Understanding the effect of Mn2+ on Yb3+/Er3+ co-doped NaYF4 upconversion and obtaining the optimal combination of these tridoping

Abstract

In this work, we investigated in detail the upconversion properties of several types of nanoparticles, including NaYF₄:5%Yb³⁺/30%Mn²⁺, NaYF₄:40%Mn²⁺/x%Yb³⁺ (x% = 1, 5, 10, 20, 30, and 40), NaYF₄:2%Er³⁺/x%Mn²⁺ (x% = 20, 30, 40, 50, 60, and 70), NaYF₄:40%Mn²⁺/x%Er³⁺ (x% = 1, 2, 5, and 10), and NaYF₄:40%Mn²⁺/1%Yb³⁺/x%Er³⁺ (x% = 0, 2, 5, and 10). We studied their upconversion emission under 980 nm excitation in both pulsed and continuous wave modes at different synthesis temperatures. The nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and photoluminescence (PL) spectroscopy. The doping of Yb³⁺ and Mn²⁺ ions resulted in the nanoparticles assuming cubic and hexagonal crystal structures. The emission intensity increased (106.4 (a.u.*10³) to 334.4(a.u.*10³)) with increasing synthesis temperature from 120 to 140 °C, while a sharp decrease was observed when the synthesis temperature was increased to 200 °C. The gradual decrease in peak intensity with increasing Mn²⁺ concentration from 20 to 70% was attributed to energy transfer from Mn²⁺ to Yb³⁺. In NaYF₄:Mn²⁺/Yb³⁺/Er³⁺ UCNPs, increasing the Er³⁺ concentration from 0 to 10% led to the disappearance of the blue, orange, and green emission bands. The intense upconversion luminescence pattern with high spatial resolution indicates excellent potential for applications in displays, biological sensors, photodetectors, and solar energy converters.

Figure 1

TEM images of the as-synthesized (a) NaYF4, (b) 30%Mn 5%Yb 120 °C, (c) 30%Mn 5%Yb 140 °C, (d) 30%Mn 5%Yb 160 °C, (e) 30%Mn 5%Yb 180 °C, and (f) 30%Mn 5%Yb 200 °C. The analyzed samples were in solution form.

Figure 2

TEM images of NaYF4: Mn²⁺, Yb³⁺ nanocrystals doped with (a) 30%, (b) 40%, (c) 50%, (d) 60% and (d) 70% Mn²⁺ ions. The analyzed samples were in solution form.

Figure 3

XRD patterns of (a) NaYF₄: 5%Yb³⁺/30%Mn²⁺ UCNPs at different synthesis temperatures (120 °C, 140 °C, 160 °C, 180 °C, 200 °C), (b) NaYF4: 5%Yb³⁺/x%Mn²⁺ (x% = 30, 40, 50, 60, 70%) UCNPs, (c) NaYF4 UCNPs at different Yb³⁺ concentration (NaYF4:40%Mn²⁺ /1%Yb³⁺ and NaYF4:40%Mn²⁺ /40%Yb³⁺). The analyzed samples were in solution form.

Figure 4

XRD patterns of NaYF₄, NaYF₄:1%Yb³⁺/40%Mn²⁺/2%Er³⁺ and NaYF₄:1%Yb³⁺/40%Mn²⁺/10% Er³⁺ UCNPs. The analyzed samples were in solution form.

Figure 5

(a) UCL emission spectra of NaYF₄:5%Yb³⁺/30%Mn²⁺ nanoparticles with different synthesis temperatures (120 °C, 140 °C, 160 °C, 180 °C and 200 °C) and (b) log intensity versus synthesis temperature under 980 nm CW excitation. (c) UCL emission spectra of NaYF₄:5%Yb³⁺/x%Mn²⁺ (x% = 20, 30, 40, 50, 60 and 70%) nanoparticles and (d) log intensity versus Mn²⁺ concentration under 980 nm CW excitation. (e) UCL emission spectra of NaYF₄:40% Mn²⁺/x%Yb³⁺ (x% = 1, 5, 10, 20, 30 and 40%) nanoparticles and (f) log intensity versus Yb³⁺ concentration under 980 nm CW excitation. The pulse duration for the impact mode was 3 min, the power density of the 980 nm laser was 1 W/cm², and the spot width was 3 mm. 1000 µl of the solution was poured into the cuvette and the cuvette was placed inside the measuring device.

Figure 6

(a) Lifetimes spectra of NaYF₄:5%Yb³⁺/30%Mn²⁺ nanoparticles with different synthesis temperatures (120 °C, 140 °C, 160 °C, 180 °C and 200 °C) and (b) amount of decay under 980 nm pulsed excitation. (c) Lifetimes spectra of NaYF₄:5%Yb³⁺/x%Mn²⁺ (x% = 20,30, 40, 50, 60 and 70) nanoparticles, (d) amount of decay under 980 nm pulsed excitation. (e) Lifetimes spectra of NaYF₄:40% Mn²⁺/x%Yb³⁺ (x% = 1, 5, 10, 20, 30 and 40) nanoparticles, (f) amount of decay under 980 nm pulsed excitation. The power density and spot diameter of the used 980-nm laser are 10 W/cm² and 3.0 mm, respectively. Luminescence decay times were measured in the red wavelength region. The analyzed samples were in solution form.

Figure 7

(a) UCL emission spectra of NaYF₄: 40% Mn²⁺/x%Er³⁺ (x% = 1, 2, 5 and 10) nanoparticles and (b) log intensity versus Er³⁺ concentration under 980 nm CW excitation. (c) UCL emission spectra of NaYF₄: 2% Er³⁺/x%Mn²⁺ (x% = 20, 30, 40, 50, 60 and 70) nanoparticles (d) log intensity versus Mn²⁺ concentration under 980 nm CW excitation. (e) UCL emission spectra of NaYF₄: 1% Yb³⁺/40% Mn²⁺/x%Er³⁺ (x% = 0, 2, 5, and 10) nanoparticles (f) log intensity versus Er³⁺ concentration under 980 nm CW excitation. NaYF₄:Yb³⁺/Mn²⁺ nanoparticles emitted relatively strong emission band at 575 nm. The pulse duration for the impact mode was 3 min, the power density of the 980 nm laser was 1 W/cm², and the spot width was 3 mm. 1000 µl of the solution was poured into the cuvette and the cuvette was placed inside the measuring device.

Figure 8

(a) Schematic of energy level diagrams of NaYF4:Yb³⁺ /Mn²⁺/Er³⁺ and the proposed mechanism of the UC process under the excitation of 980 nm. (b) Schematic of energy level diagrams of Mn²⁺–Yb³⁺ dimer.

Figure 9

(a) Lifetimes spectra of NaYF₄: 1% Yb³⁺/40% Mn²⁺/x%Er³⁺ (x% = 0, 2, 5, and 10) nanoparticles, (b) amount of decay under 980 nm pulsed excitation. The power density and spot diameter of the used 980-nm laser are 10 W/cm² and 3.0 mm, respectively. Luminescence decay times were measured in the red wavelength region. The analyzed samples were in solution form.