yb.sup.3+, Er.sup.3+, letter C belongs to organic dye and letter L belongs to NaYF.sub.4: Yb.sup.3+, Tm.sup.3+.

ADVANTAGES OF THE INVENTION

(44) a) Microrods for making a security tags. b) Surface functionalization with different dyes are possible for an efficient energy transfer purpose that could be useful for sensing application due to high efficient up-conversion process with microrods.