Patent Description:
Luminescence can be classified into multiple types such as photoluminescence, electroluminescence, cathodoluminescence, radioactive luminescence, chemiluminescence and bioluminescence, wherein photoluminescence can be classified into conventional photoluminescence [hereinafter referred to as conventional luminescence] and upconversion luminescence. The wavelength of incident excitation light of the conventional luminescence is less than the wavelength of emission light, and its characteristics are that luminescence efficiency is high and the quantum efficiency can reach or even exceed <NUM>%. Relative to conventional luminescence, upconversion luminescence can convert infrared light into ultraviolet or visible light. Its unique luminescence characteristics can be applied to the fields of biomedicine, solar cells, infrared anti-counterfeiting and laser display. Thus, upconversion luminescence is widely concerned. The upconversion luminescence needs an activator or an energy transfer process between the activator and a sensitizer, which requires the intermediate level of luminescent ions to have a long life. At present, there are not many kinds of elements that can achieve upconversion luminescence at room temperature, most of which are lanthanides. Compared with other lanthanides, Yb ion has a large absorption cross section (<NUM>× <NUM>-<NUM> cm<NUM>) and a simple energy level structure, and is easy to achieve high concentration doping. When <NUM> infrared light is used as the excitation source, Yb ion as a sensitizer can significantly enhance the upconversion luminescence of the material [(<NUM>) <NPL>]. Since the wavelength of the incident excited light of upconversion luminescence is larger than the wavelength of the emitted light, it is difficult to achieve high luminescence efficiency. Up to now, the maximum quantum efficiency of the upconversion phospher is still not up to <NUM>%, and most of the maximum quantum efficiency is only <NUM>% or lower.

In order to further increase the luminescence efficiency of the upconversion phospher, in addition to selecting luminescent ions with high efficiency emission levels, sensitized ions and appropriate excitation channels, it is also necessary to reduce the probability of non-radiative transition of the material. The selection of appropriate substrate materials is another most direct method for increasing the upconversion luminescence efficiency. The selection of substrate lattices not only determines the relative spatial positions between doped ions, but also affects the type and coordination number of anions around the doped ions. The interaction between the substrate lattices and the doped ions has great influences on the upconversion luminescence characteristics and luminescence efficiency of the materials. There are two main criteria for the selection of the substrate materials: (<NUM>) the selection of the substrate materials with low phonon energy can reduce the multi-phonon non-radiative relaxation, extend the lifetime of excited states, and increase the upconversion luminescence efficiency; (<NUM>) if the substrate materials with low crystal structure symmetry are selected, the f-f electric dipole transition of the upconversion luminescence is forbidden according to the parity selection rule of the lanthanide electron transition. However, in the substrate with low crystal symmetry, the electric dipole transition of the 4fn configuration is possible due to the odd order term of the crystal field, thereby improving the upconversion luminescence and luminescence efficiency.

According to the above criteria, the substrate materials with high upconversion luminescence efficiency are screened:.

Sulfide is an excellent conventional phosphor substrate, and has been widely used in the fields of photoluminescence, electroluminescence, cathodoluminescence and radioactive luminescence. Transition metal sulfides such as ZnS:Cu and ZnS:Ag are excellent conventional materials of photoluminescence, electroluminescence, cathodoluminescence and radioactive luminescence. Alkaline earth metal sulfides such as CaS can be used in long afterglow materials [(<NUM>) <CIT>] and electron trapping materials [(<NUM>) <CIT>]. Rare earth sulfide is an excellent high-grade pigment, and thus is difficult to apply to luminescence [(<NUM>) <NPL>]. Alkaline earth ternary sulfide has a suitable band gap, is an excellent conventional luminescent substrate material, and can be used in the field of LED lighting lamps [(<NUM>) <CIT>. (<NUM>) <CIT>. (<NUM>) <CIT>. (<NUM>) <NPL>. (<NUM>) <NPL>. (<NUM>) <NPL>. (<NUM>) <NPL>. (<NUM>) <NPL>. (<NUM>) <NPL>. (<NUM>) <NPL>. (<NUM>) <NPL>. ], fiber optic amplifier [(<NUM>) <CIT>], electroluminescence [(<NUM>) <NPL>. (<NUM>) <NPL>] or laser [(<NUM>) <NPL>. (<NUM>) <NPL>].

The rare earth polysulfide has low phonon energy equivalent to the chloride, and has good chemical stability. For example, the highest phonon energy of NaYS<NUM> is <NUM>-<NUM>, which is lower than the phonon energy of β-NaYF<NUM>(<NUM>-<NUM>) with the highest upconversion luminescence efficiency at present. NaYS<NUM> belongs to the low symmetry crystal system, and conforms to the conditions of serving as an ideal upconversion substrate material. The upconversion luminescence material that takes NaYS<NUM> as the substrate should have higher upconversion luminescence efficiency. The rare earth sulfide has been used for the high-grade pigment for a long time and is often sensitized by Yb ions. However, there are very few reports on the upconversion luminescence of sulfide substrates.

Higuchi et al. reported the upconversion luminescence of Er<NUM>+ ions in Ga<NUM>S<NUM>-Ges<NUM>-La<NUM>S<NUM> glasses at <NUM> and <NUM> excitation at first, but its green upconversion luminescence quantum efficiency is less than half of fluoride glass [(<NUM>) <NPL>]. In addition, the research of Pascal et al. showed that in pure sulfides, the LMCT absorption edge of S<NUM>-→Yb<NUM>+ is less than <NUM>-<NUM> and overlaps with the <NUM>H<NUM>/<NUM>, <NUM>S<NUM>/<NUM> and <NUM>F<NUM>/<NUM> energy levels of Er<NUM>+. The luminescence intensity of the upconversion luminescence phospher of NaYS<NUM> excited by <NUM> and co-doped by Yb<NUM>+ and Er<NUM>+ is decreased by two orders of magnitude. Therefore, it is generally accepted that the pure rare earth sulfide is not an effective substrate material for the traditional Yb<NUM>+ sensitized upconversion luminescence [(<NUM>) <NPL>. (<NUM>) <NPL>].

In view of the above defects of the prior art, the present invention provides a polysulfide upconversion phosphor according to claim <NUM> and <NUM> with high luminescence efficiency, which realizes upconversion luminescence of three primary colors of red, green and blue, and upconversion luminescence of ultraviolet and near-infrared light through multi-wavelength excitation. The phosphor has the advantages of high upconversion luminescence brightness, stable chemical properties and good biocompatibility.

The present invention has the following technical solution:.

The phosphor can emit ultraviolet, blue, blue-green, green, red and near-infrared light when excited by near infrared light at <NUM>-<NUM>.

In the upconversion phosphor with general formula of composition of mA<NUM>S·nBS·kC<NUM>-xS<NUM>:Dx, when D contains Er, a preferred x value is <NUM>-<NUM>; the ranges of excitation wavelengths are <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>; and the three excitation wavelengths can be used separately or simultaneously.

In the upconversion phosphor with general formula of composition of mA<NUM>S·nBS·kC<NUM>-xS<NUM>:Dx, when D contains Ho, a preferred x value is <NUM>-<NUM> and the used range of excitation wavelengths is <NUM>-<NUM>.

In the upconversion phosphor with general formula of composition of mA<NUM>S·nBS·kC<NUM>-xS<NUM>:Dx, when D contains Tm, a preferred x value is <NUM>-<NUM>; the used ranges of excitation wavelengths are <NUM>-<NUM> and <NUM>-<NUM>; and the two excitation wavelengths can be used separately or simultaneously.

The present invention has the following beneficial effects:
The polysulfide with mA<NUM>S·nBS·kC<NUM>-xS<NUM>:Dx as a general chemical formula has very low phonon energy, belongs to a low-symmetry crystal system, and is an ideal upconversion phosphor substrate. Under the condition of preferably selecting the appropriate concentration of ion doping, because the distance between doped ions is far greater than that of conventional phosphor, high-concentration doping and the reduction of radiation-free relaxation can be achieved. The upconversion luminescence efficiency is higher than that of conventional NaYF<NUM>:Yb, Er, and multi-wavelength excitation can be achieved at the same time. Especially, infrared light in the range of <NUM>-<NUM> has a safe wavelength for human eyes. When the light source of this band is used as an excitation source, the present invention can also reduce the protection level of application scenarios or does not use protective equipment to extend the application range, and the brightness is the highest, which is particularly beneficial to the application.

Different compositions and luminescence properties of the polysulfide of the present invention are described below through specific embodiments.

Reference embodiment <NUM>: green upconversion phosphor of commercial β-NaYF<NUM>:Yb,Er.

Reference embodiment <NUM>: blue upconversion phosphor of commercial β-NaYF<NUM>:Yb,Tm.

Reference embodiment <NUM>: red upconversion phosphor of commercial Y<NUM>O<NUM>:Yb,Er.

The sample of the present invention is prepared by a solid phase reaction method, and raw materials are weighed according to the molar ratio of the constituent elements. The raw materials may be oxides, carbonates, oxalates, nitrates, acetate and sulfates of the elements mentioned in the technical solution. The raw materials are porphyrized and mixed evenly by a dry mixing method, put into a crucible, placed in a high temperature furnace, and calcined in a vulcanization atmosphere (such as H<NUM>S and CS<NUM>) at <NUM>-<NUM> for <NUM>-<NUM>. The calcination time is adjusted according to the amount of the materials. To improve the brightness, a small amount of cosolvent, such as <NUM>-<NUM> wt% of AF and/or BF<NUM>, including NH<NUM>Cl, NH<NUM>F, MgF<NUM>, CaF<NUM>, SrF<NUM> and BaF<NUM>, can be added to the raw materials, which can significantly improve the upconversion luminescence efficiency.

The present invention measures the luminescence brightness or luminescence intensity of the sample to evaluate the luminescence efficiency. The specific measurement method of the luminescence brightness comprises: placing the sample in a black disk with a diameter of <NUM> and a depth of <NUM>, and flattening the sample with a glass sheet to eliminate the influence caused by scattering. An excitation light source is a semiconductor laser. For visible light samples, after the sample is irradiated by a laser, the brightness of the sample is measured by a brightness meter. Commercial β-NaYF<NUM>:Yb,Er (green), β-NaYF<NUM>:Yb,Tm (blue) and Y<NUM>O<NUM>:Yb,Er (red), which have the highest upconversion luminescence efficiency at present, are used as reference samples. For invisible samples, compared with a method for measuring the luminescence intensity by a spectrometer, all test conditions are consistent in a set of embodiments.

Embodiment <NUM>: Y<NUM>O<NUM> (<NUM>%) and Er<NUM>O<NUM> (<NUM>%) are used as initial raw materials. The raw materials are weighed according to a chemical formula ratio Y<NUM>S<NUM>: Er<NUM>, fully ground for <NUM> minutes, and placed in a quartz tube; and then the quartz tube is placed in a resistance furnace. CS<NUM> bubbles are introduced by Ar gas, or H<NUM>S gas containing Ar carrier gas is directly used; then, the sample is heated to <NUM> at a speed of <NUM>/min, preserved at the temperature for <NUM> hours and cooled to room temperature; and the sample is ground to obtain a target product. A <NUM> laser is used as the excitation source and compared with reference embodiment <NUM>. The performance indexes are shown in the following table.

Embodiment <NUM> to embodiment <NUM> can be obtained by the similar methods.

Embodiments <NUM>-<NUM> are comparative examples and do not fall within the scope of the claims.

The influences of other parameters not listed in embodiments <NUM>-<NUM> on luminescence colors, luminescence intensity and thermal properties can also be obtained by the methods similar to those of embodiments <NUM>-<NUM>. When A=Rb or Cs, there is a similar result as A=K, but Rb and Cs are more expensive. When A is used in combination, the performance is better. The combination of A=Li and K can make the particle size of the product more uniform. Under the condition of keeping the luminescence intensity unchanged, the reaction temperature can be appropriately reduced by <NUM>-<NUM>. When B=Be, Ba, or Cd, there are similar results as B=Ca, but considering the environmental protection requirements, products containing these elements may encounter difficulties when applied. When B=Zn, the flow rate and the reducibility of a carrier gas atmosphere should be controlled. When C=Al, Ga or Bi, it is usually used for replacing no more than <NUM>% of La, Gd, Lu, Y or Sc, which can improve the luminescence intensity by about <NUM>-<NUM>%. When D=Er, the used ranges of the excitation wavelengths are <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM>. The three excitation wavelengths can be used separately or simultaneously, and the effect is similar to that of the <NUM> excitation light source. The selection of the wavelengths of the excitation light source depends on the application conditions and the laser wavelengths available in bulk on the market. For luminescence brightness, infrared light in the wavelength range of <NUM>-<NUM> is used > infrared light in the wavelength range of <NUM>-<NUM> is used > infrared light in the wavelength range of <NUM>-<NUM> is used. Especially, infrared light in the range of <NUM>-<NUM> has a safe wavelength for human eyes and has the highest brightness, which is particularly advantageous for application. In the above embodiment, a small amount of cosolvent is added to the raw materials, such as <NUM>-<NUM> wt% of NH<NUM>Cl, NH<NUM>F, MgF<NUM>, CaF<NUM>, SrF<NUM>, BaF<NUM>, etc., which can further improve the luminescence brightness by <NUM>-<NUM>%. The combined use realizes better performance.

When RE=Er, the physical properties of the material can also be changed through combination and co-doping with other RE ions, such as luminescence colors and endothermic performance. If a small amount of (x=<NUM>-<NUM>) Mo and W is added, the red luminescence component in the luminescence spectrum can be significantly reduced, and the color purity of green luminescence can be increased by <NUM>-<NUM> times. If Ho, Tm or Pr is added, the red luminescence component in the luminescence spectrum can be increased; the color purity of red luminescence can be increased by <NUM>-<NUM> times; and the luminescence brightness is <NUM>-<NUM>% of that of reference embodiment <NUM> under the same excitation condition. At the same time the color purity of red luminescence is <NUM>-<NUM>% of that of reference embodiment <NUM>. If Yb, Ce, Sm, Tb, Eu or Nd is added, the thermal properties can be significantly enhanced and the luminescence colors can be changed; and at the same power density, the temperature rise of the sample can be more than doubled.

When RE=Ho, the excitation wavelength can be changed to <NUM>-<NUM>, and the color purity of the green luminescence is more than <NUM>% higher than that of RE=Er. When RE=Tm, the excitation wavelength can be changed to <NUM>-<NUM> and <NUM>-<NUM>, and the brightness of green luminescence is <NUM>-<NUM>% of that of reference embodiment <NUM> under the same excitation conditions, thereby widening the application range. Through further combination with other RE, panchromatic luminescence can be obtained, or the color purity can be adjusted.

When the values of m, n, k and x are beyond the range of embodiments <NUM>-<NUM>, such as m=<NUM>-<NUM>, n=<NUM>-<NUM>, k=<NUM>-<NUM>, k=<NUM>-<NUM> and x=<NUM>-<NUM>, the sample also has a good luminescence effect, but the luminescence intensity is reduced by <NUM>-<NUM>% compared with embodiments <NUM>-<NUM> under the same conditions.

Y<NUM>O<NUM> (<NUM>%), Er<NUM>O<NUM> (<NUM>%) and Na<NUM>CO<NUM>(<NUM>-<NUM>%) are used as initial raw materials. The raw materials are weighed according to a chemical formula ratio NaY<NUM>S<NUM>: Er<NUM>, fully ground for <NUM> minutes, and placed in a quartz tube; and then the quartz tube is placed in a resistance furnace. CS<NUM> bubbles are introduced by Ar gas; then, the sample is heated to <NUM> at a speed of <NUM>/min, preserved at the temperature for <NUM> hours and cooled to room temperature; and the sample is ground to obtain a target product.

<FIG> shows the upconversion luminescence spectrum of NaY<NUM>S<NUM>: Er<NUM> sample under <NUM> excitation. It can be seen that the NaY<NUM>S<NUM>: Er<NUM> sample shows green emission at <NUM>-<NUM> band and red emission at <NUM>-<NUM>, corresponding to Er<NUM>+ transitions at energy levels <NUM>S<NUM>/<NUM>→<NUM>I<NUM>/<NUM>, <NUM>H<NUM>/<NUM>→<NUM>I<NUM>/<NUM> and <NUM>F<NUM>/<NUM>→<NUM>I<NUM>/<NUM>, respectively.

To further evaluate the upconversion luminescence performance of NaY<NUM>S<NUM>: Er<NUM>, the luminescence brightness data of the NaY<NUM>S<NUM>: Er<NUM> samples under the <NUM> and <NUM> excitation of the same power are compared with reference embodiment <NUM> (<FIG>). Under <NUM> excitation, NaY<NUM>S<NUM>: Er<NUM> has very high upconversion luminescence efficiency, and the brightness is -<NUM> times that of <NUM> excitation, and even more than twice that of commercial NaYF<NUM>:Yb, Er under <NUM> excitation.

The influences of other parameters not listed in embodiments <NUM>-<NUM> on luminescence colors, luminescence intensity and thermal properties can also be obtained by the methods similar to those of embodiments <NUM>-<NUM>. The effects are similar to the example listed below in embodiments <NUM>-<NUM>, but the luminescence intensity is higher than that listed below in embodiments <NUM>-<NUM> by <NUM>-<NUM>%.

Embodiment <NUM> to embodiment <NUM> can be obtained by the similar methods to embodiments <NUM>-<NUM>.

The influences of other parameters not listed in embodiments <NUM>-<NUM> on luminescence colors, luminescence intensity and thermal properties can also be obtained by the methods similar to those of embodiments <NUM>-<NUM>. The effects are similar to the example listed below in embodiments <NUM>-<NUM>.

Y<NUM>O<NUM> (<NUM>%) and Er<NUM>O<NUM> (<NUM>%) of a certain mass are weighed according to the stoichiometric ratio of NaY<NUM>S<NUM>: Er<NUM> and stirred with appropriate amount of water and <NUM> mol/L hydrochloric acid to form rare earth chloride. An appropriate amount of oleic acid and octadecene are taken; and a certain amount of sulfur powder and sodium oleate are weighed, and mixed with the above rare earth chloride. The water and other low boiling point impurities are removed under vacuum environment at <NUM>. Then, the solution is rapidly heated to <NUM> and kept at the temperature for <NUM> hour. The sample is washed with water and ethanol and dried for many times to obtain the NaY<NUM>S<NUM>: Er<NUM> sample. Y<NUM>O<NUM> (<NUM>%), Yb<NUM>O<NUM> (<NUM>%) and Er<NUM>O<NUM> (<NUM>%) are weighed to prepare the rare earth chlorides. The above steps are repeated and the prepared NaY<NUM>S<NUM>: Er<NUM> is added into the mixture and kept at <NUM> for <NUM> hour to form a core-shell structure Na Y<NUM>S<NUM>: Er<NUM>@NaY<NUM>S<NUM>:Yb<NUM>, Er<NUM> sample.

<FIG> shows the upconversion luminescence spectrum of NaY<NUM>S<NUM>: Er<NUM>@NaY<NUM>S<NUM>:Yb<NUM>, Er<NUM> sample under <NUM> excitation. The spectrum is formed by two groups of bands in the visible part. Green emission at <NUM>-<NUM> band and red emission at <NUM>-<NUM> correspond to transitions of Er<NUM>+ ions at <NUM>S<NUM>/<NUM>→<NUM>I<NUM>/<NUM>, <NUM>H<NUM>/<NUM>→<NUM>I<NUM>/<NUM> and <NUM>F<NUM>/<NUM>→<NUM>I<NUM>/<NUM>, respectively. Compared with the NaY<NUM>S<NUM>: Er<NUM> sample, NaY<NUM>S<NUM>: Er<NUM>@NaY<NUM>S<NUM>:Yb<NUM>, Er<NUM> is similar in peak pattern, but the relative emission intensity of red and green light bands is quite different. NaY<NUM>S<NUM>: Er<NUM> shows strong green light and weak red light, and NaY<NUM>S<NUM>: Er<NUM>@NaY<NUM>S<NUM>:Yb<NUM> and Er<NUM> shows strong red light and weak green light. Under the same excitation conditions, the pyrogenetic capacity of the sample is <NUM> times that of embodiment <NUM>, and thus the sample can be used in occasions where both light and thermal effects are required.

Y<NUM>O<NUM> (<NUM>%) and Er<NUM>O<NUM> (<NUM>%) of a certain mass are weighed according to the stoichiometric ratio of NaGd<NUM>S<NUM>: Er<NUM> and stirred with appropriate amount of water and <NUM> mol/L hydrochloric acid to form rare earth chloride. An appropriate amount of oleic acid and octadecene are taken; and a certain amount of sulfur powder and sodium oleate are weighed, and mixed with the above rare earth chloride. The water and other low boiling point impurities are removed under vacuum environment at <NUM>. Then, the solution is rapidly heated to <NUM> and kept at the temperature for <NUM> hour. The sample is washed with water and ethanol and dried for many times to obtain the NaGd<NUM>S<NUM>: Er<NUM> sample. Y<NUM>O<NUM> (<NUM>%), Er<NUM>O<NUM> (<NUM>%) and Ho<NUM>O<NUM> (<NUM>%) are weighed to prepare the rare earth chlorides. The above steps are repeated and the prepared NaY<NUM>S<NUM>: Er<NUM> is added into the mixture and kept at <NUM> for <NUM> hour to form a core-shell structure NaGd<NUM>S<NUM>: Er<NUM>@NaGd<NUM>S<NUM>:Er<NUM>, Ho<NUM> sample.

<FIG> shows the emission spectrum of NaGd<NUM>S<NUM>: Er<NUM>@NaGd<NUM>S<NUM>:Er<NUM>, Ho<NUM> sample under <NUM> laser excitation. The emission spectrum in <FIG> is formed by two groups of bands: <NUM>) The red luminescence band located at band of <NUM>-<NUM>: there are three emission peaks, located at <NUM>, <NUM> and <NUM> respectively, corresponding to the <NUM>F<NUM> → <NUM>I<NUM> transition of Ho<NUM>+ ions. <NUM>) The green luminescence band located at band of <NUM>-<NUM>: there are two emission peaks, located at <NUM> and <NUM> respectively, corresponding to the <NUM>F<NUM> → <NUM>I<NUM> and <NUM>S<NUM> → <NUM>I<NUM> transitions of Ho<NUM>+ ions.

Y<NUM>O<NUM> (<NUM>%), Er<NUM>O<NUM> (<NUM>%) and Nd<NUM>O<NUM> (<NUM>%) of a certain mass are weighed according to the stoichiometric ratio of NaY<NUM>S<NUM>:Er<NUM>, Nd<NUM> and stirred with appropriate amount of water and <NUM> mol/L hydrochloric acid to form rare earth chloride. An appropriate amount of oleic acid and octadecene are taken; and a certain amount of sulfur powder and sodium oleate are weighed, and mixed with the above rare earth chloride. The water and other low boiling point impurities are removed under vacuum environment at <NUM>. Then, the solution is rapidly heated to <NUM> and kept at the temperature for <NUM> hour. The sample is washed with water and ethanol and dried for many times to obtain the NaY<NUM>S<NUM>:Er<NUM>, Nd<NUM> sample. Y<NUM>O<NUM> (<NUM>%), Yb<NUM>O<NUM> (<NUM>%) and Tm<NUM>O<NUM> (<NUM>%) are weighed to prepare the rare earth chlorides. The above steps are repeated and the prepared NaY<NUM>S<NUM>:Er<NUM>, Nd<NUM> is added into the mixture and kept at <NUM> for <NUM> hour to form a core-shell structure NaY<NUM>S<NUM>:Er<NUM>, Nd<NUM>@NaY<NUM>S<NUM>: Yb<NUM>, Nd<NUM>, Tm<NUM> sample.

<FIG> shows the emission spectrum of NaY<NUM>S<NUM>:Er<NUM>, Nd<NUM>@NaY<NUM>S<NUM>: Yb<NUM>, Nd<NUM>, Tm<NUM> sample under <NUM> laser excitation. The spectrum in the figure is formed by three groups of bands: <NUM>) The blue luminescence band located at band of <NUM>-<NUM>, and the peak value is located at <NUM>, which belongs to the <NUM>G<NUM> → <NUM>H<NUM> transition of Tm<NUM>+; <NUM>) The red luminescence band located at band of <NUM>-<NUM>, and the peak value is located at <NUM>, which belongs to the <NUM>G<NUM> → <NUM>F<NUM> transition of Tm<NUM>+ ions; and <NUM>) the red luminescence band located at band of <NUM>-<NUM>, and the peak value is located at <NUM>, which belongs to the <NUM>F<NUM> → <NUM>H<NUM> transition of Tm<NUM>+ ions. The blue light emission band is significantly stronger than the two red light emission bands, so NaY<NUM>S<NUM>:Er<NUM>, Nd<NUM>@NaY<NUM>S<NUM>: Yb<NUM>, Nd<NUM>, Tm<NUM> samples show bright blue luminescence under observation by naked eyes.

Y<NUM>O<NUM> (<NUM>%) and Er<NUM>O<NUM> (<NUM>%) of a certain mass are weighed according to the stoichiometric ratio of NaY<NUM>S<NUM>: Er<NUM> and stirred with appropriate amount of water and <NUM> mol/L hydrochloric acid to form rare earth chloride. An appropriate amount of oleic acid and octadecene are taken; and a certain amount of sulfur powder and sodium oleate are weighed, and mixed with the above rare earth chloride. The water and other low boiling point impurities are removed under vacuum environment at <NUM>. Then, the solution is rapidly heated to <NUM> and kept at the temperature for <NUM> hour. The sample is washed with water and ethanol and dried for many times to obtain the NaY<NUM>S<NUM>:Er<NUM> sample. Y<NUM>O<NUM> (<NUM>%), Yb<NUM>O<NUM> (<NUM>%) and Nd<NUM>O<NUM> (<NUM>%) are weighed to prepare the rare earth chlorides. The above steps are repeated and the prepared NaY<NUM>S<NUM>:Er<NUM> is added into the mixture and kept at <NUM> for <NUM> hour to form a core-shell structure NaY<NUM>S<NUM>:Er<NUM>@NaY<NUM>S<NUM>: Yb<NUM>, Nd<NUM> sample.

The upconversion luminescence spectrum of the NaY<NUM>S<NUM>:Er<NUM>@NaY<NUM>S<NUM>: Yb<NUM>, Nd<NUM> sample is formed by three groups of bands: green emission located at the band of <NUM>-<NUM>, red emission at the band of <NUM>-<NUM> and infrared emission at the band of <NUM>-<NUM>, corresponding to <NUM>S<NUM>/<NUM>→<NUM>I<NUM>/<NUM>, <NUM>H<NUM>/<NUM>→<NUM>I<NUM>/<NUM> and <NUM>F<NUM>/<NUM>→<NUM>I<NUM>/<NUM> transitions of Er<NUM>+ ions and <NUM>F<NUM>/<NUM>/<NUM>F<NUM>/<NUM>/<NUM>F<NUM>/<NUM>→<NUM>I<NUM>/<NUM> transitions of Nd<NUM>+ ions, respectively. Compared with the NaY<NUM>S<NUM>: Er<NUM> sample, the pyrogenetic capacity of the NaY<NUM>S<NUM>:Er<NUM>@NaY<NUM>S<NUM>: Yb<NUM>, Nd<NUM> sample is significantly improved.

Y<NUM>O<NUM> (<NUM>%) and Er<NUM>O<NUM> (<NUM>%) of a certain mass are weighed according to the stoichiometric ratio of NaY<NUM>S<NUM>: Er<NUM> and stirred with appropriate amount of water and <NUM> mol/L hydrochloric acid to form rare earth chloride. An appropriate amount of oleic acid and octadecene are taken; and a certain amount of sulfur powder and sodium oleate are weighed, and mixed with the above rare earth chloride. The water and other low boiling point impurities are removed under vacuum environment at <NUM>. Then, the solution is rapidly heated to <NUM> and kept at the temperature for <NUM> hour. The sample is washed with water and ethanol and dried for many times to obtain the NaY<NUM>S<NUM>:Er<NUM> sample. Y<NUM>O<NUM> (<NUM>%),Yb<NUM>O<NUM> (<NUM>%) and Sm<NUM>O<NUM> (<NUM>%) are weighed to prepare the rare earth chlorides. The above steps are repeated and the prepared NaY<NUM>S<NUM>:Er<NUM> is added into the mixture and kept at <NUM> for <NUM> hour to form a core-shell structure NaY<NUM>S<NUM>:Er<NUM>@NaY<NUM>S<NUM>: Yb<NUM>, Sm<NUM> sample.

The upconversion luminescence spectrum of the NaY<NUM>S<NUM>:Er<NUM>@NaY<NUM>S<NUM>: Yb<NUM>, Sm<NUM> sample is formed by three groups of bands: green emission located at the band of <NUM>-<NUM> and red emission at the bands of <NUM>-<NUM> and <NUM>-<NUM>, corresponding to <NUM>G<NUM>/<NUM>→<NUM>H<NUM>/<NUM>, <NUM>G<NUM>/<NUM>→<NUM>H<NUM>/<NUM>, <NUM>G<NUM>/<NUM>→<NUM>H<NUM>/<NUM> transitions of Sm<NUM>+ ions, respectively. Compared with the NaY<NUM>S<NUM>: Er<NUM> sample, the NaY0.9S2:Er0. <NUM>@NaY0.9S2: Yb0. <NUM>, Sm0. <NUM> sample can generate much heat.

Y<NUM>O<NUM> (<NUM>%) and Er<NUM>O<NUM> (<NUM>%) of a certain mass are weighed according to the stoichiometric ratio of NaY<NUM>S<NUM>: Er<NUM> and stirred with appropriate amount of water and <NUM> mol/L hydrochloric acid to form rare earth chloride. An appropriate amount of oleic acid and octadecene are taken; and a certain amount of sulfur powder and sodium oleate are weighed, and mixed with the above rare earth chloride. The water and other low boiling point impurities are removed under vacuum environment at <NUM>. Then, the solution is rapidly heated to <NUM> and kept at the temperature for <NUM> hour. The sample is washed with water and ethanol and dried for many times to obtain the NaY<NUM>S<NUM>:Er<NUM> sample. Y<NUM>O<NUM> (<NUM>%), Yb<NUM>O<NUM> (<NUM>%) and Eu<NUM>O<NUM> (<NUM>%) are weighed to prepare the rare earth chlorides. The above steps are repeated and the prepared NaY<NUM>S<NUM>:Er<NUM> is added into the mixture and kept at <NUM> for <NUM> hour to form a core-shell structure NaY<NUM>S<NUM>:Er<NUM>@NaY<NUM>S<NUM>: Yb<NUM>, Eu<NUM> sample.

The upconversion luminescence spectrum of the NaY<NUM>S<NUM>:Er<NUM>@NaY<NUM>S<NUM>: Yb<NUM>, Eu<NUM> sample is formed by three groups of bands: green emission located at the band of <NUM>-<NUM> and red emission at the bands of <NUM>-<NUM> and <NUM>-<NUM>. Compared with the NaY<NUM>S<NUM>: Er<NUM> sample, the red luminescence of the NaY<NUM>S<NUM>:Er<NUM>@NaY<NUM>S<NUM>: Yb<NUM>, Eu<NUM> sample is significantly enhanced.

Claim 1:
The use of a polysulfide phosphor for upconversion luminescence, wherein a general formula of composition of the polysulfide phosphor is: mA<NUM>S·nBS·kC<NUM>-xS<NUM>:Dx; A is one or more than one of Li, Na, K, Rb and Cs, and B is one or more than one of Be, Mg, Ca, Sr, Ba, Zn and Cd; C is one or more than one of La, Gd, Lu, Y, Sc, Al, Ga and Bi; D is one or more than one of Ho, Er, Tm and Pr, optionally co-doped with Mo, W, Ce, Sm, Tb, Yb, Eu or Nd; x=<NUM>-<NUM>;
n=<NUM>-<NUM>, m = <NUM>-<NUM> and k =<NUM>-<NUM>;
m=<NUM>-<NUM>, n =<NUM>-<NUM>, and k = <NUM>-<NUM>; or
m=<NUM>-<NUM>, n = <NUM>-<NUM>, and k =<NUM>-<NUM>;
wherein when D contains Er, x value is <NUM>-<NUM>; the phosphor is excitable within an excitation wavelengths range of <NUM>-<NUM> and/or <NUM>-<NUM>;
wherein when D contains Ho, x value is <NUM>-<NUM> and the phosphor is excitable within an excitation wavelengths range of <NUM>-<NUM>;
wherein when D contains Tm, x value is <NUM>-<NUM>; the phosphor is excitable within an excitation wavelengths range of <NUM>-<NUM> and/or <NUM>-<NUM>.