Photoluminescence and optical temperature measurement of Mn4+/Er3+ co-activated double perovskite phosphor through site-advantageous occupation

Optimization of the structure, morphology and luminescent properties of NaYF4 upconversion nanoparticles

We designed and constructed rare earth doped upconversion nanoparticles β-Na(Y0.78Yb0.18Er0.04)F4, sensitizing layer encapsulated β-Na(Y0.9Er0.1)F4@β-NaYbF4 and inert layer encapsulated β-Na(Y0.9Er0.1)F4@β-NaYbF4@β-NaYF4. Compared with the mononuclear material, the luminescence intensity of the particles encapsulated with double shells in the three main bands of blue, green and red emissions increased by 346, 22, and 54 times respectively. While improving the upconversion luminescence performance, the underlying reasons for this improvement were analyzed in detail. The effects of shell coating on the fluorescence lifetime, thermal stability and energy level transition are discussed. On this basis, the composite film material was constructed by combining the shell coating strategy and the plasma resonance interaction strategy, which further improved the upconversion efficiency. In addition, by combining performance optimized upconversion particles with information coding, we explored its potential as an anti-counterfeiting material.

Designing dual-emission phosphors for temperature warning indication and dual-mode luminescence thermometry

Color tunable phosphors of Mn4+ and Tb3+ co-doped double-perovskite SrGdLiTeO6 (SGLT) were synthesized in this work. The crystal parameters and photoluminescence performances were investigated in detail. By taking advantage of the different thermal quenching strengths between Mn4+ and Tb3+ ions, the emission color of SGLT:0.7%Mn4+/1%Tb3+ changed from red to green, which could be used for high-temperature temperature warning indication. Moreover, according to the luminescence intensity ratio (LIR) technique, wide temperature-range optical thermometry was developed and further, the maximum relative sensitivity (SR1) value of the SGLT:0.7%Mn4+/5%Tb3+ phosphor was determined to be 1.49% K-1 at 560 K. On the other hand, the sensing properties were also analyzed based on the temperature-dependent lifetime method. The most interesting thing is that the maximum SR2 value reached 1.88% K-1 at 573 K. This work proved that the Mn4+ and Tb3+ co-doped double-perovskite SrGdLiTeO6 could be potentially used in temperature warning indication and high sensitivity luminescence thermometry.

Luminescence and energy transfer performances of Tb3+/Mn4+ co-doped Sr2LuTaO6 double-perovskite phosphors for a highly sensitive optical thermometer

A series of Tb3+/Mn4+ co-doped double-perovskite oxides Sr2LuTaO6 (SLT) phosphors are synthesized by a solid-state method. The results of structural characterization prove that the Tb3+ and Mn4+ ions are successfully doped into the SLT host. The photoluminescence excitation (PLE) and photoluminescence (PL) spectra of Sr2LuTaO6:Tb3+, Sr2LuTaO6:Mn4+ and Sr2LuTaO6:Tb3+/Mn4+ are illustrated in detail. Under ultraviolet (UV) excitation, bright green and red lights are obtained from the Sr2LuTaO6:Tb3+/Mn4+ phosphor. In particular, the emission intensity of Tb3+ ions in Sr2LuTaO6:Tb3+/Mn4+ is enhanced by the energy transfer (ET) process from Mn4+ to Tb3+. The thermal enhancement of Tb3+ ion radiation in Sr2LuTaO6:Tb3+/Mn4+ also proves the ET process (Mn4+ → Tb3+). In addition, the thermal enhancement of Tb3+ ion radiation and the thermal quenching of Mn4+ ion radiation in the Sr2LuTaO6:Tb3+/Mn4+ system can be applied to develop optical thermometry based on luminescence intensity ratio (LIR) technology. Therefore, the LIRs of Mn4+ (2Eg → 4A2g) and Tb3+ (5D4 → 7F5,4) are investigated in the temperature range from 313 to 573 K. The absolute sensitivity (Sa) and relative sensitivity (Sr) of the Sr2LuTaO6:Tb3+/Mn4+ phosphor are calculated. The maximum values of Sa and Sr are obtained from the LIR of Tb3+: 5D4 → 7F4 (570-599 nm) and Mn4+: 2Eg → 4A2g (625-705 nm). The maximum Sa is 10.18% K-1 at 543 K, and the maximum value of Sr reaches 1.98% K-1 at 543 K. These results confirm that the ET process from Mn4+ to Tb3+ contributes to increasing the temperature measuring sensitivity of the Sr2LuTaO6:Tb3+/Mn4+ phosphor. Therefore, the Sr2LuTaO6:Mn4+/Tb3+ phosphor has prospective potential in optical thermometry and provides advantageous guidance for designing high-sensitivity optical thermometers.

Improving upconversion luminescence intensity of BiTa7O19:Er3+/Yb3+ by polyvalent Sb co-doping

BiTa₇O₁₉:Er³⁺/Yb³⁺/Sb phosphors were successfully synthesized by high temperature solid sintering. X-ray diffraction (XRD), fluorescence spectrometry and X-ray photoelectron spectroscopy (XPS), were used to analyze the phase structure, upconversion luminescence (UCL) features and Sb valence state, respectively. The results suggest that polyvalent Sb with Sb³⁺ and Sb⁵⁺ can replace the Ta⁵⁺ sites in a BiTa₇O₁₉ host to form a pure phase. Compared with BiTa₇O₁₉:0.1Er³⁺/0.4Yb³⁺, polyvalent Sb doping further improves UCL intensity by 1.2 times under 980 nm laser stimulation with a powder density of 44.59 W cm^-2. This is due to the adjustment of the local lattice structure of BiTa₇O₁₉ by the polyvalent Sb. The maximum absolute sensitivity (S_A) and relative sensitivity (S_R) can be estimated from the UCL variable-temperature spectra as 0.0098 K^-1 at 356 K and 0.0078 K^-1 at 303 K using the luminescence intensity ratio (LIR) approach. The outcomes show that host local lattice adjustment using polyvalent elements is an effective way to improve luminescence intensity, and it is possible to use BiTa₇O₁₉:Er³⁺/Yb³⁺/Sb as a temperature sensor.

Multiple site occupancy induced yellow-orange emission in an Eu2+-doped KSr6Sc(SiO4)4 phosphor towards optical temperature sensors

Phosphors have attracted significant interest as potential optical temperature sensors in recent years. In our work, a new blue-light stimulated KSr₆Sc(SiO₄)₄:Eu²⁺ phosphor with decorative kröhnkite-like octahedral tetrahedral chains was successfully synthesized. Multiple site occupancy occurred in KSr₆Sc(SiO₄)₄:Eu²⁺ and induced a yellow-orange emission band with a peak at 571 nm and an FWHM of 91 nm. Gaussian fitting and time-resolved photoluminescence mapping were combined to analyze the occupation of Eu²⁺ in five Sr²⁺ sites. In the meantime, the site occupation preference, energy transfer process, and thermal quenching mechanism of Eu²⁺ emission centers have been comprehensively examined. Under 450 nm excitation, the optimal sample possesses an acceptable quantum efficiency (EQE = 17.3%) and a high sensitivity between luminescence properties and temperature variation ranging from 200 to 475 K. The optimal sample's relative sensor sensitivity achieves a maximum value of 3.53% K^-1 at 475 K. The phosphor KSr₆Sc(SiO₄)₄:0.07Eu²⁺ presents the potentiality as an optical thermometer.

Design and synthesis of a novel blue-emitting CaNaSb2O6F:Bi3+ phosphor for optical temperature sensing

Bi³⁺ has gained increasing attention due to its abundant reserves, adjustable luminous colour and high chemical stability, therefore, Bi³⁺-activated luminescent materials have already been extensively applied in various fields. Herein, a novel blue-emitting CaNaSb₂O₆F:Bi³⁺ (CNSOF:Bi³⁺) phosphor with a pyrochlore-type structure with the space group Fd3̄m (277) was successfully synthesized. It exhibits a broad absorption band in the n-UV region (290-390 nm) and an ideal blue emission band centered at 441 nm. Interestingly, the wide emission peak of CNSOF:Bi³⁺ shows strongly temperature-dependent fluorescence properties and good thermal degradation resistance in the cycle temperature range from 298 K to 473 K, and the relative sensitivity is calculated to reach the maximum value of 2.34% K^-1 at 423 K. Besides, the phosphor is different from a traditional optical temperature sensing material which shows the emission peak of trivalent rare earth ions. The wide emission peak makes the instrument insensitive to the peak shift, which dramatically reduces the requirement of the instrument, and the emission peak does not shift with the temperature to enhance the measurement stability, thus saving the cost. These results indicate that the CNSOF:Bi³⁺ blue emitting phosphor has potential applications in temperature sensing.