Highly Luminescent NIR-to-Visible Upconversion Thin Films and Monoliths Requiring No High-Temperature Treatment

Abstract

A method is described for producing highly luminescent composite NIR-to-visible upconversion thin films, made from β-NaYF4:3%Er,17%Yb nanocrystals in a polymethyl methacrylate (PMMA) matrix, which require no postdeposition heat treatment. Nanocrystals are synthesized via a single-phase, high-boiling-point solvent method, which requires neither metal-trifluoroacetate precursors nor the use of autoclaves. Highly luminescent films are produced that can be varied in thickness down to dimensions approaching those of the nanocrystals themselves. The physical properties of the films are characterized by AFM and TEM, whereas the spectroscopic properties are characterized by NIR-to-visible confocal microscopy and by the time-dependence of upconversion luminescence following pulsed NIR excitation. It is shown that dispersal of β-NaYF4:3%Er,17%Yb nanocrystals in PMMA has no adverse effect on the intrinsic quantum efficiency of upconversion. By focusing the NIR pump beam (980 nm, cw) in the film, linear intensity response and constant color balance are achieved at pump powers down to 40 μW. It is also demonstrated that the thin-film method can be modified to produce large NIR-to-visible upconversion monoliths of high optical quality. This study supports an earlier assertion that the upconversion properties of β-NaYF4:Er,Yb nanocrystals approach those of the bulk material when nanocrystal size is greater than ∼70 nm.

Phase angle encoded upconversion luminescent nanocrystals for multiplexing applications

“…1b) 37,38 . Such luminescence kinetics can generally fit adequately to the following equation [39][40][41] : ,…”

Preparation and characterization of upconversion luminescent NaYF4:Yb, Er (Tm)/PS bulk transparent nanocomposites through in situ polymerization

“…The strong fluorescence of nanocomposites with different b-NaYF 4 :17%Yb, 3%Er and b-NaYF 4 :25%Yb, 0.3%Tm content is probably due to the high crystallinity of the nanoparticles, which dispersed uniformly in bulk composites. The mechanism of upconversion for the Yb 3+ , Er 3+ or Yb 3+ , Tm 3+ co-doped nanocrystals has been extensively studied [23][24][25][26][27][28][29]31,64], as illustrated in Fig. 11.…”

“…Yb 3+ ions are added as sensitizer which can greatly enhance the infrared to visible upconversion efficiency due to the energy transfer from Yb 3+ to Er 3+ (or Tm 3+ ) [29]. Recently, some groups have introduced NaYF 4 :Yb 3+ , Er 3+ into polymer matrix to synthesize bulk nanocomposites [30][31][32].…”

Synthesis of β-Phase NaYF4:Yb,Er Upconversion Nanocrystals and Nanorods by Hot-Injection of Small Particles of the α-Phase

“…During the last years, a large number of research papers was pub-lished on the synthesis of NaREF 4 nanocrystals (RE = rare-earth), since NaREF 4 and LiREF 4 are attractive host lattices for a variety of functional optical materials such as upconversion phosphors, [6][7][8][9][10][11][12][13][14] quantum-cutting phosphors, [15][16][17][18][19] laser materials, [20,21] and materials for solar cell applications [22][23][24][25][26]. A variety of synthetic methods has been described for producing solvent-dispersible sodium rare-earth tetrafluoride nanocrystals with controlled size, shape and capping ligand, including thermal decomposition, [7,[27][28][29][30][31][32] co-precipitation, [6,11,[33][34][35][36][37][38][39][40] or solvothermal methods [41][42][43][44][45][46][47]…”