我們的研究揭示了二維鹵化物鈣鈦礦中存在了高效的單光子上轉換光致發光現象，這項特質顯示了這些材料在雷射冷卻應用中的潛在價值。在本研究中，我們針對這些鈣鈦礦中的單光子上轉換光致發光機制進行了深入的探討，我們發現了它屬於反思托克斯光致發光的一種形式。
反思托克斯光致發光是藉由固態材料系統中的聲子來促成發射光子與吸收光子之間的能量轉移，這也被稱為聲子輔助上轉換或是熱能誘導上轉換機制。通過這種上轉換的過程，反思托克斯光致發光能夠有效的消耗固態材料系統中的熱能，藉此達成材料冷卻的效果，促成雷射冷卻的效應發生。
我們的研究成功展示了對二維PEA2PbI4鈣鈦礦材料進行雷射冷卻的可行性，並取得了令人矚目的成果，從室溫測量起，此材料的冷卻效果高達68.1 K。這一項重大發現不僅凸顯了光學冷卻和雷射冷卻技術在固態系統中的應用潛力，更為了各種電子和光電子元件的發展帶來了顯著的好處，這項研究開啟了一項新的研究方向，展開了一道新的大門發展未來新穎兼具高效的光電子雷射冷卻元件。

Our research has unveiled the presence of efficient single-photon up-conversion photoluminescence (UCPL) in 2D lead halide perovskites, demonstrating promising potential for laser cooling applications. This study introduces the intriguing phenomenon of single-photon UCPL in these perovskites, falling under the category of anti-Stokes photoluminescence (ASPL). ASPL relies on solid material phonons to facilitate the transition between emission and absorption, known as phonon-assisted up-conversion or thermal up-conversion. ASPL effectively manages thermal energy, resulting in material cooling. Our successful demonstration involved laser cooling of 2D PEA2PbI4 perovskite materials, resulting in an impressive cooling effect of up to 68.1 K. This significant finding suggests the feasibility of optical refrigeration and laser cooling for solid-state applications, offering substantial benefits to various electronic and optoelectronic devices.

1. Sheik-Bahae, M. and R.I. Epstein, Can laser light cool semiconductors? Physical Review Letters, 2004. 92(24): p. 247403.
2. Chen, W., A.G. Joly, and D.E. McCready, Upconversion luminescence from CdSe nanoparticles. Journal of Chemical Physics, 2005. 122(22): p. 224708.
3. Zhang, J., et al., Laser cooling of a semiconductor by 40 kelvin. Nature, 2013. 493(7433): p. 504-508.
4. Akizuki, N., et al., Efficient near-infrared up-conversion photoluminescence in carbon nanotubes. Nature Communications, 2015. 6: p. 8920.
5. Ha, S.T., et al., Laser cooling of organic-inorganic lead halide perovskites. Nature Photonics, 2016. 10(2): p. 115-121.
6. Gragossian, A., et al., Astigmatic Herriott cell for optical refrigeration. Optical Engineering, 2017. 56(1): p. 011110-011110.
7. Ma, X.M., et al., Mechanism of Single-Photon Upconversion Photoluminescence in All-Inorganic Perovskite Nanocrystals: The Role of Self-Trapped Excitons. Journal of Physical Chemistry Letters, 2019. 10(20): p. 5989-5996.
8. Yamada, T., T. Aharen, and Y. Kanemitsu, Upconverted excitonic photoluminescence from a two-dimensional lead-halide perovskite. Journal of Chemical Physics, 2019. 151(23): p. 234709.
9. Zhang, S.B., et al., Progress in laser cooling semiconductor nanocrystals and nanostructures. Npg Asia Materials, 2019. 11: p. 54.
10. Yin, Y.F., et al., Recent advances of two-dimensional material additives in hybrid perovskite solar cells. Nanotechnology, 2023. 34(17): p. 172001.
11. del Aguila, A.G., et al., Efficient up-conversion photoluminescence in all-inorganic lead halide perovskite nanocrystals. Nano Research, 2020. 13(7): p. 1962-1969.
12. Pokryshkin, N.S., V.N. Mantsevich, and V.Y. Timoshenko, Anti-Stokes Photoluminescence in Halide Perovskite Nanocrystals: From Understanding the Mechanism towards Application in Fully Solid-State Optical Cooling. Nanomaterials, 2023. 13(12): p. 1833.
13. Stokes, G.G., XXX. On the change of refrangibility of light. Philosophical Transactions of the Royal Society of London, 1852. 142: p. 463-562.
14. Thiede, J., et al., Cooling to 208K by optical refrigeration. Applied Physics Letters, 2005. 86(15): p. 154107.
15. Mungan, C.E., et al., Laser cooling of a solid by 16 K starting from room temperature. Physical Review Letters, 1997. 78(6): p. 1030-1033.
16. Luo, X., M.D. Eisaman, and T.R. Gosnell, Laser cooling of a solid by 21K starting from room temperature. Opt Lett, 1998. 23(8): p. 639-641.
17. Gosnell, T.R., Laser cooling of a solid by 65K starting from room temperature. Opt Lett, 1999. 24(15): p. 1041-1043.
18. Epstein, R.I., et al., OBSERVATION OF LASER-INDUCED FLUORESCENT COOLING OF A SOLID. Nature, 1995. 377(6549): p. 500-503.
19. Melgaard, S.D., et al., Optical refrigeration to 119 K, below National Institute of Standards and Technology cryogenic temperature. Optics Letters, 2013. 38(9): p. 1588-1590.
20. Melgaard, S.D., et al., Solid-state optical refrigeration to sub-100 Kelvin regime. Scientific Reports, 2016. 6(1): p. 20380.
100
21. Liu, Y., et al., Efficient, Stable, and Tunable Cold/Warm White Light from Lead-Free Halide Double Perovskites Cs2Zr1-xTexCl6. Advanced Optical Materials, 2021. 9(24): p. 2100815.
22. Yao, J.S., et al., Metal halide perovskites-based white light-emitting diodes. Journal of Physics-Photonics, 2022. 4(4): p. 042001.
23. Li, J.Z., H.Z. Wang, and D.H. Li, Self-trapped excitons in two-dimensional perovskites. Frontiers of Optoelectronics, 2020. 13(3): p. 225-234.
24. Prochazkova, A.J., et al., Anti-Stokes photoluminescence study on a methylammonium lead bromide nanoparticle film. Nanoscale, 2020. 12(31): p. 16556-16561.
25. Ye, S., et al., Low temperature synthesis of high-quality all-inorganic cesium lead halide perovskite nanocrystals in open air and their upconversion luminescence. Journal of Alloys and Compounds, 2018. 730: p. 62-70.
26. Gong, X., et al., Electron–phonon interaction in efficient perovskite blue emitters. Nature Materials, 2018. 17(6): p. 550-556.
27. Morozov, Y.V., et al., Photoluminescence Up-Conversion in CsPbBr3 Nanocrystals. Acs Energy Letters, 2017. 2(10): p. 2514-2515.
28. Yamada, T., T. Aharen, and Y. Kanemitsu, Up-converted photoluminescence from CH3NH3PbI3 perovskite semiconductors: Implications for laser cooling. Physical Review Materials, 2019. 3(2): p. 024601.
29. Lin, K.B., et al., Perovskite light-emitting diodes with external quantum efficiency exceeding 20 per cent. Nature, 2018. 562(7726): p. 245-248.
30. Wu, S.-C., et al., Carrier–Phonon Interaction Induced Large Negative Thermal-Optic Coefficient at Near Band Edge of Quasi-2D (PEA)2PbBr4 Perovskite. Advanced Functional Materials, 2023. 33(25): p. 2213427.
31. Li, W., et al., Decoupling excitons behavior of two-dimensional Ruddlesden-Popper PEA2PbI4 nanosheets. Journal of Alloys and Compounds, 2023. 936: p. 168312.
32. Duim, H., et al., The Impact of Stoichiometry on the Photophysical Properties of Ruddlesden-Popper Perovskites. Advanced Functional Materials, 2020. 30(5): p. 1907505.
33. Hong, K., et al., Low-dimensional halide perovskites: review and issues. Journal of Materials Chemistry C, 2018. 6(9): p. 2189-2209.
34. Zhang, Y., et al., Optical Properties of Two-Dimensional Perovskite Films of (C6H5C2H4NH3)2[PbI4] and (C6H5C2H4NH3)2 (CH3NH3)2[Pb3I10]. The Journal of Physical Chemistry Letters, 2019. 10(1): p. 13-19.
35. Lu, Y., et al., Remarkable dielectric breakdown strength enhancement of a PVDF terpolymer using a 2D hybrid organic inorganic perovskite as a functional additive. Journal of Materials Chemistry C, 2019. 7(43): p. 13390-13395.
36. Sutton, R.J., et al., Bandgap-Tunable Cesium Lead Halide Perovskites with High Thermal Stability for Efficient Solar Cells. Advanced Energy Materials, 2016. 6(8): p. 1502458.
37. Adjokatse, S., H.-H. Fang, and M.A. Loi, Broadly tunable metal halide perovskites for solid-state light-emission applications. Materials Today, 2017. 20(8): p. 413-424.
38. Li, M.L., et al., Amplified Spontaneous Emission Based on 2D Ruddlesden-Popper Perovskites. Advanced Functional Materials, 2018. 28(17): p. 1707006.
39. Zhang, H.H., et al., 2D Ruddlesden-Popper Perovskites Microring Laser Array. Advanced Materials, 2018. 30(15): p. 1706186.
101
40. Straus, D.B. and C.R. Kagan, Electrons, Excitons, and Phonons in Two-Dimensional Hybrid Perovskites: Connecting Structural, Optical, and Electronic Properties. J Phys Chem Lett, 2018. 9(6): p. 1434-1447.
41. Wang, Y., et al., Solution-Processed Low Threshold Vertical Cavity Surface Emitting Lasers from All-Inorganic Perovskite Nanocrystals. Advanced Functional Materials, 2017. 27(13): p. 1605088.
42. Bi, K., et al., Cesium lead halide perovskite quantum dot-based warm white light-emitting diodes with high color rendering index. Journal of Nanoparticle Research, 2017. 19(5): p. 1-8.
43. Bimberg, D., et al., Luminescence properties of semiconductor quantum dots. Journal of Luminescence, 1997. 72-4: p. 34-37.
44. Swarnkar, A., et al., Quantum dot-induced phase stabilization of α-CsPbI3 perovskite for high-efficiency photovoltaics. Science, 2016. 354(6308): p. 92-95.
45. Akkerman, Q.A., et al., Strongly emissive perovskite nanocrystal inks for high-voltage solar cells. Nature Energy, 2017. 2(2): p. 1-7.
46. Urban, J.M., et al., Revealing Excitonic Phonon Coupling in (PEA)2(MA)n-1PbnI3n+1 2D Layered Perovskites. Journal of Physical Chemistry Letters, 2020. 11(15): p. 5830-5835.
47. Gan, X.Y., et al., Role of organic cations in tuning the exciton binding energy of 2D lead iodide perovskite derivatives. Journal of Luminescence, 2023. 260: p. 119878.
48. Chen, H., et al., Structural and spectral dynamics of single-crystalline Ruddlesden-Popper phase halide perovskite blue light-emitting diodes. Science Advances, 2020. 6(4): p. eaay4045.
49. Zhou, C., et al., Highly Efficient Broadband Yellow Phosphor Based on Zero-Dimensional Tin Mixed-Halide Perovskite. ACS Applied Materials & Interfaces, 2017. 9(51): p. 44579-44583.
50. Lee, D., et al., EXCITON SELF-TRAPPING IN ZNSE-ZNTE ALLOYS. Physical Review Letters, 1987. 58(14): p. 1475-1478.
51. Benin, B.M., et al., Highly Emissive Self-Trapped Excitons in Fully Inorganic Zero-Dimensional Tin Halides. Angewandte Chemie-International Edition, 2018. 57(35): p. 11329-11333.
52. Yamada, Y., et al., Dynamic Optical Properties of CH3NH3PbI3 Single Crystals As Revealed by One- and Two-Photon Excited Photoluminescence Measurements. Journal of the American Chemical Society, 2015. 137(33): p. 10456-10459.
53. Yan, H.W., et al., Excitation-power dependence of the near-band-edge photoluminescence of ZnO inverse opals and nanocrystal films. Journal of Luminescence, 2008. 128(2): p. 245-249.
54. He, H.P., et al., Exciton localization in solution-processed organolead trihalide perovskites. Nature Communications, 2016. 7: p. 10896.
55. Rubino, A., et al., Disentangling Electron-Phonon Coupling and Thermal Expansion Effects in the Band Gap Renormalization of Perovskite Nanocrystals. Journal of Physical Chemistry Letters, 2021. 12(1): p. 569-575.
56. Wright, A.D., et al., Electron-phonon coupling in hybrid lead halide perovskites. Nature Communications, 2016. 7: p. 11755.
57. Zhang, B.B., et al., Electron-Phonon Coupling Suppression by Enhanced Lattice Rigidity in 2D Perovskite Single Crystals for High-Performance X-Ray Detection. Advanced Materials, 2023. 35(7): p. 2208875.
58. Plummer, E.W., et al., Enhanced electron-phonon coupling at metal surfaces. Progress in Surface Science, 2003. 74(1-8): p. 251-268.
102
59. Foley, B.J., et al., Temperature dependent energy levels of methylammonium lead iodide perovskite. Applied Physics Letters, 2015. 106(24): p. 243904.
60. Luckert, F., et al., Excitation power and temperature dependence of excitons in CuInSe2. Journal of Applied Physics, 2012. 111(9): p. 093507.
61. Neutzner, S., et al., Exciton-polaron spectral structures in two-dimensional hybrid lead-halide perovskites. Physical Review Materials, 2018. 2(6): p. 064605.