[1] [1] Cho S, Chen G J, Coon J. Enhancement of physical layer security with simultaneous beamforming and jamming for visible light communication systems[J]. IEEE Transactions on Information Forensics and Security, 2019, 14(10):2633-2648.

[2] [2] Chen X, Xu W, Song H W, et al. Highly efficient LiYF4∶Yb3+, Er3+ upconversion single crystal under solar cell spectrum excitation and photovoltaic application[J]. ACS Applied Materials ＆Interfaces, 2016, 8(14): 9071-9079.

[3] [3] Leleckaite A, Kareiva A, Bettentrup H, et al. Sol-gel preparation and characterization of codoped yttrium aluminium garnet powders[J]. Zeitschrift Fa~1/4 r Anorganische Und Allgemeine Chemie, 2010, 631(15):2987-2993.

[4] [4] Zhang Q, Zhang Q M. Synthesis and photoluminescent properties of α-NaYF4∶Nd/α-NaYF4 core/shell nanostructure with enhanced near infrared (NIR) emission[J]. Materials Letters, 2009, 63(3-4): 376-378.

[5] [5] Xu S, Xu W, Dong B, et al. Downconversion from visible to near infrared through multi-wavelength excitation in Er3+/Yb3+ co-doped NaYF4 nanocrystals[J]. Journal of Applied Physics, 2011, 110(11):113113.

[6] [6] Shalav A, Richards B S, Trupke T, et al. Application of NaYF4∶Er3+ up-converting phosphors for enhanced near-infrared silicon solar cell response[J]. Applied Physics Letters, 2005, 86(1):013505.

[7] [7] Chen L, Liu Y, Li Y. Preparation and characterization of ZrO2∶Eu3+ phosphors[J]. Journal of Alloys and Compounds, 2004, 381(1-2):266-271.

[8] [8] Uitert L G V, Johnson L F. Energy transfer between rare-earth ions[J]. The Journal of Chemical Physics, 1966, 44(9):3514-3522.

[9] [9] You H, Hong G. Luminescence and energy transfer phenomena of several rare earth ions in the CaAl2B2O7[J]. Materials Research Bulletin, 1997, 32(6):785-790.

[10] [10] Guo H, Dong N, Yin M, et al. Visible upconversion in rare earth ion-doped Gd2O3 nanocrystals[J]. The Journal of Physical Chemistry B, 2004, 108(50): 19205-19209.

[11] [11] Li G, Chao K, Hongrui Peng A, et al. Hydrothermal synthesis and characterization of YVO4 and YVO4∶Eu3+ nanobelts and polyhedral micron crystals[J]. Bioresource Technology, 2008, 100(14):3599-3603.

[12] [12] Yu M, Lin J, Fu J, et al. Sol-gel fabrication, patterning and photoluminescent properties of LaPO4∶Ce3+,Tb3+ nanocrystalline thin films[J]. Chemical Physics Letters, 2003, 371(1-2):178-183.

[13] [13] Chen G, Ohulchanskyy T Y, Kumar R, et al. Ultrasmall monodisperse NaYF4∶Yb3+/Tm3+ nanocrystals with enhanced near-infrared to near-infrared upconversion photoluminescence[J]. ACS Nano, 2010, 4(6):3163-3168.

[14] [14] Ma D, Meng L, Chen Y, et al. NaGdF4∶Yb3+/Er3+@NaGdF4∶Nd3+@Sodium-gluconate: multifunctional and biocompatible ultrasmall core-shell nanohybrids for UCL/MR/CT multimodal imaging[J]. ACS Applied Materials & Interfaces, 2015, 7 (30):16257.

[15] [15] Wang X, Li Y, Song Z, et al. α-NaYF4∶Nd3+ nanocrystal with near-infrared to near-infrared luminescence for bioimaging applications[J]. Journal of Nanoscience & Nanotechnology, 2014, 14(5):3910-3913.

[16] [16] And R K, Isobe T, And H K, et al. Photoluminescence enhancement of PEG-Modified YAG∶Ce3+ nanocrystal phosphor prepared by glycothermal method[J]. Journal of Physical Chemistry B, 2005, 109(47):22126-22130.