Achieving tunable multicolor display and sensitive temperature sensing in self-sensitization of erbium-doped CaF₂ nanocrystals under 808, 980 and 1532 nm irradiation

Abstract

Photon upconversion (UC) based on self-sensitization of lanthanide-doped nanocrystals is of great importance for biological and photonic applications. Here, we report tunable multicolor display and sensitive temperature sensing in the erbium-doped CaF2 upconversion nanocrystals (UCNCs) codoped with Tm3+ ions. Under the excitation of 980, 808 and 1532 nm lasers, the upconversion luminescence (UCL) color of these self-sensitized UCNCs can be manipulated from green to red efficiently and the red-to-green (R/G) UC intensity ratio is promoted remarkably as the doping Tm3+ ions vary from 0 to 4 mol%. Especially, we have successfully demonstrated the multicolor modulation of these UCNCs by changing the pulse width and repetition frequency under multi-wavelength excitation. The power dependence and decay lifetimes measurements of Er3+ ions under multi-wavelength excitation were carried out to clarify the UC color manipulation. In addition, the optical temperature sensing properties of CaF2:Er3+/Tm3+ (10/0.125 mol%) UCNCs are also studied thoroughly under 980, 808 and 1532 nm lasers excitation, and the results show that the UCNCs possess outstanding thermal sensitivity. The features enable these UCNCs to act as promising candidates for high-resolution biological imaging, multicolor display and nanoscale thermometer fields.

Lanthanide-Doped Luminescent Nanoparticles with Dual-Mode Color Modulation Enable Cross-Correlation Anticounterfeiting

“…For the abovementioned color modulation of Ln-UCNPs via the way of tuning the flux density of excitation laser, the dauntingly high power is needed in some cases for achieving desired contrast, which generally impedes its application. As an alternative to the abovementioned strategy, time-gating strategy for color modulation is based on the discrepancy in the temporal characteristic of the key cross-relaxation processes, which typically enables filtrating those luminescence features based on the relatively slow cross-relaxation upconversion process by reducing the pulse duration time of the excitation laser. ,, For the energy transfer upconversion processes crucial to the color modulation of Ln-UCNPs developed herein, namely Yb 3+ ( 5 F 5/2 ) → Er 3+ ( 4 I 11/2 ), Yb 3+ ( 5 F 5/2 ) → Tm 3+ ( 3 H 5 ), Er 3+ ( 4 I 11/2 ) → Tm 3+ ( 3 H 5 ), and Tm 3+ ( 3 H 5 ) → Er 3+ ( 4 I 13/2 ), respectively, the first one was characterized with appreciably high rate as compared to the last three due to the energy match in the former and energy mismatch in the latter cases. ,, This means that the trapping-based red luminescence emission with the involvement of the last three processes unequivocally lagged behind the green emission based on the first process, which was expected to enable temporally filtrating the red luminescence by appropriately decreasing the pulse width of the excitation laser. Taking this, we evaluated the upconversion luminescence features of the as-prepared luminescent NaGdF 4 :20%Yb, 10%Er, 0.5%Tm nanoparticles using pulsed laser as the excitation source.…”

Excitation-Power-Dependent Upconversion Luminescence Competition in Single β-NaYbF4:Er Microcrystal Pumped at 808 nm

“…The corresponding UCL transitions as well as the energy-transfer (ET) processes are also provided. The population of the Er 3+ ions can be divided into two steps: firstly, the electrons in the ground state of Er 3+ are excited to the 4 I 9/2 state by ground-state-absorption (GSA) or through ET from Yb 3+ after absorbing the 808 nm photon; then continues to reach the 2 H 9/2 state by absorbing a second 808 nm photon or 4 I 11/2 state through a non-radiative transition [ 25 ]. After that, the emitting states ( 2 H 11/2 , 4 S 3/2 , and 4 F 9/2 ) can be populated by excited-state-absorption (ESA), CR, ET, and non-radiative transition processes, which are elaborated in Fig.…”

Boltzmann- and non-Boltzmann-based thermometers in the first, second and third biological windows for the SrF2:Yb3+,Ho3+ nanocrystals under 980, 940 and 915 nm excitations

“…Therefore, accurate, fast and noninvasive measurement of the temperature is of great signi cance to practical applications. Lanthanide-doped NCs based on FIR or LIR (luminescence intensity ratio) technology could be used as luminescent thermometers which have been extensively developed recently [2][3][4][5]. The reason is that lanthanide ions have abundant energy levels and their emissions are heavily dependent on the temperature.…”