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Yb and Er codoped NaT(XO4)2 (T = Y, La, Gd, Lu and X = Mo, W) disordered oxides show a green (Er3+ related) up-conversion (UC) efficiency comparable to that of Yb:Er:β-NaYF4 compound and unless 3 times larger UC ratiometric thermal sensitivity. The similar UC efficiency of Yb:Er doped NaT(XO4)2 and β-NaYF4 compounds allowed testing equal subcutaneous depths of ex-vivo chicken tissue in both cases. This extraordinary behavior for NaT(XO4)2 oxides with large cutoff phonon energy (ħω≈ 920 cm-1) is ascribed to 4F9/2 electron population recycling to higher energy 4G11/2 level by a phonon assisted transition. Crystalline nanoparticles of Yb:Er:NaLu(MoO4)2 have been synthesized by sol-gel with sizes most commonly in the 50–80 nm range, showing a relatively small reduction of the UC efficiency with regards to bulk materials. Fluorescence lifetime and multiphoton imaging microscopies show that these nanoparticles can be efficiently distributed to all body organs of a perfused mouse. [ABSTRACT FROM AUTHOR]

Temperature sensing by using near-infrared (λ = 976 nm)-excited upconversion (UC) of Yb, Er and Tm co-doped orthorhombic β'Gd 2 (MoO 4) 3 combines remarkable good sensitivity and thermal resolution from room temperature to 890 K, thanks to the use of three different ratiometric luminescence probes. Two of them are based on pairs of thermally coupled levels, namely 2H 11/2 →4I 15/2 vs 4S 3/2 →4I 15/2 Er3+ green emissions (R1) and deep-red 3F 3 →3H 6 vs NIR 3H 4 →3H 6 Tm3+ emissions (R3). The third one uses non-thermally coupled levels, blue 1G 4 →3H 6 vs deep-red 3F 3 →3H 6 Tm3+ emissions (R2). This multiprobe approach allows the optimization of the thermometric parameters for each selected temperature range. Based on absolute thermal sensitivity (S ABS), R1 is the best option for sensing from room temperature up to about 442 K, with R1 S ABS = 103 × 10−4 K−1 and excellent thermal resolution δT< 0.04 K at 300 K, while at higher temperatures, R2 is the most adequate probe since it combines an extraordinary increase of R2 S ABS up to 20300 × 10−4 K−1 at 776 K and very good δT< 0.2 K. When the relative thermal sensitivity (S REL) evaluation is required, R3 is the probe of choice from room temperature up to 522 K, offering simultaneously the highest R3 S REL = 3.3% K−1 and δT = 0.07 K at 300 K, with a minimum δT = 0.05 K achieved at 522 K, but R2 is still the most convenient probe for high temperature sensing, with R2 S REL = 1.6% K−1 and δT = 0.25 K. Therefore, doping β'Gd 2 (MoO 4) 3 simultaneously with Er3+ and Tm3+ provides a unique way to span the sensing temperature up to 890 K while maintaining suitable high thermal sensitivity and thermal resolution along the whole temperature range. Several favourable UC aspects specific of β'Gd 2 (MoO 4) 3 are identified as being responsible for advantages over its βNaYF 4 counterpart for high temperature sensing. [Display omitted] • High sensitivity LIR thermometry from RT to 890 K is achieved with Yb:Er:Tm:β'GMO. • Contactless thermal sensing from RT to 890 K is achieved with Yb:Er:Tm:β'GMO. • Extraordinary S ABS = 2 K−1 is achieved at high temperature by LIR thermometry with Yb:Er:Tm:β'GMO. • LIR thermometry with Yb:Er:Tm:β'GMO provides S REL = 3.3% K−1 at room temperature. [ABSTRACT FROM AUTHOR]

Tetragonal zircon-type codoped Yb, Ln–GdVO4 (Ln=Tm, Ho, Er) upconverting nanocrystals with square and rectangular sections were prepared through an efficient low-temperature hydrothermal synthesis. Further processing that combined annealing at 600 °C followed by coating of the surface with a uniform 5 nm-shell of SiO2 resulted in a significant improvement of the intensity of the upconverted emitted visible light following near-infrared (∼980 nm) diode laser excitation with respect to raw hydrothermal nanocrystals. Strong tunable color and bright visible light composed of red–green, blue and green emissions from Ho3+, Tm3+ and Er3+, respectively, were generated by adjusting the Yb–Ln composition of these silica-coated nanocrystals. Based on calculations of CIE color coordinates, nearly ideal white upconversion light was achieved for samples of composition Gd0.829Yb0.15Tm0.01Ho0.009Er0.002VO4. [ABSTRACT FROM AUTHOR]