Cooling with anti-stokes fluorescence

Abstract

A double or multi-layer apparatus or device for optical anti-Stokes cooling of object surfaces. The apparatus comprises at least one bottom layer, which is configured to respond in anti-Stokes fluorescence upon absorption of electromagnetic radiation and at least one top layer, which is overlaid on the bottom layer and configured to filter the electromagnetic radiation and transmit selected spectral band of the electromagnetic radiation to the bottom layer. The active cooling does not depend on the coherent nature of the radiation, which enables the usage of incoherent solar radiation as the active cooling input power source. The cooling technology of the invention is suitable for small and large scales and practically for any object with surface on which the layer substance can be applied or overlaid, e.g., roof, wall, car, ship, tent, clothing, etc.

Claims

1. Apparatus for optical cooling of objects and/or object surfaces, said apparatus comprising: at least one bottom layer, said bottom layer is configured to respond in anti- Stokes fluorescence upon absorption of electromagnetic radiation; and at least one top layer, said top layer is overlaid on said bottom layer and configured to filter said electromagnetic radiation and transmits selected spectral band of said electromagnetic radiation to said bottom layer; wherein said electromagnetic radiation is incoherent non-monochromatic radiation with wide spectral band, wherein said selected spectral band is sufficient for excitation of electrons from ground energy state to excited energy state in active component in said bottom layer.

2. The apparatus according to claim 1, wherein said active component comprises at least one material selected from the group consisting of RE-ion doped materials, and crystalline semiconductor materials.

3. The apparatus according to claim 2, wherein said RE-ion is selected from Ytterbium in Ytterbium-doped yttrium lithium fluoride (Yb:YLF) crystal, Ytterbium in Ytterbium-doped tungstate crystal (Yb:KGW), 1 wt % Yb.sup.3+ in fluorozirconate glass (ZBLANP) doped with Yb.sup.3+, 9Be.sup.+ and Cesium.

4. The apparatus according to claim 2, wherein said semiconductor crystal or crystalline material is selected from CdS (Cadmium Sulfide), CdSe/ZnS, GaAs (Gallium Arsenide) and AlGaAs (Aluminum Gallium Arsenide).

5. The apparatus according to claim 4, wherein said CdS is provided as nano-belts, said nano-belts forming said bottom layer.

6. The apparatus according to claim 4, wherein said CdSe/ZnS is provided as Quantum Dots (QDs), said QDs forming said bottom layer.

7. The apparatus according to claim 1, wherein said at least one top layer is selected from Water, Aluminum Hydroxide, Calcium Carbonate, Titanium Dioxide, Zinc Oxide, Silica, Quartz, Chlorothalonil, Polysiloxanes, Nepheline Syenite, Titanium Dioxide, Silane, Methyl Ttri(ethylmethyl ketoxime), Octamethylcyclotetrasiloxane, Amorphous Silica, organic pigments, inorganic pigments, ceramic pigments, iron oxide, oxides, ceramic microspheres, propylene glycol, amorphous silica, naphta (hydrodesulfurized heavy petroleum), xylene, calcium carbonate, hydrocarbons, cyclo-alkanes and ethanol.

8. The apparatus according to claim 1, wherein said at least one bottom layer and at least top layer are provided in paint form.

9. The apparatus according to claim 1, wherein said apparatus is in the form of a double layer fiber, said at least one top layer is a shell of said fiber, said at least one bottom layer is core of said fiber.

10. The apparatus according to claim 9, wherein said double layer fiber is a textile fiber, said textile fiber is configured for making textiles for cooling covers and shields for objects and bodies.

11. The apparatus according to claim 10, wherein said covers and shields are selected from clothing, drapes, shades, curtains, bags, camping gear and food cooler covers.

12. The apparatus according to claim 1, wherein said object or object surface is selected from roof, wall, window, human body and food container.

13. The apparatus according to claim 1, wherein deposition of said at least one bottom layer at least one top layer is done on a substrate selected from thin Si, SOI substrate, wafer based Si or Ge substrate or Si or Ge epitaxial layers, wafer based on III-V group materials, wafers based on epitaxial layers of group III-V materials, wherein said Si and SOI Wafers are fabricated with low or high thermal and electrical resistance.

14. The apparatus according to claim 13, wherein said substrate is removable with chemical and/or mechanical process.

15. The apparatus according to claim 13, wherein said deposition is done on wafer, die level, a sample which contains array of devices or a single device level.

16. The apparatus according to claim 13, wherein said at least one top layer is deposited, processed and mounted, glued, coated, evaporated on, deposited or mechanically or chemically attached above said bottom active cooling layer.

17. The apparatus according to claim 13, wherein said deposition is selected from Chemical Vapor Deposition (CVD) including in low (LPCVD) and high (HPCVD) pressure, electrodeposition, Physical Vapor Deposition (PVD), casting deposition, thermal oxidation, epitaxial growth and thermal oxidation.

18. The apparatus according to claim 1, wherein said apparatus is fabricated with a buffer layer between said at least one bottom layer and said at least one top layer.

19. The apparatus according to claim 1 , wherein said apparatus is fabricated with a passivation layer, said passivation layer covering said apparatus or said at least one top layer, said passivation layer is configured to protect said top and or bottom layers layer physical, mechanical and electrical properties from physical, chemical or electrical damage, minimize its degradation over time and thermally and electrically isolate said bottom layers from environmental impacts.

20. The apparatus according to claim 1, wherein said apparatus is fabricated with a passivation layer, said passivation layer is deposited between said top layer and said at least one bottom layer, said passivation layer is configured to protect said top and or bottom layers layer physical, mechanical and electrical properties from physical, chemical or electrical damage, minimize its degradation over time and thermally and electrically isolate said bottom layers from environmental impacts.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1(a) shows the 4-level model for optical refrigeration.

(2) FIG. 1(b) shows an example of the 4-level model for optical refrigeration.

(3) FIG. 2 shows the semiconductor model for optical refrigeration.

(4) FIG. 3 shows a plot of calculated temperature change with optical cooling.

(5) FIG. 4 shows a plot of temperature change curves for ytterbium-doped ZBLAN.

(6) FIG. 5 schematically illustrates cooling effect obtained with a double layer paint of the present invention.

(7) FIG. 6 schematically illustrates cooling effect obtained with a double layered fiber (core & shell) of the present invention.

(8) FIG. 7 shows thee spectrum of the sun, which is modeled as a black body with a temperature of 5778K (shown in the solid line) with and without the atmospheric absorption.

(9) FIG. 8 shows the experimental system of the temperature measurement with IR camera.

(10) FIG. 9 shows the spectrometer experimental system.

(11) FIG. 10 shows the experimental results with the temperature as a function of the ZBLAN glass and the entire frame.

(12) FIG. 11 shows a graph with extracted experimental results from FIG. 10 with the average temperature normalized by the entire frame with filtered sunlight reaching from the 4000 second.

(13) FIG. 12 shows the experimental results of the intensity of filtered sunlight from reference glass and ZBLN.

(14) FIG. 13 shows the experimental results of the intensity normalized wavelength by sunlight simulator (upper curve) and trough the corresponding filter (lower curve).

(15) FIG. 14 shows the experimental results of the normalized intensities of ZBLN (upper curve) and differences from reference glass (lower curve).

(16) FIG. 15 experimental results intensity by wavelength of radiation of ZBLN of the difference between ZBLN and reference glass samples demonstrating the anti-Stokes scattering by ZBLN sample.

(17) FIG. 16 shows exponential decay of the temperature with time of a glass in air after closing the shutter.

DETAILED DESCRIPTION OF THE DRAWINGS

(18) As explained above, FIG. 1(a) (reproduced from Nemova G., Laser Cooling of Solids, p. 4, FIGS. 1(a)-(b)), shows the 4-level model for optical refrigeration for RE-doped glass, for example Yb.sup.3+:ZBLANP. Although the diagram initially relates to laser cooling, it is equally relevant to wide band radiation. A particular calculation for the 4-level model is shown in FIG. 1(b) (units in cm.sup.−1).

(19) Optical cooling in semiconductors is schematically illustrated in FIG. 2 and has been discussed earlier in the present application. The up-conversion of the excited photons resulting from thermal equilibrium between neighbor excited energy levels leads to photon emission with energy higher than that of the photon absorbed. Thus the optical cooling effect in semiconductor materials is achieved by phonons absorption and conversion of thermal energy to electromagnetic energy.

(20) FIG. 3 (reproduced from, Jun Zhang, Dehui Li, Renjie Chen, Qihua Xiong, Laser Cooling of a Semiconductor by 40 Kelvin: An Optical Refrigerator Based on Cadmium Sulfide Nanoribbons, Proc. of SPIE Vol. 8638) is an example plot of measured maximum ΔT (squares) and theoretically calculated temperature change curve (solid line) normalized to the pump power in K/mW for different pump wavelengths at 290K. The solid region corresponds to the cooling zone for Cadmium Sulfide engineered material. A drop of temperature resulting from absorption of photons with wavelengths between 505 nm and 560 nm can clearly be seen. Applying to wide band radiation as in the present invention, using a ˜505 nm-˜560 nm spectral band extracted from the solar radiation on Cadmium Sulfide would generate anti-stokes fluorescence resulting in effective cooling.

(21) FIG. 4 (reproduced from Anton Rayner, B.Sc. (Hons), Laser Cooling of Solids, Effect of Quantum efficiency and sample length, A thesis submitted to the University of Queensland for the Degree of Doctor of Philosophy, Department of Physics, January 2002) is another example plot of measured maximum AT and theoretically calculated temperature change curve for ytterbium-doped ZBLAN. A drop of temperature resulting from absorption of photons with wavelengths between 995 nm and 1100 nm is clearly observed. These two examples in FIGS. 3 and 4 are also valid for the case of optical cooling with wide band radiation as in the present invention.

(22) FIG. 5 schematically illustrates a particular configuration of a double layer of the present invention for generating optical cooling effect in an object (6). In this example, the two layers are provided as paint for coating the surface of the object (6) to be cooled. The bottom layer (1) is the active cooling layer that absorbs a selected spectral band of the solar radiation (5) under exposed conditions of the object (6) to the sun (4). The active layer (1) responds in anti-Stokes fluorescence (3), namely electromagnetic radiation with mean energy higher than the energy of the solar radiation that is absorbed. Cooling of the object (6) by the conversion of heat to electromagnetic radiation follows. The top layer or roof coating (2) filters the solar radiation (5) by reflecting part of it back into the atmosphere and allowing the appropriate spectral band to pass to the bottom active layer (1), where this spectral band is suitable for generating anti-Stokes fluorescence in the bottom layer (1) and optical cooling of the object (6).

(23) As described above, the double layer of the invention may be implemented in different configurations and for different uses.

(24) FIG. 6 schematically illustrates one particular implementation of the double layer structure of the invention in a double layer fiber (10). The shell (8) of the fiber (10) is the top layer that filters the incoming radiation to the desired wavelength range as depicted in FIG. 5. The core (7) of the fiber (10) is the bottom fluorescing layer that receives and absorbs the radiation in the filtered wavelength range and responds by emitting radiation in anti-Stokes fluorescence. The hollow inner space of the fiber (10) is sufficient to accommodate the core (7) as seen in the bottom (9) opening of the fiber core. FIG. 6 illustrates a structure of a fiber (10) that is suitable for any structure that comprises fibers and is used to cover an object that requires cooling or shield it from a heat source. In one particular example, the structure of the fiber (10) may be used in textiles for any use for cooling objects, bodies and spaces by covering them with the protective cooling textile or shielding them from a heat source. Particular applications of such covers and shields are selected from clothing, drapes, shades, curtains, bags, camping gear, food cooler covers and the like.

(25) The following description verifies experimentally the anti-Stokes active cooling modeling and invention presented in FIGS. 1-6, and demonstrate experimentally anti-Stokes active cooling mechanism which is induced by a solar radiation simulator on ZBLAN 1% Yb3+ sample. The experimental results are presented in FIGS. 8-16. In addition, the description exemplifies sample preparation of CdS active layer by fabrication and processing of chunks on Si substrate, which is considered a first step toward fabrication of active cooling layer of CdS nano-belts structure on Si substrate. In these experiments, the second layer is configured to filter incoming electromagnetic radiation and transmit selected spectral band of it to the bottom layer. The experimental results shown in FIGS. 8-16 display exemplary embodiments of the cooling layer of the present invention as schematically illustrated in FIGS. 1-6. These figures are for illustration and demonstration purposes and are not intended to be exhaustive or to limit the invention to the below description in any form.

(26) Experimental

(27) Temperature Measurements Using an IR Camera

(28) Experimental System

(29) The experimental system (100), shown in FIG. 8, was composed of a vacuum chamber (15) that contained a stand (16) with ceramic screws (for low heat conductance, not shown in the figure) that held a sample of the material or sample under test (10). The chamber had two windows (11) and (12) on its top side. Window (11) in FIG. 8 was made of regular glass (BK7), which is transparent to the near IR and the visible spectrum, so that the light (13) from the solar simulator could pass through to the sample. Various optical elements (14) were placed in between the sunlight simulator and the vacuum chamber, marked as “Optics” in FIG. 8. The main components were filter apparatuses, which were designed to block irrelevant parts of the solar spectrum and a lens that focused the light (13) from the simulator on the sample (10). Window (12) in FIG. 8 was made from ZnSe, which is a transparent material to the radiation of the IR camera. The IR camera (17) was directed at the sample through window (12).

(30) For the IR camera (17) we used Gobi-640-Gige-4782 with a thermal resolution of 0.05° C., an error of about 1° C. and sensitivity to wavelengths between 8-14 micrometers. The lens used in the IR camera (17) is a focusing lens with focal length of about 7 cm. The filters (14) we used allowed very high transmittance (>90%) in the 1000-1300 nm range for the first filter and 505-560 nm for the second filter and almost no transmittance in any other wavelength in the solar spectrum (>1%). The sunlight simulator (13) had a total power of 10 W.

(31) Experimental Procedures

(32) We started by testing the camera on objects that are known to be hotter/colder. Next, we tried to measure our Ytterbium-doped ZBLAN sample (notated as ZBLAN) with and without solar light, and see changes in the temperature. Based on the literature, we used the 1000-1030 nm filter for the ZBLAN. We also experimented with changing conditions including different angles of the camera and the samples, filtered and unfiltered light, with and without vacuum (vacuum of 60+−10 Torr), with and without the cover of the vacuum chamber, with and without a mirror below the ZBLAN sample (for light recirculation), with without an absorbing material in the vacuum chamber, with/without the windows of the vacuum chamber, with different lenses/no lens and with different glasses which are not expected to cool as reference samples.

(33) Results and Discussion

(34) When we used no filter the samples were always heated, as expected, due to Stokes scattering in the materials. The ZBLAN sample and the reference glasses samples showed no change in temperature with the 1000-1030 nm filter. We analyzed the data taken by the camera by taking the average of the glass's temperature and the average of the entire frame's temperature and then removing the effects that are apparent in the entire frame from the function of temperature of the glass. FIG. 10 (lower graph) shows the temperature as a function of time of the ZBLAN glass and the entire frame. We normalized and extracted the change in temperature of the ZBLAN sample, shown in FIG. 11.

(35) Experimenting the sample was first allowed to reach equilibrium with the shutter closed and then the temperature recording started at the 0 second mark with the shutter still closed. The shutter was then opened at the 4000 second mark. We can clearly see in both graphs that opening the shutter did not have an apparent effect on the sample. Equivalent results were obtained for many different conditions. In the next step, we improved and modified the experimental measurement setup (100), shown in FIG. 8, in order to realize an anti-Stokes scattering cooling effect.

(36) Using a Spectrometer to Detect Anti-Stokes Scattering

(37) Experimental System

(38) The modified experimental system (200), shown in FIG. 9, was very similar to (100) that used the IR camera, except for the replacement of its cover part (18) with a thick aluminum foil cover that blocked light however did not hold a vacuum condition in the chamber (15). The modified system also included the replacement of the IR camera (17), shown in FIG. 8 with a spectrometer (19) (Oceanview USB 2000+) with a resolution of less than 1 nm, as can be seen in FIG. 9.

(39) Experimental Procedures

(40) The first measurement was of the light from the solar simulator and then measurements of the ZBLAN and the reference glasses that were taken with simulated sunlight. Then, measurements with filtered light were taken for ZBLAN and reference glasses.

(41) Results and Discussion

(42) The experimental results shown in FIG. 12 are taken from the experiments with the spectrometer and the ZBLAN, which were used to estimate the cooling efficiency and equilibrium temperature of the ZBLAN. Using the filtered light of 1000-1030 nm, and the spectrometer, on the light reflected from a reference BK-7 glass and the ZBLAN we obtain the graph shown in FIG. 12.

(43) The graph shown in FIG. 12 clearly indicates that the ZBLAN shows enhanced emission of light below 1000 nm, an indication that anti-Stokes scattering has taken place in the sample, cooling it. In the next step we estimated the cooling efficiency.

(44) Cooling Efficiency Estimation

(45) The total cooling efficiency is the product of the various efficiencies in the system. The expected cooling power is equal to:
(Sunlight simulator power)×(transmission of filter)×(fraction of radiation that undergoes anti-Stokes scattering)×(cooling efficiency of anti-Stokes)×(Other losses of radiation power)

(46) The solar simulator power is 10 W. The filter transmits 0.21% of the total power of the sunlight simulator as shown in the graph of FIG. 13. In the upper curve in FIG. 13, we see the spectrum produced by the solar simulator. In lower curve we see the filtered spectrum.

(47) In order to calculate how much of the radiation is anti-Stokes scattered we took the difference of the Intensity function of the ZBLAN and the same function of the reference glass, as shown in the graph of FIG. 14. From this graph, we calculated that 6% of the impinging radiation is anti-Stokes scattered.

(48) In a further step, we normalized and extracted the change in temperature of the ZBLAN sample. To this end, we considered that the energy of a photon is proportional to its wavelength. Hence, using that relation, the peak wavelength after the filter, considered as the peak of the input wavelength, was 1014 nm and the peak wavelength after the anti-Stokes scattering, considered as the peak of the input wavelength, was 972.4 nm which is, as shown in FIG. 15. Thus, we obtain 1−972.4/1014=0.04=4% of efficiency from the total power of the radiation that undergoes anti-Stokes scattering.

(49) Other losses include light from the solar simulator that did not hit the lens, reflectance from filter, and more. We estimate those to be 0.5 of the total power. Giving P.sub.cooling=10 W×0.5 (light losses)×0.06 (no resonance)×0.002 (amplitude after band pass)×0.04 (efficiency)=0.27mW. We can plug this number and L=(1.1*1.5*0.3/4.86)=0.1 cm=10.sup.−3 m for our samples into the newton cooling equation, giving: ΔT=T0−0.03K+0.03K*e.sup.−bt, giving a final temperature of roughly 0.03° C., significantly below the uncertainty of the IR camera, and even below its thermal resolution. This required us to construct a system capable of temperature measurements with accuracy better than 1 mK.

(50) Using Diodes to Measure the ZBLAN Sample Temperature

(51) Experimental System

(52) The system is similar to the one using the IR camera shown in FIG. 8, however the window (12) was removed and replaced with a vacuum feedthrough which included the wiring of two diodes for temperature measurement (not shown in the figure). One diode was attached to the sample with vacuum grease (Apiezon H) and the other was used as reference. The diode temperature was read out using an SRS diode temperature monitor (SIM922A).

(53) Experimental Procedures

(54) Experiments were performed with both the ZBLAN sample, and a reference glass of the same dimensions. The samples were first allowed to reach thermal equilibrium, before being irradiated with light from the solar simulator. Both filtered and unfiltered light was used. Testes were also run with different illumination angles and vacuum conditions.

(55) Results and Discussion

(56) Most of the results showed very nice exponential temperature changes, as expected. All the samples tested showed heating when radiated with direct simulated sunlight or filtered light. After the shutter of the solar simulator was closed, all samples showed cooling back to ambient temperatures. The graph in FIG. 16 shows an exponential fit when the shutter was closed. The fit is the total change in temperature expected at infinite time (assuming exponential decay). b, is the b parameter in Newton's cooling equation, and is highly dependent on the material (in our fits we obtain values ranging from 0.006 to 0.0001. This range stems from differences in angle, location, and vacuum grease application procedures. The general model is presented in the following equation along with the values of its parameters and fit:

(57) $\frac{d\left(\Delta T\right)}{\mathrm{dt}}=-P_{\mathrm{cooling}}*\frac{1}{C}+b*\left(\Delta T\right)$$C=\frac{1}{b}*L*k=\left[\frac{W*s}{K}\right]$$\frac{\mathrm{Volume}}{\mathrm{Area}}=L=\mathrm{effective}\mathrm{length}k=\mathrm{constant}\mathrm{of}\mathrm{the}\mathrm{material}=\frac{1W}{K*m}\mathrm{for}\mathrm{glass}$$\Delta T=T_0-\frac{P_{\mathrm{cooling}}}{L*k}+\frac{P_{\mathrm{cooling}}}{L*k}*e^{-\mathrm{bt}}$

(58) In order to compare the heating of the ZBLAN to the heating of the reference glass we compared the total change in temperature expected by opening the shutter and irradiating the samples. The total expected temperature change was not the same even under the same conditions. This is expected since the location, angle, greasing etc. of the sample has some effect on the heating. However, the results for filtered light and direct light were significantly different, as well as the results for air or vacuum. We used all the measurements with similar conditions in vacuum with filtered sunlight for ZBLAN, and for the reference glass and performed a two-sample t test on the two groups. All of the fits had a chi-squared value of between 0.5 and 2.5 with an uncertainty (sigma) of 0.0015° C. The groups of total temperature change upon illumination are: ZBLAN—0.031, 0.08855, 0.171, 0.0999, 0.035° C. and reference glass: 0.218, 0.152, 0.29, 0.05° C. The means are 0.09° C. for the ZBLAN and 0.18 for the reference glass. The P-value calculated is 0.063, which is below the binary threshold usually used for statistical significance (0.05). Yet there were only 9 measurements made in these conditions, therefore more experiments are needed to determine whether the ZBLAN sample is heated less than the reference sample. Regardless of the reference glass, since we have shown that anti-Stokes scattering occurs in the ZBLAN sample, the heating is probably caused by environmental and geometrical effects in the sample, thus, a better experimental system may allow for cooling to be observed.

CONCLUSIONS

(59) Success Showing Anti-Stokes in Material Resulting in Cooling Effect

(60) We found that the Yb:ZBLAN sample is heated by the simulated solar light, but on average is heated less than a reference sample. Since we observed anti-Stokes scattering from the Yb:ZBLAN sample, we believe conclude that active cooling below the environment temperature is achieveable. We found that the ZBLAN sample on average is heated less than a reference sample, and the difference is very close to be statistically significant. In addition, we observed anti-Stokes scattering from the ZBLAN sample—which shows a cooling power equivalent to 0.03 mW. To verify statistically our findings in these experiments, we used all the measurements with similar conditions in vacuum with filtered sunlight for ZBLAN, and for the reference glass and performed a two-sample t test on the two groups. All of the fits had a chi-squared value of between 0.5 and 2.5 with an uncertainty (sigma) of 0.0015° C. The groups of total temperature change upon illumination are: ZBLAN—0.031, 0.08855, 0.171, 0.0999, 0.035° C. and reference glass: 0.218, 0.152, 0.29, and 0.05. The means are 0.09 for the ZBLAN and 0.18 for the reference glass. The P-value calculated is 0.063, which is below the binary threshold usually used for statistical significance (0.05).

(61) Yb:ZBLAN

(62) As detailed, some promising results were achieved using Yb:ZBLAN glass. This indicates that some amount of cooling may be expected if using this material. In addition, Yb:ZBLAN is relatively easy to produce at a large scale, and its cooling does not depend on a specific morphology.

(63) CdS

(64) It is contemplated within the scope of the present invention that CdS nano-belts may be cooled by anti-Stokes scattering. Hence we conclude that under certain conditions a layer comprising CdS nano-belts can also be used and function as an active cooling anti-stock layer.

(65) Recently, it was reported (Fontenot 2016) that successful cooling of CdSe/ZnS core shell quantum dots (QD) was accomplished using 647 nm laser radiation. Therefore, the other wavelengths may also be used for cooling different sized QDs. Additionally, the same authors demonstrated the successful incorporation of the aforementioned QDs into polymers.

(66) Since QDs are, in principle, significantly easier to produce than CdS nano-belts, and indeed, are produced in bulk by several companies, and since the polymerization process is rather straightforward and lends itself easily to upscaling, it is within the scope of the present invention to obtain anti-Stokes solar cooling with polymers into which various core-shell quantum dots are incorporated. Particular material, which is suitable for application as QD is CdSe/ZnS.

(67) Filter Top Layer and Bottom Layer Fabrication:

(68) Experiment demonstrated a ZBLAN test samples as an active cooling without the top filter layer, where the later filtering layer has been replaced with filtering devices which performed experimentally the similar functionalities of this layer. As discussed above, the present invention provides a double- or multi-layer structure that filters the radiation spectrum and transmits only a selected band to the layer that displays anti-Stokes fluorescence. Thus, the top layer shields the bottom layer from unnecessarily absorbed radiation and actually renders the cooling effect more efficient by increasing the ratio of radiation output-input. Such double- or multi-layer structure filters a radiation spectrum by reflecting most of it back and away by the outer layer and transmitting a selected band of it to a second layer. The second layer in the invention absorbs the selected part of the spectrum, shifts it to a shorter wavelength range using anti-Stokes effect and emits it in a radiative manner As a result, a cooling effect is obtained. Practically there are various methods to fabricate such double or multi-layer device comprising of active and filtering layers. Such fabrication method relates to the specific scale the size of the cooling systems and devices including its integration into the specific particular embodiments of the present invention. The deposition of the active layer can be done above thick or thin Si, SOI wafers (Si Over Insulator), wafers and substrate wafers based on Ge substrate or Epi wafer based on III-V materials such as GaAs wafers. Si and SOI Wafers can be fabricated with low or high thermal and electrical resistance. Generally, in several embodiments of this invention, the previous substrate layers can be removed in a chemical and a or mechanical process, such as a grinding process done on the wafer or die back side after completion of processing the active cooling device composed of two or multi layer devices. This process can be done on wafer, die level or sample which contains array of devices or even on single device level. The second filtering layer can be mounted on, glued to, coated evaporated or deposited on or mechanically or chemically attached above the bottom active cooling layer. Such deposition method comprises Chemical Vapor Deposition (CVD) including low (LPCVD) and high (HPCVD) pressure, electrodeposition, Physical Vapor Deposition (PVD) and casting deposition methods, thermal oxidation, epitaxial growth, thermal oxidation deposition etc. In other embodiments, the active cooling layer can be deposited using the previous fabrication method above, which is based on Si,SOI, Ge, GaAs substrate and wafers.

(69) Further, the success criteria for this process may be by evaluating the system active cooling efficiency via anti-Stokes scattering, however there are several design rules and guide lines which are recommended in this case:

(70) i. For mechanical, chemical or thermal bonding, bonding is highly recommended to avoid creation of a buffer layer, residues of the bonding martial, air gaps or other unwanted residue layers between the bottom active cooling to the top filtering layer.

(71) ii. The bonding between the layers should consider the thermal mechanical electrical and other stresses which can be applied on the system or device and degrade its performance. In this case, it is contemplated that environmental conditions of the device are considered such a humidity, temperature and electrical and magnetic inductances including DC and AC parasitic biases,

(72) iii. It is also contemplated within the scope of the present invention to a passivation layer, which is transparent to light radiation at the wavelength band and covers the system or device sensitive layers protecting the device top filtering and bottom anti-Stokes cooling layers and minimizing as much as possible their degradation over time. It is also contemplated that the cover layer isolates thermally and electrically the top and bottom layers of the device or system of the present invention. Further, it is contemplated that the cover layer protects the cooling device active layers from undesired environmental impacts, which can damage the active cooling layer properties and hence the system cooling properties. In further embodiment the at least one cover layer can be between the top and bottom layers or beneath the bottom layer.