The upconversion quantum yield (UCQY): a review to standardize the measurement methodology, improve comparability, and define efficiency standards

References

• Auzel F. Upconversion and anti-stokes processes with f and d ions in solids. Chem Rev. 2004;104(1):139–174.
   PubMed Web of Science ®Google Scholar
• Chen J , Zhao JX. Upconversion nanomaterials: synthesis, mechanism, and applications in sensing. Sensors. 2012;12(3):2414–2435.
   PubMed Web of Science ®Google Scholar
• Menyuk N , Dwight K , Pierce JW. NaYF4: Yb,Er—an efficient upconversion phosphor. Appl Phys Lett. 1972;21(4):159–161.
   Web of Science ®Google Scholar
• Kramer KW , Biner D , Frei G , et al. Hexagonal sodium yttrium fluoride based green and blue emitting upconversion phosphors. Chem Mater. 2004;16(7):1244–1251.
   Web of Science ®Google Scholar
• Przybylska D , Ekner-Grzyb A , Grześkowiak BF , et al. Upconverting SrF 2 nanoparticles doped with Yb 3+/Ho 3+, Yb 3+/Er 3+ and Yb 3+/Tm 3+ ions–optimisation of synthesis method, structural, spectroscopic and cytotoxicity studies. Sci Rep. 2019;9(1):1–12.
   PubMed Web of Science ®Google Scholar
• Skripka A , Cheng T , Jones CMS , et al. Spectral characterization of LiYbF4 upconverting nanoparticles. Nanoscale. 2020;12(33):17545–17554.
   PubMed Web of Science ®Google Scholar
• Pollnau M . Power dependence of upconversion luminescence in lanthanide and transition-metal-ion systems. Phys Rev B. 2000;61:3337.
   Web of Science ®Google Scholar
• Bünzli J-CG , Eliseeva SV . Basics of lanthanide photophysics. lanthanide luminescence. Springer Series on Fluorescence. Berlin, Heidelberg: Springer; 2010. p. 1–45.
   Google Scholar
• Wang F , Liu X . Recent advances in the chemistry of lanthanide-doped upconversion nanocrystals. Chem Soc Rev. 2009 Apr;38(4):976–989.
   PubMed Web of Science ®Google Scholar
• Zhou J , Liu Q , Feng W , et al. Upconversion luminescent materials: advances and applications. Chem Rev. 2015;115(1):395–465.
   PubMed Web of Science ®Google Scholar
• Zhao J , Lu Z , Yin Y , et al. Upconversion luminescence with tunable lifetime in NaYF 4: Yb, Er nanocrystals: role of nanocrystal size. Nanoscale. 2013;5(3):944–952.
   PubMed Web of Science ®Google Scholar
• Kraft M , Würth C , Muhr V , et al. Particle-size-dependent upconversion luminescence of NaYF 4: Yb, Er nanoparticles in organic solvents and water at different excitation power densities. Nano Res. 2018;11(12):6360–6374.
   Web of Science ®Google Scholar
• Fischer S , Martín-Rodríguez R , Fröhlich B , et al. Upconversion quantum yield of Er3+-doped β-NaYF4 and Gd2O2S: the effects of host lattice, Er3+ doping, and excitation spectrum bandwidth. J Lumin. 2014;153:281–287.
   Web of Science ®Google Scholar
• Werts MH . Making sense of lanthanide luminescence. Sci Prog. 2005;88(2):101–131.
   PubMedGoogle Scholar
• Kaiser M , Würth C , Kraft M , et al. Power-dependent upconversion quantum yield of NaYF 4: Yb 3+, Er 3+ nano-and micrometer-sized particles–measurements and simulations. Nanoscale. 2017;9(28):10051–10058.
   PubMed Web of Science ®Google Scholar
• Vetrone F , Naccache R , Mahalingam V , et al. The active‐core/active‐shell approach: a strategy to enhance the upconversion luminescence in lanthanide‐doped nanoparticles. Adv Funct Mater. 2009;19(18):2924–2929.
   Web of Science ®Google Scholar
• Fischer S , Bronstein ND , Swabeck JK , et al. Precise tuning of surface quenching for luminescence enhancement in core–shell lanthanide-doped nanocrystals. Nano Lett. 2016;16(11):7241–7247.
   PubMed Web of Science ®Google Scholar
• You M , Zhong J , Hong Y , et al. Inkjet printing of upconversion nanoparticles for anti-counterfeit applications. Nanoscale. 2015;7(10):4423–4431.
   PubMed Web of Science ®Google Scholar
• Vetrone F , Capobianco JA . Lanthanide-doped fluoride nanoparticles: luminescence, upconversion, and biological applications. Int J Nanotechnol. 2008;5(9–12):1306–1339.
   Web of Science ®Google Scholar
• Lee G , Park YI . Lanthanide-doped upconversion nanocarriers for drug and gene delivery. Nanomaterials. 2018;8(7):511.
   Web of Science ®Google Scholar
• Rafique R , Kailasa SK , Park TJ . Recent advances of upconversion nanoparticles in theranostics and bioimaging applications. Trends Analyt Chem. 2019;120:115646.
   Web of Science ®Google Scholar
• Hemmer E , Acosta-Mora P , Méndez-Ramos J , et al. Optical nanoprobes for biomedical applications: shining a light on upconverting and near-infrared emitting nanoparticles for imaging, thermal sensing, and photodynamic therapy. J Mater Chem. 2017;5(23):4365–4392.
   Web of Science ®Google Scholar
• Hemmer E , Quintanilla M , Legare F , et al. Temperature-induced energy transfer in dye-conjugated upconverting nanoparticles: a new candidate for nanothermometry. Chem Mater. 2015;27(1):235–244.
   Web of Science ®Google Scholar
• Goldschmidt JC , Fischer S . Upconversion for photovoltaics–a review of materials, devices and concepts for performance enhancement. Adv Opt Mater. 2015;3(4):510–535.
   Web of Science ®Google Scholar
• Clarivate . [cited 2021 May 20 ]. Available from: http://apps.webofknowledge.com/WOS_GeneralSearch_input.do?product=WOS&search_mode=GeneralSearch&SID=D2OM4Jc3Wwq8RQLWpVW&preferencesSaved=
   Google Scholar
• Park W , Lu D , Ahn S . Plasmon enhancement of luminescence upconversion. Chem Soc Rev. 2015;44(10):2940–2962.
   PubMed Web of Science ®Google Scholar
• Herter B , Wolf S , Fischer S , et al., editors. Effects of photonic structures on upconversion. Photonics for Solar Energy Systems IV. International Society for Optics and Photonics; Brussels, Belgium: SPIE Photonics Europe; 2012.
   Google Scholar
• Wisser MD , Fischer S , Siefe C , et al. Improving quantum yield of upconverting nanoparticles in aqueous media via emission sensitization. Nano Lett. 2018;18(4):2689–2695.
   PubMed Web of Science ®Google Scholar
• Auzel F , Pecile D . Absolute efficiency for IR to blue conversion materials and theoretical prediction for optimized matrices. J Lumin. 1976;11(5–6):321–330.
   Web of Science ®Google Scholar
• Auzel F , Pecile D . Comparison and efficiency of materials for summation of photons assisted by energy transfer. J Lumin. 1973;8(1):32–43.
   Google Scholar
• Tan MC , Connolly J , Riman RE . Optical efficiency of short wave infrared emitting phosphors. J Phys Chem C. 2011;115(36):17952–17957.
   Web of Science ®Google Scholar
• Tan MC , Al-Baroudi L , Riman RE . Surfactant effects on efficiency enhancement of infrared-to-visible upconversion emissions of NaYF4: Yb-Er. ACS Appl Mater Interfaces. 2011;3(10):3910–3915.
   PubMed Web of Science ®Google Scholar
• Auzel, F.E., Materials and devices using double-pumped-phosphors with energy transfer. Proceedings of the IEEE; New York (NY): IEEE; 1973.
   Google Scholar
• Rapaport A , Milliez J , Bass M , et al. Review of the properties of up-conversion phosphors for new emissive displays. J Disp Technol. 2006;2(1):68.
   Google Scholar
• Rapaport A , Milliez J , Szipőcs F , et al. Properties of a new, efficient, blue-emitting material for applications in upconversion displays: Yb, Tm: KY 3 F 10. Appl Opt. 2004;43(35):6477–6480.
   PubMed Web of Science ®Google Scholar
• Ohwaki J , Wang Y . New efficient upconversion phosphor BaCl/sub 2: Er under 1.5 mu m excitation. Electron Lett. 1993;29(4):351–352.
   Web of Science ®Google Scholar
• Shao W , Chen G , Damasco J , et al. Enhanced upconversion emission in colloidal (NaYF 4: Er 3+)/NaYF 4 core/shell nanoparticles excited at 1523 nm. Opt Lett. 2014;39(6):1386–1389.
   PubMed Web of Science ®Google Scholar
• Page RH , Schaffers KI , Waide PA , et al., editors. Upconversion-pumped luminescence efficiency of rare-earth-doped hosts sensitized with trivalent ytterbium. JOSA B. 1998;15(3):996–1008.
   Google Scholar
• Etchart I , Hernández I , Huignard A , et al. Efficient oxide phosphors for light upconversion; green emission from Yb 3+ and Ho 3+ co-doped Ln 2 BaZnO 5 (Ln= Y, Gd). J Mater Chem. 2011;21(5):1387–1394.
   Web of Science ®Google Scholar
• Quimby R , Drexhage M , Suscavage M . Efficient frequency up-conversion via energy transfer in fluoride glasses. Electron Lett. 1987;23(1):32–34.
   Web of Science ®Google Scholar
• Li T , Guo C-F , Yang Y-M , et al. Efficient green up-conversion emission in Yb3+/Ho3+ co-doped CaIn2O4. Acta Materialia. 2013;61(19):7481–7487.
   Web of Science ®Google Scholar
• Yasyrkina D , Kuznetsov S , Ryabova A , et al. Dependence of quantum yield of up-conversion luminescence on the composition of fluorite-type solid solution nay 1-x-yyb XEr YF 4. Наносистемы: физика, химия, математика. 2013;4(5):648–656.
   Google Scholar
• Zhang J , Yang Y , Mi C , et al. White up-conversion luminescence power and efficiency in Yb 3+-, Er 3+-and Tm 3+-doped BaIn 6 Y 2 O 13. Dalton Trans. 2015;44(3):1093–1101.
   PubMed Web of Science ®Google Scholar
• Yeh D , Sibley W , Schneider I , et al. Intensity‐dependent upconversion efficiencies of Er3+ ions in heavy‐metal fluoride glass. J Appl Phys. 1991;69(3):1648–1653.
   Web of Science ®Google Scholar
• Pollack S , Chang D , Moise N . Upconversion‐pumped infrared erbium laser. J Appl Phys. 1986;60(12):4077–4086.
   Web of Science ®Google Scholar
• Etchart I , Hernández I , Huignard A , et al. Oxide phosphors for light upconversion; Yb3+ and Tm3+ co-doped Y2BaZnO5. J Appl Phys. 2011;109(6):063104.
   Web of Science ®Google Scholar
• Etchart I , Huignard A , Bérard M , et al. Oxide phosphors for efficient light upconversion: Yb3+ and Er3+ co-doped Ln 2 BaZnO 5 (Ln= Y, Gd). J Mater Chem. 2010;20(19):3989–3994.
   Web of Science ®Google Scholar
• Etchart I , Bérard M , Laroche M , et al. Efficient white light emission by upconversion in Yb 3+-, Er 3+-and Tm 3+-doped Y 2 BaZnO 5. Chem Comm. 2011;47(22):6263–6265.
   PubMed Web of Science ®Google Scholar
• Vavilov S . The fluorescence efficiency of dye solutions. Z Phys. 1924;22:266–272.
   Google Scholar
• Demasa J , Crosby G . The measurement of photoluminescence quantum yields. A review. J Chem Phys. 1968;48:4726.
   Google Scholar
• Parker C , Barnes W . Some experiments with spectrofluorimeters and filter fluorimeters. Analyst. 1957;82(978):606–618.
   Web of Science ®Google Scholar
• Zepp RG . Quantum yields for reaction of pollutants in dilute aqueous solution. Environ Sci Technol. 1978;12(3):327–329.
   Web of Science ®Google Scholar
• Lakowicz JR . Topics in fluorescence spectroscopy: principles. In: Joseph R. Lakowicz, editor Vol. 2. Springer Science & Business Media; Springer (US); 1992.
   Google Scholar
• Weber G , Teale F . Determination of the absolute quantum yield of fluorescent solutions. Trans Faraday Soc. 1957;53:646–655.
   Google Scholar
• Thomson CG , Jones CM , Rosair G , et al. Continuous-flow synthesis and application of polymer-supported BODIPY photosensitisers for the generation of singlet oxygen; process optimised by in-line NMR spectroscopy. J Flow Chem. 2020;10(1):327–345
   Web of Science ®Google Scholar
• Goedhart J , Von Stetten D , Noirclerc-Savoye M , et al. Structure-guided evolution of cyan fluorescent proteins towards a quantum yield of 93%. Nat Commun. 2012;3(1):1–9.
   Web of Science ®Google Scholar
• Ruiz D , Mizrahi M , Santos HD , et al. Synthesis and characterization of Ag 2 S and Ag 2 S/Ag 2 (S, Se) NIR nanocrystals. Nanoscale. 2019;11(18):9194–9200.
   PubMed Web of Science ®Google Scholar
• Santos HD , Gutiérrez IZ , Shen Y , et al. Ultrafast photochemistry produces superbright short-wave infrared dots for low-dose in vivo imaging. Nat Commun. 2020;11(1):1–12.
   PubMed Web of Science ®Google Scholar
• Soldan G , Aljuhani MA , Bootharaju MS , et al. Gold doping of silver nanoclusters: a 26‐Fold enhancement in the luminescence quantum yield. Angew Chem. 2016;55(19):5843–5847.
   Google Scholar
• Greenham N , Samuel I , Hayes G , et al. Measurement of absolute photoluminescence quantum efficiencies in conjugated polymers. Chem Phys Lett. 1995;241(1–2):89–96.
   Web of Science ®Google Scholar
• Suzuki K , Endo A , Yoshihara T , et al., editors. Photophysical study of iridium complexes by absolute photoluminescence quantum yield measurements using an integrating sphere. In: Organic light emitting materials and devices XIII. International Society for Optics and Photonics; San Diego, CA: SPIE Photonic Devices + Applications; 2009.
   Google Scholar
• Crochet J , Clemens M , Hertel T . Quantum yield heterogeneities of aqueous single-wall carbon nanotube suspensions. J Am Chem Soc. 2007;129(26):8058–8059.
   PubMed Web of Science ®Google Scholar
• May PS , Berry M . Tutorial on the acquisition, analysis, and interpretation of upconversion luminescence data. Methods Appl Fluoresc. 2019;7(2):023001.
   PubMed Web of Science ®Google Scholar
• Faulkner DO , McDowell JJ , Price AJ , et al. Measurement of absolute photoluminescence quantum yields using integrating spheres–which way to go? Laser Photonics Rev. 2012;6(6):802–806.
   Web of Science ®Google Scholar
• Mousavi M , Thomasson B , Li M , et al. Beam-profile-compensated quantum yield measurements of upconverting nanoparticles. Phys Chem Chem Phys. 2017;19(33):22016–22022.
   PubMed Web of Science ®Google Scholar
• Chen W , Song F , Tang S , et al. Red-to-blue photon up-conversion with high efficiency based on a TADF fluorescein derivative. Chem Comm. 2019;55(30):4375–4378.
   PubMed Web of Science ®Google Scholar
• Joseph RE , Jiménez C , Hudry D , et al. Critical power density: a metric to compare the excitation power density dependence of photon upconversion in different inorganic host materials. J Phys Chem A. 2019;123(31):6799–6811.
   PubMed Web of Science ®Google Scholar
• Fischer S , Johnson NJ , Pichaandi J , et al. Upconverting core-shell nanocrystals with high quantum yield under low irradiance: on the role of isotropic and thick shells. J Appl Phys. 2015;118(19):193105.
   Web of Science ®Google Scholar
• Parker CA , Rees W . Correction of fluorescence spectra and measurement of fluorescence quantum efficiency. Analyst. 1960;85(1013):587–600.
   Web of Science ®Google Scholar
• Levitus M . Tutorial: measurement of fluorescence spectra and determination of relative fluorescence quantum yields of transparent samples. Methods Appl Fluoresc. 2020;8(3):033001.
   PubMed Web of Science ®Google Scholar
• Rurack K . Fluorescence quantum yields: methods of determination and standards. In: Ute Resch-Genger, editor. Standardization and quality assurance in fluorescence measurements I. Berlin, Heidelberg: Springer; 2008. p. 101–145.
   Google Scholar
• Brouwer AM . Standards for photoluminescence quantum yield measurements in solution (IUPAC technical report). Pure Appl Chem. 2011;83(12):2213–2228.
   Web of Science ®Google Scholar
• Würth C , Grabolle M , Pauli J , et al. Relative and absolute determination of fluorescence quantum yields of transparent samples. Nat Protoc. 2013;8(8):1535–1550.
   PubMed Web of Science ®Google Scholar
• Würth C , Geißler D , Behnke T , et al. Critical review of the determination of photoluminescence quantum yields of luminescent reporters. Anal Bioanal Chem. 2015;407(1):59–78.
   PubMed Web of Science ®Google Scholar
• Fischer S , Fröhlich B , Steinkemper H , et al. Absolute upconversion quantum yield of β-NaYF4 doped with Er3+ and external quantum efficiency of upconverter solar cell devices under broad-band excitation considering spectral mismatch corrections. Sol Energy Mater Sol Cells. 2014;122:197–207.
   Web of Science ®Google Scholar
• Rao CS , Kityk I , Srikumar T , et al. Spectroscopy features of Pr3+ and Er3+ ions in Li2O–ZrO2–SiO2 glass matrices mixed with some sesquioxides. J Alloys Compd. 2011;509(37):9230–9239.
   Web of Science ®Google Scholar
• Rozanski M , Wisniewski K , Szatkowski J , et al. Effect of thermal treatment on excited state spectroscopy of oxyfluoride borosilicate glass activated by Pr3+ ions. Opt Mater. 2009;31(3):548–553.
   Web of Science ®Google Scholar
• Meijer MS , Rojas-Gutierrez PA , Busko D , et al. Absolute upconversion quantum yields of blue-emitting LiYF4: Yb(3+), Tm(3+)upconverting nanoparticles. Phys Chem Chem Phys. 2018 Sep 12;20(35):22556–22562.
   PubMed Web of Science ®Google Scholar
• Liu H , Xu CT , Lindgren D , et al. Balancing power density based quantum yield characterization of upconverting nanoparticles for arbitrary excitation intensities. Nanoscale. 2013;5(11):4770–4775.
   PubMed Web of Science ®Google Scholar
• Wisser MD , Fischer S , Maurer PC , et al. Enhancing quantum yield via local symmetry distortion in lanthanide-based upconverting nanoparticles. ACS Photonics. 2016;3(8):1523–1530.
   Web of Science ®Google Scholar
• Porres L , Holland A , Palsson LO , et al. Absolute measurements of photoluminescence quantum yields of solutions using an integrating sphere. J Fluoresc. 2006 Mar;16(2):267–272.
   PubMed Web of Science ®Google Scholar
• Würth C , Lochmann C , Spieles M , et al. Evaluation of a commercial integrating sphere setup for the determination of absolute photoluminescence quantum yields of dilute dye solutions. Appl Spectrosc. 2010;64(7):733–741.
   PubMed Web of Science ®Google Scholar
• MacDougall SK , Ivaturi A , Marques-Hueso J , et al. Measurement procedure for absolute broadband infrared up-conversion photoluminescent quantum yields: correcting for absorption/re-emission. Rev Sci Instrum. 2014;85(6):063109.
   PubMed Web of Science ®Google Scholar
• Boyer JC , Van Veggel FC . Absolute quantum yield measurements of colloidal NaYF4: Er3+, Yb3+ upconverting nanoparticles. Nanoscale. 2010 Aug;2(8):1417–1419.
   PubMed Web of Science ®Google Scholar
• de Mello JC , Wittmann HF , Friend RH . An improved experimental determination of external photoluminescence quantum efficiency. Adv Mater. 1997;9(3):230–232.
   Web of Science ®Google Scholar
• Zou Q , Huang P , Zheng W , et al. Cooperative and non-cooperative sensitization upconversion in lanthanide-doped LiYbF 4 nanoparticles. Nanoscale. 2017;9(19):6521–6528.
   PubMed Web of Science ®Google Scholar
• Gao G , Busko D , Joseph R , et al. Highly efficient La2O3: Yb3+, Tm3+ single-band NIR-to-NIR upconverting microcrystals for anti-counterfeiting applications. ACS Appl Mater Interfaces. 2018;10(46):39851–39859.
   PubMed Web of Science ®Google Scholar
• Kuznetsov S , Ermakova Y , Voronov V , et al. Up-conversion quantum yields of SrF 2: Yb 3+, Er 3+ sub-micron particles prepared by precipitation from aqueous solution. J Mater Chem C. 2018;6(3):598–604.
   Web of Science ®Google Scholar
• Zhong Y , Tian G , Gu Z , et al. Elimination of photon quenching by a transition layer to fabricate a quenching‐shield sandwich structure for 800 nm excited upconversion luminescence of Nd3+‐sensitized nanoparticles. Adv Mater. 2014;26(18):2831–2837.
   PubMed Web of Science ®Google Scholar
• Duan Q , Qin F , Wang P , et al. Upconversion emission efficiency of Tb 3+-Yb 3+ codoped glass. JOSA B. 2013;30(2):456–459.
   Web of Science ®Google Scholar
• Stanton IN , Ayres JA , Stecher JT , et al. Power-dependent radiant flux and absolute quantum yields of upconversion nanocrystals under continuous and pulsed excitation. J Phys Chem C. 2018;122(1):252–259.
   Web of Science ®Google Scholar
• Faulkner DO , Petrov S , Perovic DD , et al. Absolute quantum yields in NaYF4: Er, Yb upconverters–synthesis temperature and power dependence. J Mater Chem. 2012;22(46):24330–24334.
   Web of Science ®Google Scholar
• Gao G , Busko D , Kauffmann-Weiss S , et al. Finely-tuned NIR-to-visible up-conversion in La 2 O 3: Yb 3+, Er 3+ microcrystals with high quantum yield. J Mater Chem C. 2017;5(42):11010–11017.
   Web of Science ®Google Scholar
• May PS , Baride A , Hossan MY , et al. Measuring the internal quantum yield of upconversion luminescence for ytterbium-sensitized upconversion phosphors using the ytterbium (iii) emission as an internal standard. Nanoscale. 2018;10(36):17212–17226.
   PubMed Web of Science ®Google Scholar
• Khosrofian JM , Garetz BA . Measurement of a Gaussian laser beam diameter through the direct inversion of knife-edge data. Appl Opt. 1983;22(21):3406–3410.
   PubMed Web of Science ®Google Scholar
• Pilch-Wrobel A , Czaban B , Wawrzyńczyk D , et al. Quantum yield measurements of Yb, Ho co-doped upconverting nanomaterials: the impact of methods, reference materials and concentration. J Lumin. 2018;198:482–487.
   Web of Science ®Google Scholar
• Martini M , Montagna M , Ou M , et al. How to measure quantum yields in scattering media: application to the quantum yield measurement of fluorescein molecules encapsulated in sub-100 nm silica particles. J Appl Phys. 2009;106(9):094304.
   Web of Science ®Google Scholar
• Würth C , Resch-Genger U . Determination of photoluminescence quantum yields of scattering media with an integrating sphere: direct and indirect illumination. Appl Spectrosc. 2015;69(6):749–759.
   PubMed Web of Science ®Google Scholar
• Jones CM , Panov N , Skripka A , et al. Effect of light scattering on upconversion photoluminescence quantum yield in microscale-to-nanoscale materials. Opt Express. 2020;28(15):22803–22818.
   PubMed Web of Science ®Google Scholar
• Jones CM , Biner D , Krämer KW , et al. Optimized photoluminescence quantum yield in upconversion composites considering the scattering, inner-filter effects, thickness, self-absorption, and temperature; 2021. (Submitted to Scientific Reports).
   Google Scholar
• Jones CM , Wang X , Marques-Hueso J , editors. Scattering media influences photoluminescence quantum yield of upconversion microtube phosphor. 3D Image Acquisition and Display: Technology, Perception and Applications. Washington, DC: Optical Society of America; 2020.
   Google Scholar
• Ivaturi A , MacDougall SKW , Martín-Rodríguez R , et al. Optimizing infrared to near infrared upconversion quantum yield of β-NaYF4: Er3+in fluoropolymer matrix for photovoltaic devices. J Appl Phys. 2013;114(1). DOI:https://doi.org/10.1063/1.4812578.
   Google Scholar
• Lv R , Feng M , Parak WJ . Up-conversion luminescence properties of lanthanide-gold hybrid nanoparticles as analyzed with discrete dipole approximation. Nanomaterials. 2018;8(12):989.
   Web of Science ®Google Scholar
• Fischer S , Favilla E , Tonelli M , et al. Record efficient upconverter solar cell devices with optimized bifacial silicon solar cells and monocrystalline BaY2F8: 30% Er3+ upconverter. Sol Energy Mater Sol Cells. 2015;136:127–134.
   Web of Science ®Google Scholar
• Kimball J , Chavez JL , Ceresa L , et al. On the origin and correction for inner filter effects in fluorescence. Part I: primary inner filter effect-the proper approach for sample absorbance correction. Methods Appl Fluoresc. 2020;8(3):033002.
   PubMed Web of Science ®Google Scholar
• Douglas AS , Donald MW . Principles of instrumental analysis. Vol. 104. Cengage Learning; 2017; Boston, MA.
   Google Scholar
• Fonin AV , Sulatskaya AI , Kuznetsova IM , et al. Fluorescence of dyes in solutions with high absorbance. Inner filter effect correction. PLoS One. 2014;9(7):e103878.
   PubMed Web of Science ®Google Scholar
• Ahn T-S , Al-Kaysi RO , Müller AM , et al. Self-absorption correction for solid-state photoluminescence quantum yields obtained from integrating sphere measurements. Rev Sci Instrum. 2007;78(8):086105.
   PubMed Web of Science ®Google Scholar
• Wilson LR , Rowan BC , Robertson N , et al. Characterization and reduction of reabsorption losses in luminescent solar concentrators. Appl Opt. 2010;49(9):1651–1661.
   PubMed Web of Science ®Google Scholar
• Gao D , Tian D , Zhang X , et al. Simultaneous quasi-one-dimensional propagation and tuning of upconversion luminescence through waveguide effect. Sci Rep. 2016;6:22433.
   PubMed Web of Science ®Google Scholar
• Boccolini A , Favilla E , Tonelli M , et al. Highly efficient upconversion in Er 3+ doped BaY 2 F 8 single crystals: dependence of quantum yield on excitation wavelength and thickness. Opt Express. 2015;23(15):A903–A915.
   PubMed Web of Science ®Google Scholar
• Boccolini A , Marques-Hueso J , Richards BS . Self-absorption in upconverter luminescent layers: impact on quantum yield measurements and on designing optimized photovoltaic devices. Opt Lett. 2014 May 15;39(10):2904–2907.
   PubMed Web of Science ®Google Scholar
• Pilch A , Würth C , Kaiser M , et al. Shaping luminescent properties of Yb3+ and Ho3+ Co‐doped upconverting core–shell β‐NaYF4 nanoparticles by dopant distribution and spacing. Small. 2017;13(47):1701635.
   Web of Science ®Google Scholar
• Kraft M , Würth C , Palo E , et al. Colour-optimized quantum yields of Yb, Tm Co-doped upconversion nanocrystals. Methods Appl Fluoresc. 2019;7(2):024001.
   PubMed Web of Science ®Google Scholar
• Homann C , Krukewitt L , Frenzel F , et al. NaYF4: Yb, Er/NaYF4 core/shell nanocrystals with high upconversion luminescence quantum yield. Angew Chem. 2018;57(28):8765–8769.
   Google Scholar
• Würth C , Fischer S , Grauel B , et al. Quantum yields, surface quenching, and passivation efficiency for ultrasmall core/shell upconverting nanoparticles. J Am Chem Soc. 2018;140(14):4922–4928.
   PubMed Web of Science ®Google Scholar
• Wu X , Zhang Y , Takle K , et al. Dye-sensitized core/active shell upconversion nanoparticles for optogenetics and bioimaging applications. ACS Nano. 2016;10(1):1060–1066.
   PubMed Web of Science ®Google Scholar
• Hyppänen I , Höysniemi N , Arppe R , et al. Environmental impact on the excitation path of the red upconversion emission of nanocrystalline NaYF4: Yb3+, Er3+. J Phys Chem C. 2017;121(12):6924–6929.
   Web of Science ®Google Scholar
• Feng P , Pan Y , Ye H . Core–shell structured NaYF 4: Yb, Tm@ CdS composite for enhanced photocatalytic properties. RSC Adv. 2018;8(61):35306–35313.
   PubMed Web of Science ®Google Scholar
• Hossan MY , Hor A , Luu Q , et al. Explaining the nanoscale effect in the upconversion dynamics of β-NaYF4: Yb3+, Er3+ core and core–shell nanocrystals. J Phys Chem C. 2017;121(30):16592–16606.
   Web of Science ®Google Scholar
• Hong A-R , Kim SY , Cho S-H , et al. Facile synthesis of multicolor tunable ultrasmall LiYF4: Yb, Tm, Er/LiGdF4 core/shell upconversion nanophosphors with sub-10 nm size. Dyes Pigm. 2017;139:831–838.
   Web of Science ®Google Scholar
• Qiu Z , Shu J , Tang D . Near-infrared-to-ultraviolet light-mediated photoelectrochemical aptasensing platform for cancer biomarker based on core–shell NaYF4: Yb, Tm@ TiO2 upconversion microrods. Anal Chem. 2018;90(1):1021–1028.
   PubMed Web of Science ®Google Scholar
• Chen X , Peng D , Ju Q , et al. Photon upconversion in core–shell nanoparticles. Chem Soc Rev. 2015;44(6):1318–1330.
   PubMed Web of Science ®Google Scholar
• Zhang Y , Liu X , Lang Y , et al. Synthesis of ultra-small BaLuF 5: Yb 3+, Er 3+@ BaLuF 5: Yb 3+ active-core–active-shell nanoparticles with enhanced up-conversion and down-conversion luminescence by a layer-by-layer strategy. J Mater Chem C. 2015;3(9):2045–2053.
   Web of Science ®Google Scholar
• Shen J , Chen G , Ohulchanskyy TY , et al. Tunable near infrared to ultraviolet upconversion luminescence enhancement in (α‐NaYF4: Yb, Tm)/CaF2 core/shell nanoparticles for In situ real‐time recorded biocompatible photoactivation. small. 2013;9(19):3213–3217.
   PubMed Web of Science ®Google Scholar
• Wang F , Deng R , Wang J , et al. Tuning upconversion through energy migration in core–shell nanoparticles. Nat Mater. 2011;10(12):968–973.
   PubMed Web of Science ®Google Scholar
• Guang-Shun Y , Chow G-M . Water-soluble NaYF4: Yb,Er(Tm)/NaYF4Polymer/core/shell/shell nanoparticles with significant enhancment of upconversion fluorescence. Chem Mater. 2007;19(3):341–343.
   Web of Science ®Google Scholar
• Chen G , Shen J , Ohulchanskyy TY , et al. (α-NaYbF4: Tm3+)/CaF2 core/shell nanoparticles with efficient near-infrared to near-infrared upconversion for high-contrast deep tissue bioimaging. ACS Nano. 2012;6(9):8280–8287.
   PubMed Web of Science ®Google Scholar
• Würth C , Kaiser M , Wilhelm S , et al. Excitation power dependent population pathways and absolute quantum yields of upconversion nanoparticles in different solvents. Nanoscale. 2017;9(12):4283–4294.
   PubMed Web of Science ®Google Scholar
• Ishida H , Tobita S , Hasegawa Y , et al. Recent advances in instrumentation for absolute emission quantum yield measurements. Coord Chem Rev. 2010;254(21–22):2449–2458.
   Web of Science ®Google Scholar
• Balabhadra S , Debasu M , Brites C , et al. A cost-effective quantum yield measurement setup for upconverting nanoparticles. J Lumin. 2017;189:64–70.
   Web of Science ®Google Scholar
• Joseph RE , Busko D , Hudry D , et al. A method for correcting the excitation power density dependence of upconversion emission due to laser-induced heating. Opt Mater. 2018;82:65–70.
   Web of Science ®Google Scholar
• Johnson AR , Lee S-J , Klein J , et al. Absolute photoluminescence quantum efficiency measurement of light-emitting thin films. Rev Sci Instrum. 2007;78(9):096101.
   PubMed Web of Science ®Google Scholar
• Wei Y , Ou H . Photoluminescence quantum yield of fluorescent silicon carbide determined by an integrating sphere setup. ACS Omega. 2019;4(13):15488–15495.
   PubMed Web of Science ®Google Scholar
• Fischer S , Mehlenbacher RD , Lay A , et al. Small alkaline-earth-based core/shell nanoparticles for efficient upconversion. Nano Lett. 2019;19(6):3878–3885.
   PubMed Web of Science ®Google Scholar
• Marques-Hueso J , Chen D , MacDougall SK , et al., editors. Advances in spectral conversion for photovoltaics: up-converting Er3+ doped YF3 nano-crystals in transparent glass ceramic. In: Next generation (Nano) photonic and cell technologies for solar energy conversion II. International Society for Optics and Photonics; San Diego, CA: SPIE Solar Energy; 2011. p.8111.
   Google Scholar
• Shalav A , Richards B , Green M . Luminescent layers for enhanced silicon solar cell performance: up-conversion. Sol Energy Mater Sol Cells. 2007;91(9):829–842.
   Web of Science ®Google Scholar
• Fischer S , Goldschmidt J , Löper P , et al. Enhancement of silicon solar cell efficiency by upconversion: optical and electrical characterization. J Appl Phys. 2010;108(4):044912.
   Web of Science ®Google Scholar
• Gibbons J , Jones CM , Bennett NS , et al. Determination of the refractive index of BaY2F8: Er3+ (0.5 mol% to 30 mol%) in the 300 nm–1800 nm range by ellipsometry; a record-breaking upconversion material. J Lumin. 2020;230:117639.
   Web of Science ®Google Scholar
• MacDougall SK , Ivaturi A , Marques-Hueso J , et al. Ultra-high photoluminescent quantum yield of beta-NaYF4: 10% Er3+ via broadband excitation of upconversion for photovoltaic devices. Opt Express. 2012 Nov 5;20(106):A879–87.
   PubMed Web of Science ®Google Scholar
• Fischer S , Fröhlich B , Krämer KW , et al. Relation between excitation power density and Er3+ doping yielding the highest absolute upconversion quantum yield. J Phys Chem C. 2014;118(51):30106–30114.
   Web of Science ®Google Scholar
• Xu W , Lee TK , Moon BS , et al. Broadband plasmonic antenna enhanced upconversion and its application in flexible fingerprint identification. Adv Opt Mater. 2018;6(6):1701119.
   Web of Science ®Google Scholar
• Wu DM , Garcia-Etxarri A , Salleo A , et al. Plasmon-enhanced upconversion. J Phys Chem Lett. 2014 Nov 20;5(22):4020–4031.
   PubMed Web of Science ®Google Scholar
• Eriksen EH , Madsen SP , Julsgaard B , et al. Enhanced upconversion via plasmonic near-field effects: role of the particle shape. J Opt. 2019;21(3):035004.
   Web of Science ®Google Scholar
• Saboktakin M , Ye X , Oh SJ , et al. Metal-enhanced upconversion luminescence tunable through metal nanoparticle–nanophosphor separation. ACS Nano. 2012;6(10):8758–8766.
   PubMed Web of Science ®Google Scholar
• Fischer S , Kumar D , Hallermann F , et al. Enhanced upconversion quantum yield near spherical gold nanoparticles - a comprehensive simulation based analysis. Opt Express. 2016 Mar 21;24(6):A460–75.
   PubMed Web of Science ®Google Scholar
• Shen J , Li Z , Chen Y , et al. Influence of SiO2 layer thickness on plasmon enhanced upconversion in hybrid Ag/SiO2/NaYF4: Yb, Er, Gd structures. Appl Surf Sci. 2013;270:712–717.
   Web of Science ®Google Scholar
• Xue Y , Ding C , Rong Y , et al. Tuning plasmonic enhancement of single nanocrystal upconversion luminescence by varying gold nanorod diameter. Small. 2017;13(36):1701155.
   Web of Science ®Google Scholar
• Liu X , Lei DY . Simultaneous excitation and emission enhancements in upconversion luminescence using plasmonic double-resonant gold nanorods. Sci Rep. 2015;5:15235.
   PubMed Web of Science ®Google Scholar
• Clarke C , Liu D , Wang F , et al. Large-scale dewetting assembly of gold nanoparticles for plasmonic enhanced upconversion nanoparticles. Nanoscale. 2018;10(14):6270–6276.
   PubMed Web of Science ®Google Scholar
• Fujii M , Nakano T , Imakita K , et al. Upconversion luminescence of Er and Yb codoped NaYF4 nanoparticles with metal shells. J Phys Chem C. 2013;117(2):1113–1120.
   Web of Science ®Google Scholar
• Khan M , Idriss H . Advances in plasmon‐enhanced upconversion luminescence phenomena and their possible effect on light harvesting for energy applications. Wiley Interdiscip Rev. 2017;6(6):e254.
   Google Scholar
• Liao J , Yang Z , Wu H , et al. Enhancement of the up-conversion luminescence of Yb 3+/Er 3+ or Yb 3+/Tm 3+ co-doped NaYF4 nanoparticles by photonic crystals. J Mater Chem C. 2013;1(40):6541–6546.
   Web of Science ®Google Scholar
• Yin Z , Zhu Y , Xu W , et al. Remarkable enhancement of upconversion fluorescence and confocal imaging of PMMA Opal/NaYF4: Yb 3+, Tm 3+/Er 3+ nanocrystals. Chem Comm. 2013;49(36):3781–3783.
   PubMed Web of Science ®Google Scholar
• Niu W , Su LT , Chen R , et al. 3-dimensional photonic crystal surface enhanced upconversion emission for improved near-infrared photoresponse. Nanoscale. 2014;6(2):817–824.
   PubMed Web of Science ®Google Scholar
• Hofmann CLM , Eriksen EH , Fischer S , et al. Enhanced upconversion in one-dimensional photonic crystals: a simulation-based assessment within realistic material and fabrication constraints. Opt Express. 2018 Mar 19;26(6):7537–7554.
   PubMed Web of Science ®Google Scholar
• Hofmann CL , Herter B , Fischer S , et al. Upconversion in a Bragg structure: photonic effects of a modified local density of states and irradiance on luminescence and upconversion quantum yield. Opt Express. 2016;24(13):14895–14914.
   PubMed Web of Science ®Google Scholar
• Herter B , Wolf S , Fischer S , et al. Increased upconversion quantum yield in photonic structures due to local field enhancement and modification of the local density of states–a simulation-based analysis. Opt Express. 2013;21(105):A883–A900.
   PubMed Web of Science ®Google Scholar
• Chen G , Damasco J , Qiu H , et al. Energy-cascaded upconversion in an organic dye-sensitized core/shell fluoride nanocrystal. Nano Lett. 2015;15(11):7400–7407.
   PubMed Web of Science ®Google Scholar
• Chen G , Shao W , Valiev RR , et al. Efficient broadband upconversion of near‐infrared light in dye‐sensitized core/shell nanocrystals. Adv Opt Mater. 2016;4(11):1760–1766.
   Web of Science ®Google Scholar
• Cao X , Hu B , Zhang P . High upconversion efficiency from hetero triplet–triplet annihilation in multiacceptor systems. J Phys Chem Lett. 2013;4(14):2334–2338.
   Web of Science ®Google Scholar
• Kim J-H , Deng F , Castellano FN , et al. High efficiency low-power upconverting soft materials. Chem Mater. 2012;24(12):2250–2252.
   Web of Science ®Google Scholar
• Yanai N , Kozue M , Amemori S , et al. Increased vis-to-UV upconversion performance by energy level matching between a TADF donor and high triplet energy acceptors. J Mater Chem C. 2016;4(27):6447–6451.
   Web of Science ®Google Scholar
• Wang Z , Zhao J , Di Donato M , et al. Increasing the anti-Stokes shift in TTA upconversion with photosensitizers showing red-shifted spin-allowed charge transfer absorption but a non-compromised triplet state energy level. Chem Comm. 2019;55(10):1510–1513.
   PubMed Web of Science ®Google Scholar
• Wang Z , Zhao J , Barbon A , et al. Radical-enhanced intersystem crossing in new Bodipy derivatives and application for efficient triplet–triplet annihilation upconversion. J Am Chem Soc. 2017;139(23):7831–7842.
   PubMed Web of Science ®Google Scholar
• Tao R , Zhao J , Zhong F , et al. H 2 O 2-activated triplet–triplet annihilation upconversion via modulation of the fluorescence quantum yields of the triplet acceptor and the triplet–triplet-energy-transfer efficiency. Chem Comm. 2015;51(62):12403–12406.
   PubMed Web of Science ®Google Scholar
• Okumura K , Mase K , Yanai N , et al. Employing core‐shell quantum dots as triplet sensitizers for photon upconversion. Chem–A Eur J. 2016;22(23):7721–7726.
   PubMed Web of Science ®Google Scholar
• Rautela R , Joshi NK , Novakovic S , et al. Determinants of the efficiency of photon upconversion by triplet–triplet annihilation in the solid state: zinc porphyrin derivatives in PVA. Phys Chem Chem Phys. 2017;19(34):23471–23482.
   PubMed Web of Science ®Google Scholar
• Guo H , Qin H , Chen H , et al. Phenylacetylide ligand mediated tuning of visible-light absorption, room temperature phosphorescence lifetime and triplet–triplet annihilation based up-conversion of a diimine Pt (II) bisacetylide complex. Dyes Pigm. 2013;99(3):908–915.
   Web of Science ®Google Scholar
• Singh-Rachford TN , Castellano FN . Low power visible-to-UV upconversion. J Phys Chem A. 2009;113(20):5912–5917.
   PubMed Web of Science ®Google Scholar
• Baluschev S , Yakutkin V , Miteva T , et al. Blue‐green up‐conversion: noncoherent excitation by NIR light. Angew Chem. 2007;46(40):7693–7696.
   Google Scholar
• Sun J , Wu W , Zhao J . Long‐lived room‐temperature deep‐red‐emissive intraligand triplet excited state of naphthalimide in cyclometalated IrIII complexes and its application in triplet‐triplet annihilation‐based upconversion. Chem–A Eur J. 2012;18(26):8100–8112.
   PubMed Web of Science ®Google Scholar
• Yanai N , Suzuki K , Ogawa T , et al. Absolute method to certify quantum yields of photon upconversion via triplet–triplet annihilation. J Phys Chem A. 2019;123(46):10197–10203.
   PubMed Web of Science ®Google Scholar
• Pokhrel M , Kumar Gangadharan A , Sardar DK . High upconversion quantum yield at low pump threshold in Er3+/Yb3+ doped La2O2S phosphor. Mater Lett. 2013;99:86–89.
   Web of Science ®Google Scholar
• Dyck NC , Van Veggel FC , Demopoulos GP . Size-dependent maximization of upconversion efficiency of citrate-stabilized β-phase NaYF4: Yb3+, Er3+ crystals via annealing. ACS Appl Mater Interfaces. 2013;5(22):11661–11667.
   PubMed Web of Science ®Google Scholar
• Fan S , Gao G , Sun S , et al. Absolute up-conversion quantum efficiency reaching 4% in β-NaYF 4: Yb 3+, Er 3+ micro-cylinders achieved by Li+/Na+ ion-exchange. J Mater Chem C. 2018;6(20):5453–5461.
   Web of Science ®Google Scholar
• Qin H , Wu D , Sathian J , et al. Tuning the upconversion photoluminescence lifetimes of NaYF 4: Yb 3+, Er 3+ through lanthanide Gd 3+ doping. Sci Rep. 2018;8(1):1–8.
   PubMed Web of Science ®Google Scholar
• Li X , Shen D , Yang J , et al. Successive layer-by-layer strategy for multi-shell epitaxial growth: shell thickness and doping position dependence in upconverting optical properties. Chem Mater. 2013;25(1):106–112.
   Web of Science ®Google Scholar
• Lei P , An R , Zhai X , et al. Benefits of surfactant effects on quantum efficiency enhancement and temperature sensing behavior of NaBiF 4 upconversion nanoparticles. J Mater Chem C. 2017;5(37):9659–9665.
   Web of Science ®Google Scholar
• Xue X , Uechi S , Tiwari RN , et al. Size-dependent upconversion luminescence and quenching mechanism of LiYF 4: Er 3+/Yb 3+ nanocrystals with oleate ligand adsorbed. Opt Mater Express. 2013;3(7):989–999.
   Web of Science ®Google Scholar
• Lyapin A , Gushchin S , Ermakov A , et al. Mechanisms and absolute quantum yield of upconversion luminescence of fluoride phosphors. Chin Opt Lett. 2018;16(9):091901.
   Web of Science ®Google Scholar
• Kumar G , Pokhrel M , Sardar D . Absolute quantum yield measurements in Yb/Ho doped M2O2S (M= Y, Gd, La) upconversion phosphor. Mater Lett. 2013;98:63–66.
   Web of Science ®Google Scholar
• Yang Y , Mi C , Jiao F , et al. A novel multifunctional upconversion phosphor: Yb3+/Er3+ codoped La2S3. J Am Ceram Soc. 2014;97(6):1769–1775.
   Web of Science ®Google Scholar
• Pokhrel M , Kumar G , Sardar D . Highly efficient NIR to NIR and VIS upconversion in Er 3+ and Yb 3+ doped in M 2 O 2 S (M= Gd, La, Y). ?J Mater Chem A. 2013;1(38):11595–11606.
   Web of Science ®Google Scholar
• Wang J , Ming T , Jin Z , et al. Photon energy upconversion through thermal radiation with the power efficiency reaching 16%. Nat Commun. 2014;5(1):1–9.
   Web of Science ®Google Scholar
• Grube J , Krieke G . How activator ion concentration affects spectroscopic properties on Ba4Y3F17: Er3+, Yb3+, a new perspective up-conversion material. J Lumin. 2018;203:376–384.
   Web of Science ®Google Scholar
• Xu W , Zhao H , Li Y , et al. Optical temperature sensing through the upconversion luminescence from Ho3+/Yb3+ codoped CaWO4. Sens Actuators B Chem. 2013;188:1096–1100.
   Web of Science ®Google Scholar
• Ostrowski AD , Chan EM , Gargas DJ , et al. Controlled synthesis and single-particle imaging of bright, sub-10 nm lanthanide-doped upconverting nanocrystals. ACS Nano. 2012;6(3):2686–2692.
   PubMed Web of Science ®Google Scholar
• Li X , Wang R , Zhang F , et al. Engineering homogeneous doping in single nanoparticle to enhance upconversion efficiency. Nano Lett. 2014;14(6):3634–3639.
   PubMed Web of Science ®Google Scholar
• Liu Q , Sun Y , Yang T , et al. Sub-10 nm hexagonal lanthanide-doped NaLuF4 upconversion nanocrystals for sensitive bioimaging in vivo. J Am Chem Soc. 2011 Nov 2;133(43):17122–17125.
   PubMed Web of Science ®Google Scholar
• Sivakumar S , Boyer J-C , Bovero E , et al. Up-conversion of 980 nm light into white light from sol-gel derived thin film made with new combinations of LaF 3: Ln 3+ nanoparticles. J Mater Chem. 2009;19(16):2392–2399.
   Web of Science ®Google Scholar
• Luitel HN , Chand R , Watari T . ZnMoO4: Er3+, Yb3+ phosphor with controlled morphology and enhanced upconversion through alkali ions doping. Opt Mater. 2018;78:302–311.
   Web of Science ®Google Scholar
• Wang HQ , Mačković M , Osvet A , et al. A new crystal phase molybdate Yb2Mo4O15: the synthesis and upconversion properties. Part Part Syst Charact. 2015;32(3):340–346.
   Web of Science ®Google Scholar
• MacDougall SK , Ivaturi A , Marques-Hueso J , et al. Broadband photoluminescent quantum yield optimisation of Er3+-doped β-NaYF4 for upconversion in silicon solar cells. Sol Energy Mater Sol Cells. 2014;128:18–26.
   Web of Science ®Google Scholar
• Martín-Rodríguez R , Fischer S , Ivaturi A , et al. Highly efficient IR to NIR upconversion in Gd2O2S: Er3+ for photovoltaic applications. Chem Mater. 2013;25(9):1912–1921.
   Web of Science ®Google Scholar
• Lyapin A , Ryabochkina P , Gushchin S , et al. Upconversion luminescence of fluoride phosphors SrF 2: Er, Yb under laser excitation at 1.5 μm. Opt Spectrosc. 2018;125(4):537–542.
   Web of Science ®Google Scholar
• Lyapin A , Gushchin S , Kuznetsov S , et al. Infrared-to-visible upconversion luminescence in SrF 2: Er powders upon excitation of the 4 I 13/2 level. Opt Mater Express. 2018;8(7):1863–1869.
   Web of Science ®Google Scholar
• Liu Y , Kang N , Lv J , et al. Deep photoacoustic/luminescence/magnetic resonance multimodal imaging in living subjects using high‐efficiency upconversion nanocomposites. Adv Mater. 2016;28(30):6411–6419.
   PubMed Web of Science ®Google Scholar
• Liu B , Chen Y , Li C , et al. Poly (Acrylic acid) modification of Nd3+‐sensitized upconversion nanophosphors for highly efficient UCL imaging and pH‐responsive drug delivery. Adv Funct Mater. 2015;25(29):4717–4729.
   Web of Science ®Google Scholar
• Zhang X , Chen W , Xie X , et al. Boosting luminance energy transfer efficiency in upconversion nanoparticles with an energy‐concentrating zone. Angew Chem. 2019;58(35):12117–12122.
   Google Scholar