nanocrystals have been synthesized by hydrothermal method. The average size of obtained spheroid nanocrystals is about 35 nm. The upconversion luminescence intensity can be strengthened by adjusting alkali ions types and contents. The K
+
ions co-doped MgSc
2
O
4
:Er
3+
/Yb
3+
nanocrystals display the strongest luminescence. As K
+
content increasing
emission intensity can be enhanced gradually due to the large asymmetry of crystal field created by K
+
ions. The spectral properties of K
+
ions co-doped MgSc
2
O
4
:Er
3+
/Yb
3+
nanocrystals are described in detail as a function of Er
3+
and Yb
3+
concentrations. The MgSc
2
O
4
:1%Er
3+
/5%Yb
3+
nanocrystal was optimized for the strongest upconversion luminescence. Then
the upconversion mechanism and energy transfer processes between Yb
3+
ions and Er
3+
ions in K
+
ions co-doped MgSc
2
O
4
:Er
3+
/Yb
3+
nanocrystals were investigated under the 980 nm excitation.
HUA J T, CHEN B J, SUN J S, et al.. Introduction to up-conversion luminescence of rare earth doped materials[J].Chin. Opt., 2010, 3(4):301-309. (in Chinese)
ZHANG J H, HAO Z D, LI J, et al.. Observation of efficient population of the red-emitting state from the green state by non-multiphonon relaxation in the Er3+-Yb3+ system[J].Light:Sci. Appl., 2015, 4(1):e239.
SUN J Y, ZENG J H, SUN Y N, et al.. Synthesis and luminescence properties of novel Y2Si4N6C:Sm3+ carbonitride phosphor[J].Ceram. Int., 2013, 39(2):1097-1102.
DWIVEDI A, MISHRA K, RAI S B. Multi-modal luminescence properties of RE3+ (Tm3+, Yb3+) and Bi3+ activated GdNbO4 phosphors-upconversion, downshifting and quantum cutting for spectral conversion[J].J. Phys. D: Appl. Phys., 2015, 48(43):435103.
MAHALINGAM V, NACCACHE R, VETRONE F, et al.. Enhancing upconverted white light in Tm3+/Yb3+/Ho3+-doped GdVO4 nanocrystals via incorporation of Li+ ions[J].Opt. Express, 2012, 20(1):111-119.
RAI V K, DEY R, KUMAR K. White upconversion emission in Y2O3:Er3+-Tm3+-Yb3+ phosphor[J].Mater. Res. Bull., 2013, 48(6):2232-2236.
YU H Y, TU L P, ZHANG Y L, et al.. Quantitative analysis of the surface quenching effect of lanthanide-doped upconversion nanoparticles in solvents[J].Chin. Opt., 2019, 12(6):1288-1294. (in Chinese)
XIE W Y, AN X T, CHEN L, et al.. Tunable phase and upconverting luminescence of Gd3+ co-doped NaErF4:Yb3+ nanostructures[J].Mater. Res. Bull., 2017, 95:509-514.
LENG J, TANG J, XIE W Y, et al.. Impact of pH and urea content on size and luminescence of upconverting Y2O3:Yb, Er nanophosphors[J].Mater. Res. Bull., 2018, 100:171-177.
TANG J, CHEN L, LI J, et al.. Selectively enhanced red upconversion luminescence and phase/size manipulation via Fe3+ doping in NaYF4:Yb, Er nanocrystals[J].Nanoscale, 2015, 7(35):14752-14759.
XIANG G T, LIU X T, LIU W, et al.. Multifunctional optical thermometry based on the stark sublevels of Er3+ in CaO-Y2O3:Yb3+/Er3+ [J].J. Am. Ceram. Soc., 2020, 103(4):2540-2547.
XIANG G T, LIU X T, XIA Q, et al.. Upconversion luminescence properties of β-NaYF4:Yb3+/Er3+@β-NaYF4:Yb3+ [J].Chin. J. Lumin., 2020, 41(6):679-683. (in Chinese)
GAI S L, LI C X, YANG P P, et al.. Recent progress in rare earth micro/nanocrystals:soft chemical synthesis, luminescent properties, and biomedical applications[J].Chem. Rev., 2014, 114(4):2343-2389.
WANG D, XUE B, TU L P, et al.. enhanced dye-sensitized upconversion luminescence based on Nd3+-sensitized multi-shell nanostructures[J].Chin. Opt., doi:10.37188/CO.2020-0097.(in Chinese)
LI F, LI J, WANG Y, et al.. Impact of organic additives on synthesis and upconversion luminescence properties in Ln3+, Yb3+(Ln3+=Er3+/Tm3+/Ho3+) doped CaSc2O4 nanocrystals via hydrothermal method[J].Opt. Mater., 2019, 96:109293.
LI J, ZHANG J H, HAO Z D, et al.. Intense upconversion luminescence and origin study in Tm3+/Yb3+ codoped calcium scandate[J].Appl. Phys. Lett., 2012, 101(12):121905-1-4.
LI J, ZHANG J H, HAO Z D, et al.. Spectroscopic properties and upconversion studies in Ho3+/Yb3+ co-doped calcium scandate with spectrally pure green emission[J].ChemPhysChem, 2013, 14(18):4114-4120.
FENG L Y, HAO Z D, LUO Y S, et al.. Observation and photoluminescence properties of two Er3+ centers in CaSc2O4:Er3+, Yb3+ upconverting phosphor[J].J. Alloys Compd., 2017, 708:827-833.
CHUNG J H, LEE S Y, SHIM K B, et al.. Blue upconversion luminescence of CaMoO4:Li+/Yb3+/Tm3+ phosphors prepared by complex citrate method[J].Appl. Phys. A, 2012, 108(2):369-373.
PARCHUR A K, NINGTHOUJAM R S. Preparation, microstructure and crystal structure studies of Li+ co-doped YPO4:Eu3+[J].RSC Adv., 2012, 2(29):10854-10858.
TUO J, WANG L X, YE Y, et al.. Preparation and luminescence properties of Lu2O3:Pr3+ phosphors codoped with Li+, Na+, K+, Ca2+, Ba2+ Ions[J].Chin. J. Lumin., 2018, 39(3):307-314. (in Chinese)
LUITEL H N, CHAND R, TORIKAI T, et al.. Highly efficient NIR-NIR upconversion in potassium substituted CaMoO4:Tm3+, Yb3+ phosphor for potential biomedical applications[J].RSC Adv., 2015, 5(22):17034-17040.
MAURYA A, DWIVEDI A, BAHADUR A, et al.. Enhanced upconversion and downshifting emissions from Tm3+, Yb3+ co-doped CaZrO3 phosphor in the presence of alkali ions (Li+, Na+ and K+)[J].J. Alloys Compd., 2019, 786:457-467.
MAURYA A, BAHADUR A, DWIVEDI A, et al.. Optical properties of Er3+, Yb3+ co-doped calcium zirconate phosphor and temperature sensing efficiency:effect of alkali ions (Li+, Na+ and K+)[J].J. Phys. Chem. Solids, 2018, 119:228-237.
JIU J X, AN X T, LI J, et al.. Intense red up-conversion luminescence and dynamical processes observed in Sc2O3:Yb3+, Er3+nanostructure[J].Dalton Trans., 2017, 46(45):15954-15960.
POLLNAU M, GAMELIN D R, LVTHI S R, et al.. Power dependence of upconversion luminescence in lanthanide and transition-metal-ion systems[J].Phys. Rev. B, 2000, 61(5):3337-3346.