Enhanced upconversion emission of Er3+/Yb3+ and Er3+/Yb3+/Zn2+ doped calcium aluminate for use in optical thermometry and laser induced optical heating

Intense photoluminescence in CaTiO3:Sm3+ phosphors, effect of co-doping singly, doubly and triply ionized elements and their applications in LEDs

In this work, Sm³⁺-doped and Sm³⁺/Li⁺/K⁺/Mg²⁺/Ba²⁺/Gd³⁺/Bi³⁺ co-doped CaTiO₃ phosphors were synthesized by a solid-state reaction method at 1473 K. The phase of phosphors was identified to be orthorhombic with space group Pnma (62) by XRD measurements. The morphological properties of the prepared samples were studied by SEM measurements. The average crystallite and particle sizes were found to increase in the presence of modifiers and they follow the trend Li⁺ > Mg²⁺ > Gd³⁺ > K⁺ > Bi³⁺ > Ba²⁺. EDX measurements were used to verify the presence of Ca, Ti, O, Sm, K, Mg, Ba, Gd and Bi atoms in the prepared phosphor samples. The Sm³⁺ ion shows emission peaks at 564, 599 and 646 nm due to ⁴G_5/2 → ⁶H_5/2, ⁶H_7/2 and ⁶H_9/2 transitions upon 407 nm excitation, among which the peak situated at 599 nm has maximum emission intensity. Concentration quenching was observed above 2 mol% of Sm³⁺ ions in this host. However, the emission intensity of Sm³⁺ peaks can be enhanced using different modifier (Li⁺/K⁺/Mg²⁺/Ba²⁺/Gd³⁺/Bi³⁺) ions. It was found that the size (ionic radii) and charge compensation of the ion together play a dominant role. The enhancement is more after co-doping with smaller radius ions (Li⁺, Mg²⁺ and Gd³⁺), among which Li⁺ shows the largest enhancement. This is because ions of smaller size will be able to go closer to the activator ion and the charge imbalance causes a larger field. The CIE color coordinates, correlated color temperature (CCT) and color purity of the phosphors were calculated and show orange-red color emissions with a maximum color purity of ∼93% in the case of CaTiO₃:2Sm³⁺/1.0Li⁺ phosphor. The lifetime value is increased in the presence of these ions. It is again maximum for the Li⁺ co-doped CaTiO₃:2Sm³⁺ phosphor sample. Thus, the prepared phosphor samples are suitable sources for orange-red light.

Enhancing the temperature sensing property of a Ca0.79-xBixEr0.01Yb0.2MoO4 phosphor via local symmetry distortion and reduction in non-radiative channels

We demonstrate an enhancement in the upconversion (UC) emission and temperature sensing property of a CaMoO4:Er/Yb phosphor via distortion of the local symmetry environments and reduction in no-radiative channels. Bi3+ ion co-doping creates a local distortion while the average tetragonal structure of CaMoO4 remains intact. This creates asymmetry around the Er3+ ions which improves the UC emission. Furthermore, our calculations on XRD data show a reduction in the dislocation density and the micro-strain in the crystal with the introduction of Bi3+, which also favours the enhancement of UC emission as it reduces the non-radiative channels. Furthermore, the effect of this enhancement on the temperature sensing property of Er3+ ion has also been revealed. Our results show that the UC emission is enhanced about 25 times for Bi3+ co-doped samples which improves the temperature sensitivity significantly. The samples, both with and without Bi3+ co-doping, exhibited relative sensitivities of 0.0068 K-1 at 300 K and 0.0057 K-1 at 298 K which is a significant improvement and indicates the potential of the material for temperature sensing applications. This proof-of-concept provides a deeper understanding of the effect of Bi3+ doping on UC emission and opens new avenues for the development of high-performance temperature sensing materials.

Photoluminescence behavior of Eu3+ doped XAl2O4(X = Mg, Ca, Sr and Ba) phosphors: a comparative study

In this work, the Eu³⁺doped stuffed tridymite type structure of alkaline earths aluminate i.e. XAl₂O₄(X = Mg, Ca, Sr and Ba) phosphor materials have been synthesized by conventional high temperature solid state reaction method at 1623 K. The Samples were structurally and morphologically characterized by x-ray diffraction (XRD) and Scanning electron microscope (SEM) measurements. The vibrational behavior of the phosphor samples were investigated by Fourier transform infrared (FTIR) measurements. The phosphor samples emit intense red emission in 610-615 nm range due to⁵D₀ → ⁷F₂transition of Eu³⁺ion on excitation with charge transfer band (CTB) wavelength arising due to Eu³⁺-O^2-and also by the discrete bands of Eu³⁺ions .The decay time of⁵D₀level of Eu³⁺ion were recorded on excitation with 393 nm and by the CTB wavelength for all the four samples. The optimized 1 mol% Eu³⁺doped CaAl₂O₄phosphor exhibits optimum emission intensity and color purity under the excitation with 393 nm than others. The decay time is also found to be larger in the case of Eu³⁺doped CaAl₂O₄phosphor sample. Therefore, Eu³⁺doped CaAl₂O₄phosphor may be promising material for red color light emitting applications and white light generation.

A sensitive near infrared to near-infrared luminescence nanothermometer based on triple doped Ln -Y2O3

In recent years, luminescence nanothermometers with near infrared light (NIR) emission excited in the NIR range have attracted much attention due to their potential in bio applications. Here, we propose a new nanothermometer based on triple doped 1%Ho, 1%Er, 1%Yb - Y₂O₃ that operates in the second and third biological windows around 1200 and 1530 nm under pulsed excitation at 905 nm. The NIR emissions were analysed in the temperature range of 298-473 K in terms of intensity, shape and dynamics. The nanothermometer performances were described using the luminescent intensity ratio (LIR) corresponding to the ⁵I₆-⁵I₈ and ⁴I_13/2-⁴I_15/2 emissions transitions of Ho and Er, respectively. A maximum relative sensitivity of 1.5% K^-1 was achieved at 309 K, which is among the highest five values reported so far for the NIR to NIR downconversion nanothermometers. The thermometer performance for biological application was assessed in terms of nanothermometer reliability and stability as well as emission shape changes induced by water and custom designed optical phantoms. Combination between use of pulsed excitation and identification of Ln doping configuration offering both excitation and emission in the biological windows represent a solid approach that can be easily translated to other hosts to develop a new class of near infrared nanothermometers.

Anti-escaping of incident laser in rare-earth doped fluoride ceramics with glass forming layer

Adaptive fluoride ceramic with glass forming layer (GC_ZBL-Er) used in laser anti-escaping has been prepared by one-step synthesis, and the thickness of glass layer is identified as ~0.41 mm. Blue, green and red emissions of Er³⁺/Yb³⁺ codoped fluoride ceramic (C_ZBL-Er) and glass layer (G_ZBL-Er) have been investigated under ~980 nm laser pumping. With the forming of thin glass layer on ceramic surface, the absorption intensities on diffuse reflection of GC_ZBL-Er at 974 nm and 1.53 μm increase by 48% and 53% than those of C_ZBL-Er. Excited by a 979 nm laser, the presence of the glass layer increases the absolute absorption rate in spectral power from 75% in C_ZBL-Er to 83% in GC_ZBL-Er, which is consistent with the improvement in the absorbed photon number. In addition, the quantum yield of GC_ZBL-Er complex is raised by 28.4% compared to the case of ceramic substrate by photon quantification. Intense absorption-conversion ability and efficient macroscopical anti-escaping effect confirm the superiority of ingenious structure in the fluoride ceramics with glass forming layer, which provides a new approach for developing the absorption-conversion materials of anti-NIR laser detection.