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A packaged low-loss Er3+-doped silicate glass microsphere laser is demonstrated, whose temperature sensing characteristics at different pump wavelengths are studied comparatively. An active microsphere with ultrahigh Q -factor beyond 107 is prepared by an optimized material scheme with decreased compositions and an improved arc-discharge method. The microsphere can excite lasing in 1550 nm band under both 980 and 1480 nm pumping with low threshold powers of ∼96 and ∼148 μW, respectively. Furthermore, a simple and efficient method is utilized to package the microsphere laser for enhancing the stability of laser emission. The movable device can be applied for temperature sensing with high sensitivities of 18.82 and 19.86 p.m./°C under 980 and 1480 nm pumping, respectively. And the measurable temperature range is 15 °C wider under 980 nm pumping compared with 1480 nm pumping, which is due to the higher fluorescence intensity resulting from the quicker population inversion under 980 nm pumping. The packaged microsphere device has great potential for lasing and temperature sensing applications, with the advantages of enhanced robustness and high temperature sensitivity. The following are the highlights of the packaged Er3+-doped silicate glass microsphere laser temperature sensor in our work. • Modified composition and fabrication are used to enhance Q-factor of microcavity. • Simple and efficient method is used to package the microsphere laser for sensing. • Wider measurable temperature range for 980 nm pumping is explained theoretically. [ABSTRACT FROM AUTHOR]

Novel Ca 2 MgWO 6 phosphors doped with xEr3+ (x = 0.5, 1, 2, 3, and 4 mol%) were synthesized using the solid-state reaction method. Using XRD and FTIR analyses, successful product formation was confirmed. Subsequently, the phosphor was optimized by focusing on the characteristic emission peak at 529 nm, arising from the transition 2H 11/2 → 4I 15/2. The optimal concentration of Er³⁺ for the given host system was determined to be 2 mol%. Meticulous analyses revealed that the optimized phosphor possessed a direct optical band gap of 3.68 eV and the bonding parameter confirmed that the nature of bonding was ionic nature between the dopant and the host. Furthermore, phosphor also demonstrated high thermal stability up to 500 °C, excellent thermal quenching temperature of 357.43 K, and anomalous temperature-dependent emission properties. All these incredible features make the prepared phosphor a promising candidate for multifield applications like light generation, temperature sensing, etc. [Display omitted] • Er3+ doped Ca 2 MgWO 6 phosphors has been successfully synthesized through solid-state reaction method. • XRD and FTIR revealed that the structural properties were of the phosphor was not affetcted by the doping. • Prepared phosphor exhibited greenish emission and an abnormal TDPL spectra and great thermal stability. • The phosphor's unique features make it ideal for light emission, WLED, and thermal sensing applications. [ABSTRACT FROM AUTHOR]

In recent years, upconversion (UC) luminescence has gained attention due to its unique optical properties, and the thermal response spectral characteristics of these materials have been widely utilized in various fields including temperature sensing and biomedical research. However, the photoluminescence (PL) intensity of most rare earth ions doped phosphors decreases with increasing temperature, and the visible fluorescence emission penetration is still limited. In the work, the pure phase of Yb3+ and Er3+ ions co-doped Sc 2 Mo 3 O 12 was successfully prepared. The Sc 2 Mo 3 O 12 : Yb3+, Er3+ sample showed a single emission of UC near-infrared (NIR) light. The optimum doping concentrations of 0.2 for Yb3+ ions and 0.01 for Er3+ ions were achieved. The possible upconversion luminescence (UCL) mechanism was investigated by analysing the UCL spectra, the down-shift (DS) excitation and emission spectra of Sc 2 Mo 3 O 12 : Yb3+, Er3+ phosphor. The excitation path of NIR emission is mainly through Er3+ from 2H 11/2 to 4I 9/2 energy level. What's more, the temperature-dependent near-infrared UCL properties of sample is explored in the temperature range from 323 K to 673 K. The enhancement of upconversion luminescence intensity shows a linear relationship with increasing temperature. The study paves a new way for non-contact optical temperature measurement with single near-infrared UCL emission. • The Sc 2 Mo 3 O 12 :Yb3+/Er3+ with a single near-infrared emission was prepared. • The optimal doping of Sc 2 Mo 3 O 12 :Yb3+/Er3+ phosphor is 0.2 Yb3+/0.01Er3+, respectively. • The single upconversion near-infrared emission mechanism of new phosphor is confirmed. • Single near-infrared light from Sc 2 Mo 3 O 12 :Yb3+/Er3+ phosphor for temperature detection. [ABSTRACT FROM AUTHOR]

The novel orange-red emitting K 5 Y(MoO 4) 4 : x Sm3+ (KYMO: x Sm3+) (1 mol% ≤ x ≤ 35 mol%) phosphors were synthesized through solid-phase reaction. The KYMO:Sm3+ phosphors were mainly analyzed for purity phase, luminescence properties, and thermostability. Under 403 nm excitation, KYMO:10 mol%Sm3+ possesses four distinct emission peaks. The dominant emission peak is situated at 645 nm, corresponding to the 4G 5/2 → 6H 7/2 electron transitions. With x = 10 mol%, the KYMO: x Sm3+ phosphor has the optimal doping concentration. The color purity reaches as high as 99.9 %. KYMO:10 mol%Sm3+ presents good thermostability with T 0.5 > 480 K and resistance to color drift (Δ E = 0.012 at 420 K). The lifetime for KYMO:10 mol%Sm3+ is 1.16 ms. The internal quantum efficiency (IQE) reaches 62.74 %. At 480 K, the maximum temperature sensing sensitivities of the FIR of I 564 /I 599 are 5.19 × 10−4 (S a) and 18 % (S r). The assembled WLED displays an excellent color rendering index (CRI, R a) of 94, Commission International de L′ Eclairage (CIE) coordinates (0.333, 0.346), and a correlated color temperature (CCT) of 5464 K. In summary, KYMO:Sm3+ phosphors possess great promise for high CRI white-light-emitting diodes (WLEDs) and potential feasibility for temperature sensing. • K 5 Y(MoO 4) 4 :Sm3+ phosphors have been synthesized via solid-state reaction firstly. • The phosphor emits bright orange-red light excited by 403 nm. • The synthesized phosphors exhibit the superior color purity (99.8 %–99.9 %). • The fabricated WLED exhibits a high color rendering index (R a = 94). [ABSTRACT FROM AUTHOR]

The Lu 2 O 2 S exhibits exceptional properties in terms of its high density, chemical stability, and optical inertia as a luminescent matrix material, however, the preparation process poses significant challenges. Herein, solid phase synthesis was improved to prepare Lu 2 O 2 S: Er3+/Yb3+ phosphors with high crystallinity and homogenous particle size without agglomeration. The phosphor continuously emits bright green light under the excitation of a near-infrared 980 nm laser, which is not affected by the laser power, doping concentration and temperature. The optical thermal sensing performance of the phosphor using LIR (Luminescence intensity ratio) method was carried out, the Sr (relative sensitivity of temperature) is rather high with reaching a maximal value of 0.99 % K−1 at 363 K, indicating Lu 2 O 2 S:Er3+/Yb3+ up-conversion phosphor has good temperature sensing behavior. Furthermore, through spectral overlap and luminescence decay lifetime, the energy transfer mechanism was inferred to be a quadrupole-quadrupole interaction. This work suggests that Lu 2 O 2 S:Er3+/Yb3+ phosphor could be a candidate for non-contact nanothermometers, anti-counterfeit and biological imaging. • The Lu 2 O 2 S: Er3+/Yb3+ up-conversion phosphor was prepared by improved solid-state sintering, by which high crystallinity and uniform particles without agglomeration could be successfully prepared. • The composition was optimized to be Lu 2 O 2 S with doping of 3 % Yb3+ and 0.5 % Er3+ with strongest green light. • The optical thermal sensing performance of the phosphor using luminescence intensity ratio method was also carried out, the relative sensitivity of temperature is rather high with reaching a maximal value of 0.99 % K−1 at 363 K, it is expected to be a good candidate for non-contact thermometers. • The mechanism of energy transfer between doping ions was inferred to be a quadrupole-quadrupole interaction according to the spectral and decay time analysis. [ABSTRACT FROM AUTHOR]

Fluorescent temperature sensing materials are generally designed based on the phenomenon that the fluorescence intensity ratio (FIR) of luminescence at different wavelength positions changes linearly with temperature. Luminescence at different wavelength positions can come from two different luminescent centers. The key to the design of such materials is that the two luminescent centers have different degrees of change with temperature, that is, they have different thermal quenching behavior. Herein, we have investigated the luminescence properties and structure of Eu3+ and Mn4+ co-doped in Sr 2 InTaO 6. The emission of doped Eu3+ (rare earth) changes little with the increase of temperature. However, the emission of doped Mn4+ (transition metal) decreases sharply with increasing temperature. Materials in two different temperature ranges (80–300 K under room temperature, and 300–523 K above the room temperature) have shown a satisfactory temperature sensing performance. This work points out a direction for the design of temperature sensing materials based on the FIR of two luminescent centers, that is, mixing an ion with excellent luminescence thermal stability (such as rare earth ion Eu3+, Sm3+, Dy3+, etc.) as a reference, and an ion with relatively poor luminescence thermal stability (such as transition metal Mn4+, main group element ion Bi3+, etc.) as the temperature scale. • A series of Sr 2 InTaO 6 : x Eu3+, 0.005Mn4+ phosphors were synthesized by conventional high-temperature solid-phase reaction. • The FIR was used to design fluorescent temperature sensing materials with linear change of temperature. • As the temperature increases, the emission intensity of Eu3+ (5D 0.→7F 2) and Mn4+ (2E g →4A 2g) decreased to different degrees, that is, the sensitivity of Eu3+ and Mn4+ to temperature are different. • The temperature sensing properties of Sr 2 InTaO 6 : 0.06Eu3+, 0.005Mn4+ phosphor were studied at 80–300 K and 298–523 K. • The equation was used to fit FIR and temperature, and S a and S r were calculated. S a = 0.056 K−1 at 80 K, S r = 0.72 %K−1 at 240 K, S a = 0.068 K−1 at 298 K, S r = 1.38 %K−1 at 398 K. [ABSTRACT FROM AUTHOR]

The development of up-conversion materials with strong emission and low thermal effect is crucial for achieving higher temperature sensing accuracy. In this work, novel transparent NaLu 2 F 7 : x Yb3+, 0.02Er3+ (x = 0, 0.2, 0.4, 0.6, 0.8, 1) glass-ceramics (GCs) were manufactured by melt-quenching technique. The temperature sensing capabilities of GC20 based on thermally coupled energy levels (TCELs) and non-thermally coupled energy levels (nTCELs) were studied, which enable self-calibration. Our findings reveal that the maximum relative sensitivity (S Rmax) of TCELs and nTCELs are 1.19% K−1 and 0.89% K−1 at 313 K, respectively. More importantly, the UC luminescence color of GC20 varies from yellow to green as the excitation power increases. The unique phenomenon can be utilized for anti-counterfeiting purposes without any background interference. Overall, our results demonstrate that these novel GCs possess significant potential in accurate temperature sensing and anti-counterfeiting fields. • The transparent NaLu 2 F 7 :Yb3+, Er3+ glass-ceramics are successfully elaborated. • The self-calibration temperature sensing based on TCELs and nTCELs is achieved. • Heating effect is erased by optimizing concentration of Yb3+ and excitation power. • By varying excitation power of 980 nm laser, tunable emission can be achieved. [ABSTRACT FROM AUTHOR]

Rare earth doped fluoride-based up-conversion luminescent materials have been widely studied in non-contact temperature sensing technology. However, the luminous intensity of the fluoride at high temperature still needs to be improved. Here, enhanced up-conversion luminescence and temperature sensing performance of NaBiF 4 : Er3+, Yb3+ is realized by Al3+ substitution. The samples exhibit the characteristic green (521 nm and 540 nm) and red (654 nm) emissions of Er3+ ion under 980 nm excitation. When the concentration of Al3+ is 5%, the green emission is enhanced by about 10 times, and the red light is enhanced by about 7 times. Obvious lattice shrinkage caused by the introduction of Al3+ is responsible for the enhancement. In addition, the optimal sample is highly thermally stable from 303 K to 443 K. The maximum relative sensitivity at 303 K increases from 0.791% K−1 to 1.106% K−1. The results indicate that NaBiF 4 : Er3+, Yb3+, Al3+ be a potential thermosensitive material. • Enhanced up-conversion luminescence and temperature sensing of NaBiF 4 : Er3+, Yb3+ is realized by Al3+ substitution. • Obvious lattice shrinkage caused by the introduction of Al3+ is responsible for the enhancement. • The optimized sample is highly thermally stable from 303 K to 443 K. • The maximum relative sensitivity is up to 1.106% K−1 at 303 K. [ABSTRACT FROM AUTHOR]

Up to now, the research field of application of lanthanide ions doped lead-free double perovskite Cs 2 AgInCl 6 nanocrystals (NCs) was relatively limited, even less in temperature sensing. Here, Tb3+/Ho3+/Bi3+ ions were successfully doped into Cs 2 AgInCl 6 NCs by hot-injection. The temperature sensing performance of co-doped NCs by using the fluorescence intensity ratio (FIR) was studied through the temperature-dependent emission spectra. By analyzing the influence of ions' doping concentration on temperature sensing performance, the optimal doping concentration of co-doped Cs 2 AgInCl 6 NCs was determined to be 7 % Tb3+, 20 % Ho3+ and 1 % Bi3+. The highest absolute and relative sensitivities reach 1.48 K−1 and 2.48 %/K, respectively. We provide a new doping scheme of lead-free double perovskite NCs which have good temperature sensing performance. This co-doped NCs have great potential application value in non-contact temperature sensing in nanoscale. • Novel Tb3+/Ho3+/Bi3+ co-doped perovskite Cs 2 AgInCl 6 nanocrystals were manufactured. • Temperature sensing is based on fluorescence intensity ratio between Ho3+ and Tb3+. • Maximum absolute and relative sensitivities reach 1.48 K−1 and 2.48 %/K, respectively. [ABSTRACT FROM AUTHOR]

Optical thermometry achieved by luminescent materials with good stability and high sensitivity has attracted much attention. In this article, Ba 3 Y 2 B 4 O 12 , a borate with good chemical stability and high laser threshold was chosen to be host material for preparing a series of Ba 3 Y 2-x-y Yb x Ho y B 4 O 12 (BYBO:xYb3+/yHo3+; 0.01 ≤ x ≤ 0.35, 0.005 ≤ y ≤ 0.035) upconversion phosphors by a facile solid-state method. Under 980 nm excitation, phosphors show strong 551 nm green emission, weak 668 nm red emission, and 755 nm near-infrared emission, while bright greenlight can be observed by naked eye. When x = 0.15, y = 0.01, luminescent intensity obtains the maximum value. At higher doping concentration, the reduction of cell parameters caused by doping can accelerate the decrease of distance between dopants, so that the energy back transfer process is more likely to occur, weakening the green emission. The intensified non-radiative relaxation results in an increased red emission proportion at higher temperature. According to this rule, the temperature sensing properties based on the fluorescence intensity ratio I 668 /I 551 and I 688 /I 755 are studied. The maximum relative sensitivity (S R) reaches 1.53 % K−1 at 478 K, which is higher than most of reported materials. It shows that BYBO:Yb3+/Ho3+ has application potential in temperature sensing. • The upconversion luminescence was achieved in Ba 3 Y 2 B 4 O 12 for the first time. • Temperature sensing properties based on FIRs I 668 /I 551 and I 668 /I 755 are studied. • The maximum relative sensitivity (S R) reaches a value of 1.53 % K−1. [ABSTRACT FROM AUTHOR]

Rare-earth-based double perovskites exhibit excellent thermal, water, and oxygen stability, making them promising environmentally friendly materials for various applications such as anti-counterfeiting, LED technology, infrared imaging, and photodetectors. In this study, we utilized the hot injection method to prepare Cs 2 NaYbCl 6 :Er3+/Bi3+/Sb3+ double perovskite nanocrystals, realizing upconversion visible and downshifting NIR emission under 980 nm and 1550 nm excitation, and their luminescence and dynamics as a function of temperature were further investigated. The luminescence intensity of Er3+ in Cs 2 NaYb 0.85 Er 0.15 Cl 6 can be improved by Sb3+ or Bi3+ doping, and they exhibited the temperature dependent visible and NIR emission with an optimum temperature around 100–130 K. Furthermore, the intensity ratios of R H/S and R r/g increase consistently with temperature in the range of 80–310 K. The temperature sensing sensitivity of Cs 2 NaYb 0.845 Er 0.15 Sb 0.005 Cl 6 at 310 K increases from 2.39 % K−1 to the relative sensitivity (S R) of 2.90 % K−1 for Cs 2 NaYb 0.85 Er 0.15 Cl 6. Our work providing a detailed understanding on the luminescent performance of perovskites through transition metal doping, expanding their temperature sensing application. • We utilized the hot injection method to prepare Cs 2 NaYbCl 6 :Er3+/Bi3+/Sb3+ double perovskite nanocrystals, and Bi3+ and Sb3+ were doped into the samples to enhance the luminescence performance. • Temperature dependence of luminescence and dynamics demonstrates that Cs 2 NaYbCl 6 :Er3+, and Cs 2 NaYbCl 6 :Er3+/Sb3+ double perovskites with the increase of temperature, the luminescent intensities for the UC visible and downshifting NIR emission first enhance and then weaken. • They originate from the enhanced cross-section of sensitizer Yb3+ or intensified non-radiative rates. • In addition, we have achieved a high sensitivity measurement under 980 nm excitation, with the highest S R being 11.21 % K−1 at 80 K. [ABSTRACT FROM AUTHOR]

On the basis of BiTa 7 O 19 (BTO):0.1Er3+/0.4 Yb3+, Zn2+, S2−, Mo4+ and V5+ single doped upconversion phosphors (UCP) were successfully prepared by solid phase sintering. The lattice structure, particle size and diffuse reflectance spectra were measured by X-ray diffraction, scanning electron microscope and spectrophotometer. Upconversion luminescence (UCL) spectra of these UCP were investigated under 980 nm laser excitation with power density from 1.82 to 124.99 W/cm2. Zn2+ doped UCP can obtain the highest UCL intensity when excitation power density is less than 56.91 W/cm2, and Mo4+ doped UCP can obtain the highest UCL intensity when excitation power density is from 56.91 to 124.99 W/cm2. The UCL intensity of all samples increases first and then decreases with the increase of excitation power. By measuring UCL intensity changes with the excitation power of the UCP mixing with BN and UCP in vacuum and atmosphere, the experimental results show that the increase of temperature caused by laser excitation is the reason for the decrease of UCL intensity under high power excitation. Utilizing LIR technology, it is proven that at high power 90.95 W/cm2, Mo4+ and Zn2+ single doped can decrease and increase the UCP temperature under the same power density excitation compared with BTO:0.1Er3+/0.4 Yb3+, respectively. The maximum relative temperature sensitivity of all UCP is calculated in the range of 0.00767–0.00854 K−1 at 303 K. All experiments show that Zn2+ and Mo4+ single-doped UCP are suitable for temperature sensing and luminescence imaging under low and high-power excitation, respectively. • Zn2+, S2−, Mo4+ and V5+ single doped BTO:Er3+/Yb3+ were synthesized by solid state sintering. • The bandgap width of BTO:Er3+/Yb3+ can be tuned by Zn2+, S2−, Mo4+ or V5+ doped. • Zn2+ single doped BTO:Er3+/Yb3+ reaches the maximum UCL intensity under 56.91 W/cm2. • Mo4+ single doped BTO:Er3+/Yb3+ reaches the maximum UCL intensity under 90.95 W/cm2. • The maximum relative temperature sensitivity is 0.00854 K−1 at 303 K. [ABSTRACT FROM AUTHOR]

Er3+-doped germanate-tellurite glasses were prepared by high-temperature melting method, in which structure, luminescent and, temperature-sensing properties were studied. The Raman spectrum indicates that the maximum phonon energy is low, which is 860 cm−1. The transmission spectrum indicates that the infrared transmissive range of glass is wide, visible, and infrared transmittance is high. Parameters of spectral line intensity Ω λ and radiation parameters were calculated based on Judd-Ofelt theory, which showed that the glass has large values of Ω 2 and Ω 6 , and values of Ω 2 and Ω 6 decrease with increasing concentration of Er3+ ions. Strong up-conversion luminescence was obtained at 808, 980 and 1550 nmLD with wavelengths at 534, 553 and 668 nm, respectively, and strong down-conversion luminescence of 1.53 and 2.7 μm also were obtained. The up-conversion emission intensity under three-wavelength simultaneous excitation is significantly enhanced compared to monochromatic excitation. The emission intensity corresponding to the 2H 11/2 → 4I 15/2 and 4S 3/2 → 4I 15/2 transition of Er3+ ions varied with temperature, and the fluorescence intensity ratio FIR of 556 nm and 524 nm increased with increasing temperature. In the temperature range from 330 to 610 K, the maximum sensitivity of glasses was 15.63 × 10−3 K−1 and 19.74 × 10−3 K−1 at T = 570 K, respectively under 808 and 980 nm LD excitation. • An excellent germanate-tellurite matrix glasses were prepared, which have high transmittance (85 %), wide transmission range, low phonon energy (860 cm−1), and large values of Ω 2 (6.98 × 10−20cm2)and Ω 6 (3.92 × 10−20cm2). • The intensity of green or red emission is enhanced by more than double upon simultaneous three-wavelength excitation in contrast to the case that upon monochromatic laser. • The temperature-sensing characteristics indicate that maximum sensitivity S max is 15.63 × 10−3 K−1 and 15.63 × 10−3 K−1 at T = 570 K, respectively under 808 and 980 nm laser monochrome excitation in germanate-tellurite, and is better than other materials. [ABSTRACT FROM AUTHOR]

A series of Ca 0.5 Gd(WO 4) 2 : Ho3+/Yb3+/Bi3+ phosphors prepared by solid-state reaction method were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), elemental mapping, upconversion (UC) spectroscopy and decay time analysis. Under 980 nm excitation, four up-converted emission bands of Ho3+ were observed in all samples. The concentration quenching effect of the UC emission appears by changing the concentration of Ho3+ in Ca 0.5 Gd(WO 4) 2 : x mol% Ho3+, 40 mol% Yb3+ and Yb3+ in Ca 0.5 Gd(WO 4) 2 : 1 mol% Ho3+, y mol% Yb3+, and the optimal concentration of Ho3+ and Yb3+ were determined to be 1 and 40 mol%, respectively. Compared to Bi3+-absent sample, the upconversion luminescence (UCL) intensities of green emission (540 nm) and red emission (644 nm) in Ca 0.5 Gd(WO 4) 2 : 1 mol% Ho3+, 40 mol% Yb3+ via 15 mol% Bi3+ doping were increased by 2.5 and 3.6 times, respectively. The involved UCL mechanism based on the power dependent UC emission spectra were analyzed in detail. Additionally, the temperature sensing performances based on non-thermally coupled levels (NTCLs) 5F 4 (5S 2) → 5I 8 , and 5F 5 → 5I 8 of Ho3+ ions and thermal quenching properties of the samples were also investigated in the range of 298–573 K. The maximum relative sensitivity (S R) of Ca 0.5 Gd(WO 4) 2 : 1 mol% Ho3+, 40 mol% Yb3+ and Ca 0.5 Gd(WO 4) 2 : 1 mol% Ho3+, 40 mol% Yb3+, 15mol% Bi3+ reached 0.0094 K-1 and 0.0112 K−1 at 298 K, respectively. The results indicated that doping Bi3+ ions can enhance the UCL intensity and optical temperature sensing of Ca 0.5 Gd(WO 4) 2 : Ho3+/Yb3+. • Ca 0.5 Gd(WO 4) 2 :Ho3+/Yb3+/Bi3+ phosphors were synthesized by solid-phase reaction method. • The introduction of Bi3+ greatly improves the UCL and temperature sensing properties of Ca 0.5 Gd(WO 4) 2 :Ho3+/Yb3+ phosphor. [ABSTRACT FROM AUTHOR]

A series of Ce3+ and Dy3+ doped LiY 9 (SiO 4) 6 O 2 phosphors was prepared by conventional high temperature solid state reaction method. The dominant emission of Dy3+ originates from the 4F 9/2 → 6H 13/2 (yellow emission) electric dipole transition while that of Ce3+ locates in the blue region. The concentration quenching for Dy3+ emission was investigated by luminescence spectra and decay curves, the main mechanism responsible for the energy transfer between Dy3+ ions was determined by the Inokuti-Hirayama model. Energy transfer from Ce3+ to Dy3+ as well as the temperature sensing property was studied in detail. Thanks to the different thermal responses between Ce3+ and Dy3+ in the host, the highest sensing sensitivity was calculated to be 0.43% K−1. The results demonstrate that LiY 9 (SiO 4) 6 O 2 : Ce3+, Dy3+ may be a potential candidate for a luminescent ratiometric thermometer. [ABSTRACT FROM AUTHOR]

In this study, we report the synthesis and some new crystal structures of tetrakis lanthanide β-diketonate complexes throughout the lanthanide series for homonuclear (Pr3+, Nd3+, Sm3+, Eu3+, Tb3+, Dy3+, Er3+ and Yb3+) as well as for heteronuclear (Eu3+-Tb3+ and Tb3+-Sm3+) complexes. The well-known 1,1,1-trifluoro-2,4-pentadione (Htfac) ligand has been used in the synthesis. Here, we show that when employing the same synthesis conditions, we can obtain complexes with different coordination environments of the lanthanide ions. This is strongly linked to the ionic radius of the lanthanide ion. The luminescence properties of the visible emitting complexes (Ln3+ = Eu3+, Tb3+, Sm3+ and Dy3+) were investigated in solution as well as solid state. The near-infrared emitting complexes (Ln3+ = Pr3+, Nd3+, Er3+ and Yb3+) were recorded in the solid state. The heteronuclear complexes ([Eu 1-x Tb x (tfac) 8 ]2-Na 2 + (x: 0.59 (1) and 0.47 (2), Tb 1-y Sm y (tfac) 8 ]2-Na 2 + (y: 0.1 (3) and 0.2 (4)) and homonuclear complex [Dy(tfac) 4)]−Na+ (DyL 4) exhibited temperature-dependent luminescence properties in the physiological range, with complex DyL 4 showing the highest relative sensitivity S r = 3.45% K−1 (280 K). Complex 2 also showed a high S r = 2.70% K−1 (353 K), which makes them promising for application as physiological luminescence thermometers. To the best of our knowledge until now no lanthanide β-diketonate complexes have been reported for use as good luminescence thermometers operating in the physiological range. Tetrakis β-diketonate lanthanide complexes shows temperature-dependent luminescence in physiological temperature range. Image 1 [ABSTRACT FROM AUTHOR]

Temperature detection based on the fluorescence intensity ratio (FIR) has been considered to be a promising technique for non-contact temperature measurement. Unfortunately, the FIR-based temperature sensor materials generally show low temperature sensitivity because of the narrow energy gap between the thermally coupled energy levels. In this work, lanthanide-doped Ba 3 Y 4 O 9 (BYO) upconversion luminescent materials were synthesized in order to explore their potential application in optical thermometer. The crystal structure of the present samples was investigated by XRD and further refined by the Rietveld method, which indicate that the dopant ions successfully enter the host lattice by occupying Y3+ sites. Excited by 980 nm, BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ present high-purity green and blue output colors, respectively. Based on the analysis of emission intensity ratio and pump-power dependence, the upconversion emission mechanisms are systematically investigated. Subsequently, the temperature sensing performances of BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ based on FIR technique are evaluated in the temperature range of 298–573 K under 980 nm excitation. Owing to the different temperature-dependent behaviors of different emission bands and larger energy gaps, the present materials display high sensitivity, good repeatability and excellent stability. The maximum absolute sensitivity of BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ reach as high as 79.62 × 10−4 K−1 and 193.51 × 10−4 K−1, respectively. Among them, the highest sensitivity of BYO:Tm3+/Yb3+ is far higher than those of other optical temperature sensors using the thermally coupled levels based on FIR technique. The results indicate that the present materials are promising for application as optical thermometer in non-contact temperature detection, and using FIR of 5F 1 /5G 6 and 5F 2,3 /3K 8 multiplets (Ho3+), and 3F 2,3 /1G 4 (Tm3+) are feasible methods for accurate temperature detection. [ABSTRACT FROM AUTHOR]

Tellurite glasses of TeO 2 BaF 2 −REF 3 (RE = La, Gd, and Y) co-doped with Er3+/Yb3+ were prepared and investigated comparatively for optical fiber temperature sensors. For this purpose, their thermal and optical properties were examined in detail. The J-O theory was adopted to estimate the transition properties based on absorption spectra. The dominant green emissions were observed in both of the downshifting and upconversion luminescence. The optical temperature sensing abilities based on the FIR of Er3+ green emissions were studied under both of the UV (380 nm) and NIR (980 nm) excitations. Results show that these three tellurite glasses, especially for the TBG glass, should be very qualified for the design of optical fiber temperature sensors under different excitation modes. [ABSTRACT FROM AUTHOR]

Energy transfer (ET) and cross-relaxation (CR) processes play significant roles in regulating emitting colors and intensity of upconversion (UC) materials. Calculating the coefficients in ET and CR processes can provide visual descriptions for evaluating the UC luminescence properties. Here, we find that those ET and CR processes are responsible for the color-tunable properties in Gd 2 Ce 2 O 7 : Yb3+, Er3+ phosphors. By solving the rate equation, mathematical expressions are established to calculate the ET and CR coefficients based on the experimental UC spectra and lifetimes. The results are benefit to evaluate the efficiencies of ET and CR processes in quantization in different Yb3+ ion concentrations doped samples. The coefficients of ET process arise from 1.05 to 7.93 × 1017 cm3s−1 while those of CR process increase from 2.69 to 72.01 × 1017 cm3s−1 with increasing the Yb3+ ion concentration, which suggest that the CR and ET processes are efficient in Gd 2 Ce 2 O 7 host. Furthermore, potential temperature sensing properties are also evaluated according to the fluorescence intensity ratio of 2H 11/2 and 4S 3/2 levels and the maximal sensitivity (S) is achieved about 0.00337 K−1 at 503 K. This work provides an insight into the evaluation of those UC processes and reveals the capacity in color-tunable and temperature sensing aspects. [ABSTRACT FROM AUTHOR]

Abstract Er3+/Yb3+ co-doped fluorotellurite glasses were prepared. Intense green and red upconversion (UC) emissions corresponding to the transitions of 2H 11/2 , 4S 3/2 →4I 15/2 and 4F 9/2 →4I 15/2 were observed under 980 nm laser excitation, benefiting from the advantages of low phonon energy and good stability of fluorotellurite glasses. Temperature-dependent UC luminescence was carried on glasses with different doping concentration of Er3+ in the range of 298–568 K. Fluorescence intensity ratios (FIR) and absolute sensitivities (S a) were calculated, and the maximal sensitivity value of 54.09 × 10−4 K−1 was obtained at 531 K in the glass with the lowest Er3+ concentration at 0.1 mol%. This study indicates that Er3+/Yb3+ co-doped fluorotellurite glasses can be promising materials applied to non-touching temperature sensors. [ABSTRACT FROM AUTHOR]

A series of novel orange-red phosphors were synthesized in this study by adding Sm3+ into the double perovskite-structured SrLaNaTeO 6 host lattice using a solid-state reaction technique, and their luminescence properties and thermal stability were studied in detail. X-ray diffraction (XRD) analyses revealed that the obtained SrLa 1-x NaTeO 6 :xSm3+ phosphors are triclinically symmetrical, with a space group of Fm-3m. The optimal Sm3+ doping concentration was determined to be x = 0.05 in the SrLa 1-x NaTeO 6 :xSm3+ phosphor, and excessive dopants will cause concentration quenching due to energy transfer interaction between Sm3+ ions. Under the excitation of near-ultraviolet λ ex = 405 nm, the luminous intensity of SrLa 0·95 NaTeO 6 :0.05Sm3+ phosphor at 573 K remained at 125.8% of its original value at 298 K. And then, the phosphor has excellent quantum yield (49.26%) and negative thermal quenching. Besides, the optimum S A and S R values of SrLa 0·95 NaTeO 6 :0.05Sm3+ phosphor were 0.088% K−1@573 K (S A) and 0.149% K−1@498 K (S R), respectively. The excellent negative thermal quenching and good thermal stability of SrLa 0·95 NaTeO 6 :0.05Sm3+ phosphor indicate that it has a potential for applications as white LEDs and optical temperature sensing. In this research, the effect of temperature on the fluorescence intensity and quantum yield of phosphor SrLa 0·95 NaTeO 6 :0.05 S m3+ has been studied. This phosphor exhibits excellent thermal stability and a strong negative thermal quenching. Meanwhile, SrLa 0·95 NaTeO 6 :0.05 S m3+ phosphor can be used to measure temperature based on negative thermal quenching. [Display omitted] • A series of SrLa 1-x NaTeO 6 :xSm3+ orange-red-emitting phosphor is prepared for the first time. • SrLa 0·95 NaTeO 6 :0.05 S m3+ orange-red-emitting phosphor has remarkable negative thermal quenching. • SrLa 0·95 NaTeO 6 :0.05 S m3+ phosphor demonstrates excellent quantum yield (49.26%) and color purity (98.5%). • The intensity ratios of emission bands of SrLa 0·95 NaTeO 6 :0.05 S m3+ phosphor can be used to measure temperature. [ABSTRACT FROM AUTHOR]

Rare-earth ion (RE3+) doped materials with upconversion luminescence and photochromic (PC) effect have received widespread attention, but thermal quenching (TQ) at high temperature and energy-demanding PC recovery processes limit their practical applications. Herein, lanthanide ion doped (K 0.5 Nb 0.5)NbO 3 (KNN) based translucent ceramics were prepared, in which Tm3+/Yb3+ co-doped one displays optical versatility for potential applications in temperature sensors and anti-counterfeiting. By utilizing the large energy mismatch between Tm3+ and Yb3+, negative thermal quenching (NTQ) feature was achieved with the maximum relative sensitivity of 2.54 %K−1 at 213 K. Furthermore, by constructing appropriate intermediate traps, the ceramic exhibits a rapid PC self-recovery process within 30 min without external stimulation. The bifunctional specialty can expand the applications of KNN-based ceramics in optical area. [Display omitted] • Optical bi-functionality in Ln3+ co-doped KNN ceramics were achieved. • Negative thermal quenching (NTQ) was observed in 1 Tm-4Yb-KNN ceramic. • The 1 Tm-4Yb-KNN ceramic exhibits ∼40.3% transmittance in the visible region. • UCPL emission intensity could self-recover in 30 min without external stimulation. • Temperature sensing method was proposed based on both TQ and NTQ ways. [ABSTRACT FROM AUTHOR]

In this paper, we report the photoluminescence (PL) properties of the WO 4 2− group and Dy3+ ions for a new highly sensitive luminescent ratiometric thermometry in Dy3+ doped CaWO 4 (CaWO 4 :Dy) phosphors. Under 259 nm excitation, the violet emission from the WO 4 2− group, as well as the blue and yellow emissions of Dy3+ from the transitions of thermally coupled energy levels (TCLs) of 4I 15/2 and 4F 9/2 , were both investigated, which ascribed to an energy transfer from WO 4 2− to Dy3+. The thermal-enhanced PL of Dy3+ and the thermal-quenched PL of WO 4 2− were detected with increasing temperature. By taking advantage of the opposite temperature-dependent PL evolution, a new thermometry strategy was proposed based on the luminescence intensity ratio (LIR) between Dy3+ and WO 4 2− having a quantitative relationship with temperature. The maximum absolute and relative temperature sensing sensitivities were as high as 449.52*10−4 K−1 and 21.03% K−1 at 300 K, respectively, which were superior to those reported previously for traditional TCLs-based LIR thermometry. This study demonstrated the potential of CaWO 4 :Dy phosphors in temperature sensing and provided guidance for constructing an effective ratiometric thermometry strategy with excellent and reliable sensing performance. • PL emissions from Dy3+ and WO 4 2− were both investigated under 259 nm excitation. • Thermal-quenched PL of WO 4 2− and thermal-enhanced PL of Dy3+ were observed. • Energy transfer from WO 4 2− to Dy3+ led to opposite temperature-dependent PL evolution. • A new ratiometric thermometry strategy was proposed based on LIR of Dy3+ and WO 4 2−. • Ultra-high sensing sensitivities were obtained based on proposed LIR strategy. [ABSTRACT FROM AUTHOR]

At present, improving the sensitivity is one main object for optical temperature sensing. In this work, a series of Yb 3+ -Er 3+ and Yb 3+ -Ho 3+ doped Ca 3 La 6 Si 6 O 24 (CLS) phosphors were designed by solid-state reaction method to develop new rare earth (RE) ions activated upconversion luminescence materials based on thermally coupled and non-thermally coupled levels of Er 3+ /Ho 3+ . For the CLS:0.6Yb 3+ ,xEr 3+ (0.03 ≤ x ≤ 0.18) and CLS:yYb 3+ ,0.03Er 3+ (0.3 ≤ y ≤ 1.2) samples, the relative intensities of Er 3+ different emission peaks change with the RE ions concentrations, which was interpreted by the proposed cross-relaxation (CR) processes. For the CLS:0.6Yb 3+ ,mHo 3+ (0.03 ≤ m ≤ 0.18) and CLS:nYb 3+ ,0.03Ho 3+ (0.3 ≤ n ≤ 1.2) samples, the 5 F 5 - 5 I 8 transition intensity of Ho 3+ shows a continuous decrease with increasing Yb 3+ or Ho 3+ concentrations by normalizing the ( 5 F 4 , 5 S 2 )- 5 I 8 transition of Ho 3+ , which was explained by the CR between Yb 3+ and Ho 3+ . The temperature dependence of the fluorescence intensity ratio for Er 3+ and Ho 3+ emissions was discussed in detail. The relative and absolute sensitivities were compared by using thermally coupled and non-thermally coupled levels of Er 3+ and Ho 3+ . The present investigation could be instructive to develop new luminescent materials with high sensitivity. [ABSTRACT FROM AUTHOR]

Novel YOF:Er,Yb ceramic was successfully fabricated by vacuum hot-press sintering method for the first time, and its phase, microstructure and upconversion luminescence were investigated. It was found that the ceramic showed very dense microstructure with few pores. Under 980 nm excitation, strong green (526 nm and 546 nm) and red (668 nm) upconversion emissions of Er 3+ ions in the ceramic were observed. The upconversion mechanism was proposed based on the power dependence of the upconverted emissions. In addition, the temperature sensing behavior of the YOF:Er,Yb ceramic was investigated from 293 K to 873 K by using the fluorescence intensity ratio technique, and the maximum absolute sensitivity is 0.00882 K −1 at 873 K and the maximum relative sensitivity is 1.35% K −1 at 293 K. These results indicate that the fabricated YOF:Er,Yb ceramic is promising host material for optical temperature sensors. [ABSTRACT FROM AUTHOR]

To validate the reliability of Judd-Ofelt results and the influence of involving absorption transition number, the Judd-Ofelt calculations, in which various transitions were adopted, were carried out for Tm 3+ doped LiYF 4 single crystal. It was found that introducing more transitions into the calculation procedure might get more reliable results. In order to clarify the feasibility of temperature self-reading in Tm 3+ /Yb 3+ doped LiYF 4 single crystal during laser operation, the temperature sensing properties of the single crystal were studied. It was found that the fluorescence intensity ratio of 3 F 2 + 3 F 3 → 3 H 6 to 3 H 4 → 3 H 6 can be used for achieving better temperature detection, and the temperature sensitivity was found much better than that in other materials. [ABSTRACT FROM AUTHOR]

While considering metal oxides co-doped by non-rare earth ions potential for non-contact luminescence thermometry applications, a series of novel Ba 2 LaTaO 6 :Bi3+, Mn4+ phosphors were synthesized and thoroughly tested. Herein we describe the synthesis procedure as well as the results of systematic characterization of the phosphors including phase structure, morphology, luminescence properties and thermal behaviour. The Ba 2 LaTaO 6 :Bi3+, Mn4+ phosphors revealed the presence of dual emission centres with different temperature responses. The maximum absolute and relative sensitivity of the Ba 2 LaTaO 6 :Bi3+, Mn4+ phosphors reached 0.029 K-1 and 3.81% K−1 in the 80–470 K range, respectively. At the same time, the apparent change of Ba 2 LaTaO 6 :Bi3+, Mn4+ emitting colour from blue at 80 K to red at 470 K was achieved, which is readily detected by eye. All the experimental results showed that Ba 2 LaTaO 6 :Bi3+, Mn4+ phosphors have a good potential for application as luminescence temperature sensors. • Novel Ba 2 LaTaO 6 : Bi3+, Mn4+ phosphors were synthesized and tested for application as luminescence optical temperature sensors. • The temperature dependent characteristics of the phosphors are considered using their fluorescence intensity ratios (FIR). • Absolute and relative sensitivities of the phosphors reached 0.029 K-1 and 3.81% K−1 in the range of 80–470 K, respectively • Ba2LaTaO6: Bi3+,Mn4+ emission color varies from blue at 80 K to red at 470 K and can be distinguished with the naked eye [ABSTRACT FROM AUTHOR]

In this paper, the Yb3+-Ho3+ co-doped La 1.55 SiO 4.33 (LSO) phosphors were synthesized by the conventional solid-state reaction method. The phase purity and morphology of the samples were studied by XRD and SEM, respectively. Under 980 nm excitation, the upconversion (UC) luminescence of the LSO:Yb3+,Ho3+ phosphors was checked for different Ho3+ doping content and pump power. The corresponding UC mechanism was interpreted from the changing decay lifetimes and the energy transfer processes between Yb3+ and Ho3+ ions. Meanwhile, the temperature-dependent emission spectra were analyzed to learn the optical temperature-sensing behaviors with the fluorescence intensity ratio (FIR) method. The results revealed that the FIR (I 658 /I 544) value increased when the temperature rose, which followed a linear function. The sensor sensitivity was evaluated, and the LSO:10%Yb3+,2%Ho3+ phosphor showed the highest absolute sensitivity. Besides, the main population way on 5F 5 level of Ho3+ for red emission was clarified by the comparison of the UC spectra excited by continuous-wave and pulse light. Based on the above results, the LSO:Yb3+,Ho3+ phosphor can be considered as a new UC luminescent material for optical temperature sensors. • New Yb3+-Ho3+ co-doped La 1.55 SiO 4.33 phosphors are designed for optical thermometer. • The main population way on 5F 5 level of Ho3+ for red emission was clarified clearly. • High sensitivity is achieved in the La 1.55 SiO 4.33 :Yb3+,Ho3+ samples. • The phosphors are promising as potential candidates in optical thermometer. [ABSTRACT FROM AUTHOR]

In order to develop a new up-conversion luminescent temperature measurement material with a garnet structure, Ca 3 Y 2 Ge 3 O 12 : Er3+, Yb3+ phosphors were prepared by a simple high temperature solid phase method. The structural phase and luminescence characteristics of the samples were characterized by X-ray powder diffraction, field emission scanning electron microscopy and photoluminescence spectra. It can be observed that the characteristic emission of Er3+ ion appears in the sample under 980 nm excitation, and it's up-conversion emission intensity increases with the increase of Yb3+ ion concentration. The maximum relative sensitivity is 1.29 %K−1, 1.09 %K−1 and 1.03 %K−1 based on the different temperature dependence of the thermal coupled energy levels (TCELs), non-thermal coupled energy levels (NTCELs) and the fluorescence lifetime (FL) of 4S 3/2 state, respectively. The results show that Ca 3 Y 2 Ge 3 O 12 : Er3+, Yb3+ phosphor is excellent a material for optical temperature measurement. • Proposed a multi-mode optical thermometer which can measure temperature in three ways: FL, FIR based on TCELs and NTCELs. • Novel garnet structured thermometer Ca 3 Y 2 Ge 3 O 12 : Er3+, Yb3+ shows high relative sensitivity of 1.29 %K−1. • Ca 3 Y 2 Ge 3 O 12 : Er3+, Yb3+ have potential uses for self-referenced optical thermometry. [ABSTRACT FROM AUTHOR]

Rare-earth (RE)-doped ferroelectric materials have received much attention due to their good performance with combined excellent luminescence and electrical properties. In this work, we report multifunctional features with large electrostrain and strong photoluminescence in (Na 0.5 Bi 0.5)TiO 3 -based lead-free piezoelectric ceramics. By introducing RE3+ (RE = Sm, Pr, Eu) ions as activators into the host material with the composition of (Bi 0.5 Na 0.5) 0.94 Ba 0.06 Ti 0.98 (Fe 0.5 Nb 0.5) 0.02 O 3 (BNBT-FN), the ceramics gradually adopts a higher structural symmetry, leading to the destruction of the long-range ferroelectric order, which is conducive to the electrostrain response. When the RE3+ content is 0.6 mol.%, the ceramic samples exhibited large unipolar strains of 0.34–0.39% and high electrostrictive coefficients Q 33 of 0.021–0.029 m4/C2 under an electric field of 80 kV/cm. Furthermore, due to the luminescence activity of the RE3+ ions, the samples exhibited strong red or reddish-orange emission and simultaneously showed good temperature sensing behavior. These results suggest that the RE3+-doped BNT-based materials have great application potential in multifunctional devices. [Display omitted] • Multifunctional features with large electrostrain and strong photoluminescence were obtained. • Good temperature sensing behavior was obtained. • The materials have great potential application in multifunctional devices. [ABSTRACT FROM AUTHOR]

NaGd(WO 4 ) 2 : Er 3+ phosphors by using sodium citrate (Na 3 Cit, Na 3 C 6 H 5 O 7 ) as chelating agent were synthesized via hydrothermal method. The structure and morphology were characterized and analyzed by the X-ray diffraction and field emission scanning electron microscopy. It was found that Na 3 Cit added into the reaction solution considerably influenced the morphologies of samples. The temperature-dependent down-conversion emission spectra of NaGd(WO 4 ) 2 : Er 3+ phosphor under the excitation of 377.5 nm fluorescence with different ratios of Cit 3- /Re 3+ have been measured. The temperature sensing performance for the samples was studied based on the change of emission intensities from two thermally coupled 2 H 11/2 and 4 S 3/2 levels of Er 3+ . It was found that the temperature sensing sensitivities increased with the increase of ratios of Cit 3- /Re 3+ , and the temperature sensing sensitivity can reach a relatively high value of 0.0128 K −1 , which was obtained for the sample with the ratio of Cit 3- /Re 3+ was 1.5. Finally, the physical mechanism of morphology-dependent temperature sensing sensitivity change was explained. [ABSTRACT FROM AUTHOR]

Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ phosphor with respective functions of optical temperature sensing and optical heater are investigated in detail. The Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ film (~200 nm) and powder are successfully prepared, respectively. The crystalline structure is characterized by XRD and the relevant morphologies are analyzed by SEM and AFM, respectively. Based on fluorescence intensity ratio (FIR) technique, photo-thermal behaviors of Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ powder are illustrated. Under 980 nm excitation, the temperature induced by laser is calculated, which varies from 323 to 617 K as exciting power increased from 0.03 to 3.78 W. Additionally, the temperature sensing behaviors of Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ film are investigated. Highly accurate temperature sensing can be realized due to the negligible photo-thermal effect. This thermal sensor exhibited a high sensitivity in the range of 295–660 K, and the maximum value of relative sensitivity was determined as 13.4×10 −3 K −1 at 295 K. These results demonstrate that Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ phosphor can be applied in terms of temperature sensing and optical heater. [ABSTRACT FROM AUTHOR]

In this work, trivalent erbium ion-doped telluro-borate Na 2 Y 2 TeB 2 O 10 (NYTB) phosphor was prepared by a solid-state synthesis. The structure and morphology were comprehensively characterized. The downconversion/upconversion green luminescence of the phosphor was deeply studied. The thermally stable downconversion luminescence at 423 K only loses 10.4% of the intensity at room temperature. The upconversion luminescence has satisfactory temperature sensing properties with the maximum S R parameter of 0.82% K−1. The current research illustrates a new erbium-doped telluro-borate material for lighting and temperature detecting applications. • Na 2 Y 2 TeB 2 O 10 :Er3+ exhibits thermally stable downconversion luminescence. • It exhibits the upconversion temperature sensing properties with high sensitivity. • A Na 2 Y 2 TeB 2 O 10 :Er3+ phosphor with multifunctional applications was developed. [ABSTRACT FROM AUTHOR]

The crystal-field splitting of the 4 f 5 d and 4 f electronic configurations of lanthanide luminescent ions can be modulated by their local coordination environments. In this work, the fluorescence properties of Pr3+:MGd 2 O 4 (M = Sr, Ba) phosphors are successfully modulated based on the site engineering in the M2+ sites. The obtained results indicate that Pr3+ ions would occupy both Sr2+ and Gd3+ sites in Pr3+:SrGd 2 O 4 , while only entering into Gd3+ ones in Pr3+:BaGd 2 O 4. Such an obvious local coordination difference of Pr3+ ions between Pr3+:SrGd 2 O 4 and Pr3+:BaGd 2 O 4 results in an obvious distinction of relevant fluorescence performance. The quenching mechanism of Pr3+ ions in SrGd 2 O 4 conforms to a quadrupole-quadrupole interaction at the lower Pr3+-doped contents and becomes a dipole-dipole interaction with higher Pr3+-doped dosages. In contrast, the quenching mechanism of Pr3+ ions in Pr3+:BaGd 2 O 4 is mainly caused by dipole-dipole interaction. Moreover, combined with the temperature-dependent fluorescence distinctions between the two kinds of Pr3+-doped sites, Pr3+:SrGd 2 O 4 shows an outstanding temperature sensing with a maximum relative sensitivity S r of 2%·K−1 at 150 K. What is discussed in this study demonstrates the potential application of site engineering strategy in adjusting the fluorescence properties of Pr3+ ions and also provides a feasible path for the development of Pr3+-based materials. • The fluorescence properties of Pr3+:MGd 2 O 4 (M = Sr, Ba) are mediated base on site engineering modulation. • The Pr3+ ions occupy both Sr2+ and Gd3+ sites in Pr3+:SrGd 2 O 4 , while only entering into the Gd3+ ones in Pr3+:BaGd 2 O 4. • The concentration quenching mechanism of Pr3+ ion in Pr3+:SrGd 2 O 4 and Pr3+:BaGd 2 O 4 is different. • Pr3+:SrGd 2 O 4 shows an outstanding temperature sensing with a maximum relative sensitivity S r of 2%·K−1 at 150 K. [ABSTRACT FROM AUTHOR]

Realization and optimization of enhanced/tunable optical luminescence properties is highly demanded for reliable and accurate temperature sensing. In this work, uniform monodisperse spherical Er3+/Yb3+ co-doped Y 2 O 3 microcrystals of four different sizes have been synthesized via homogeneous precipitation by changing the reaction time, and the tuning of luminescence intensity/color was achieved by the controllable particles size. On this basis, by studying the particle size dependence of temperature sensing performance, we found that the behavior of absolute sensitivity (S a) and relative sensitivity (S r) have highly size dependence. Interestingly, when different FIR strategies were used (thermally coupled levels (TCLs) and nonthermally coupled levels (non-TCLs)), the sensitivity exhibits the opposite behavior. Importantly, when using the non-TCLs strategy, the maximum S a value for the smallest phosphors was 1.084 K-1, leading to ∼246 times improvement compared to TCLs-based S a. The ultrahigh S a indicated that the Er3+/Yb3+ co-doped Y 2 O 3 phosphors have potential in temperature detection, and the results are of guiding significance to studying the sensitivity of Y 2 O 3 particle size-dependent temperature measurement. • Uniform monodisperse spherical Er3+/Yb3+ co-doped Y 2 O 3 phosphors with four different sizes were synthesized. • A simple, accurate, low cost and large-scale production method was proposed. • Size-dependence of sensitivity by the FIR technique based on TCLs and novel non-TCLs were investigated in detail. • The ultrahigh absolute sensitivity (S a) about 108.4% K−1 under 303 K was obtained. [ABSTRACT FROM AUTHOR]

Er 3+ doped ferroelectric Pb(Mg 1/3 Nb 2/3 )O 3 –0.25PbTiO 3 (PMN–PT) ceramic was grown by using a two-stage sintering method. The sample shows relatively strong upconversion (UC) visible fluorescence under a 980 nm diode laser excitation and the fluorescence spectra were recorded in the temperature ( T ) range of 300–600 K. The fluorescence intensity ratios (FIR) of different energy levels, like 2 H 11/2 , 4 S 3/2 , 4 F 9/2 , and its stark sublevels, were studied as functions of temperature. The responses of FIR adopted here have a linear response to temperature in certain temperature range, and the resolutions achieved for temperature sensing using this material can be 0.5 K with the sensitivity as high as 2.9% K −1 . [ABSTRACT FROM AUTHOR]

The YVO 4 : Er 3+ , Yb 3+ phosphors with various particle sizes were prepared by a precipitation method and the crystal structure and microscopic image were characterized by means of X-ray Diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The up-conversion luminescent spectra of Er 3+ , Yb 3+ co-doped YVO 4 nanocrystals with different particle sizes have been measured. It can be found that the red-green upconversion emission intensity ratio increases with the decrease of the particle size. Furthermore, the temperature sensing properties of YVO 4 : Er 3+ , Yb 3+ phosphors with different particle sizes were studied based on the change of emission intensities from two thermally coupled 2 H 11/2 and 4 S 3/2 levels of Er 3+ . It shows that in a relatively wide range of sensing temperature (293–603 K), the temperature sensing sensitivity of nanosized materials is somewhat higher than that of bulk material. The sensing sensitivity of the sample increases with decreasing particle size, and a relative high sensitivity of 1.112×10 −2 K −1 was obtained for the sample with a particle size of 20 nm, which is about 17.3% higher than the bulk sample. Finally, physical mechanism for the size-dependence of temperature sensing sensitivity was explained and predicted. [ABSTRACT FROM AUTHOR]

In this work, Al 2 W 3 O 12 :1%Cr3+,2%Eu3+ with two discriminable dual emissive centers is synthesized. Both Eu3+ and Cr3+ ions can be excited efficiently by 465 nm. Photoluminescence excitation (PLE) spectra and photoluminescence (PL) lifetime indicate that there is no energy transfer (ET) between Eu3+ and Cr3+ ions. It is worth noting that the photothermal stability of Eu3+ ions is much better than that of Cr3+ ions. Specifically, the ratio of I Cr /I Eu decreases linearly with increasing temperature. Therefore, a blue-LED-excitable luminescent thermometer based on Cr3+/Eu3+ co-doped Al 2 W 3 O 12 is proposed. This developed self-calibrated luminescent temperature sensor possesses the relatively high absolute and relative sensitivity (0.38 K-1 and 2.9% K−1 respectively) as well as good cycle stability among the previously reported TM/Ln-based luminescent; thermometers. These superior features of the developed self-calibrated luminescent thermometer (SCLT) make it a very promising candidate for temperature sensing applications. • A TM/Ln co-doped SCLT Al 2 W 3 O 12 :1%Cr3+,2%Eu3+ is proposed. • Both Cr3+ and Eu3+ ions can be excited by the commercial blue-LED chip. • There is no energy transfer between Cr3+ and Eu3+ in Al 2 W 3 O 12 :1%Cr3+,2%Eu3+. • The SCLT shows high S a (0.38 K-1), S r (2.9% K−1) and cycle stability. [ABSTRACT FROM AUTHOR]

In this paper, the La 2 Mo 2 O 9 :Yb3+, Ho3+, Tm3+ phosphors are successfully synthesized through simple solid-state method. The white up-conversion luminescence is realized by appropriately varying the co-doped concentrations of Ho3+, Tm3+. The up-conversion luminescence characteristics and energy transfer processes of La 2 Mo 2 O 9 :Yb3+, Ho3+, Tm3+ are specifically analyzed upon 980 nm laser excitation. A strategy to enhance the optical temperature sensing performance is demonstrated via flexibly selecting diverse non-thermally coupled energy levels of dual luminescence centers with the fluorescence intensity ratio technology. The maximum values of absolute and relative sensitivity for the thermometer reach 0.2478 K−1 and 1.38% K−1 based on the non-thermally coupled energy levels of 3F 2,3 (Tm3+)/5S 2 ,5F 4 (Ho3+). The luminescence color of La 2 Mo 2 O 9 :Yb3+, Ho3+, Tm3+ phosphors can maintain in the white region over the whole measured temperature range. These results indicate that the phosphors possess great potential in broad application prospects in the aspects of anti-counterfeiting, displays and non-contact temperature sensing. • White luminescence of La 2 Mo 2 O 9 :Yb3+/Ho3+/Tm3+ excited by 980 nm is achieved. • FIR from non-thermally coupled energy levels are used for temperature sensing. • Wide-range and highly-sensitive optical temperature sensing behavior is realized. • The La 2 Mo 2 O 9 :Yb3+/Ho3+/Tm3+ remain white luminescence in wide temperature range. [ABSTRACT FROM AUTHOR]

Here, La 2 MgGeO 6 : Bi3+, Er3+ samples were synthesized by the high-temperature solid-phase method, and the up/down-conversion luminescence properties were investigated with the excitation of near-infrared light (980 nm and 1550 nm) and ultraviolet light (322–378 nm). Under the excitation of ultraviolet light, the sample can exhibit the characteristic broadband blue emission (Bi3+ ions) and green emission (Er3+ ions). When excited with near-infrared light, the sample has only typical green and orange up-conversion emission bands. The green and orange luminescence could be achieved by adjusting the excitation wavelength. In addition, the sample can present multicolor luminescence with the change of pump power and temperature. At the same time, the temperature measurement performance of the phosphor was explored by using the fluorescence intensity ratio technique based on the Er3+ ion thermal coupling energy level (2H 11/2 /4S 3/2) and non-thermal coupling energy level (2H 11/2 /4F 9/2). The maximum temperature sensitivity reached 1.23 %K−1 and 0.99 %K−1, respectively. Therefore, La 2 MgGeO 6 : Bi3+, Er3+ samples could be candidates for multicolor anti-counterfeiting and temperature sensors material. • La 2 MgGeO 6 : Bi3+, Er3+ phosphors are used as a dual-mode temperature sensor to discuss the TCEL and NTCEL. • The phosphor can not only be used in optical temperature measurement, but also can achieve anti-counterfeit encryption. • Polychromatic luminescence can be realized by changing excitation wavelength, temperature and other conditions. • Using FIR technology to explore the temperature sensing performance, the phosphor is highly sensitive to temperature. [ABSTRACT FROM AUTHOR]

Luminescence intensity ratio (LIR) based thermometers provide fast response, excellent accuracy and high spatial resolution. Temperature sensitivity is the most critical parameter for evaluating temperature measurement capability, and it is always interesting to develop novel methods to improve its sensitivity. In this work, we verify that the BaF 2 :Yb/Er NCs with lower phonon energy exhibits better temperature sensitivity than that of CaF 2 :Yb/Er NCs. The maximum relative temperature sensitivity of CaF 2 :Yb/Er NCs was calculated to be 0.596% K−1, while that of BaF 2 :Yb/Er NCs was calculated to be 0.779% K−1. Similar results were also observed through comparing the BaF 2 :Yb/Er@CaF 2 and BaF 2 :Yb/Er@BaF 2 core/shell NCs. Our results provide a novel method that engineering host phonon energy to improve the thermally coupled levels based temperature sensing performance. • Yb/Er co-doped CaF 2 and BaF 2 NCs with similar morphology are prepared. • BaF 2 :Yb/Er based core/shell NCs with different shells are prepared. • The maximum Sr of BaF 2 :Yb/Er is better than CaF 2 :Yb/Er NCs. • The maximum Sr of BaF 2 :Yb/Er@BaF 2 is better than BaF 2 :Yb/Er@CaF 2 NCs. • Decreasing host phonon energy promotes the improvement of temperature sensitivity. [ABSTRACT FROM AUTHOR]

The temperature quenching luminescence effect of optical materials used for fluorescence intensity ratio temperature sensing seriously hinders the realization of temperature sensing in the high temperature region. In recent years, some abnormal thermal enhancement up-conversion materials have attracted extensive attention due to their great potential to sense temperature in high temperature regions. At present, few up-conversion luminescence thermal enhancement materials have reported, and the exploration of thermal enhancement luminescence mechanism is not thorough enough. In this work, new up-conversion luminescence materials Sc 2 W 3 O 12 : Yb3+, Er3+ were prepared, and the thermal enhancement effect was successfully regulated by changing the Yb3+ concentration. The integral emission intensity and intensity of 521 nm at 753 K of Sc 1.42 W 3 O 12 : 0.54Yb3+, 0.04Er3+ can reach 74.5 and 104.9 times of that at room temperature, respectively. In addition, the thermal enhancement luminescence property of up-conversion materials Sc 2 W 3 O 12 : Yb3+, Er3+ was confirmed to be derived from negative thermal expansion properties based on two reference experiments. Finally, the dual temperature sensing model was established to sense the temperature. The results show that the up-conversion thermal enhancement luminescence material is a potential temperature sensing material with high sensitivity, wide temperature sensing range, high resolution and good thermal fatigue resistance. • The thermal enhancement luminescence effect of up-conversion materials can be successfully regulated. • The highest peak emission intensity of Sc 1.42 W 3 O 12 : 0.54 Yb3+, 0.04Er3+ at 753 K can exceed 100 times of that at 303 K. • The thermal enhancement emission of Sc 2 W 3 O 12 : Yb3+, Er3+ was confirmed to be caused by negative thermal expansion. • Temperature sensing materials Sc 1.42 W 3 O 12 : 0.54 Yb3+, 0.04Er3+ show excellent performances. [ABSTRACT FROM AUTHOR]

SrLu 2 O 4 : Yb3+, Er3+ samples were achieved successfully via a traditional solid-state method at 1450 °C. As 980-nm laser exciting, the UC spectra include red and green emissions mainly centering on 665 and 552 nm, respectively. The red is dominant, and the green part is a relative weakness. For all co-doped samples, intense red radiation is obtained. Meanwhile, the experimental formulas about pumping power and spectrum intensity helped us comprehend the up-conversion processes further, and the conclusion is a two-photon process in UC. The 4S 3/2 and 2H 11/2 levels ions are thermal coupled energy levels. We also investigated thermometric characteristics of the samples on the fluorescence intensity ration technology. For SrLu 2 O 4 : Er3+/Yb3+, it can be used as a temperature sensor by using its green emission and red emission, and the sensor sensitivity was calculated. The maximum absolute sensitivity and the relative sensitivity is 0.00226 K-1 and 0.0119 K−1 at 513 K for green emission and the maximum absolute sensitivity and the relative sensitivity is 0.00126 K-1 and 0.0026 K−1 at 303 K for red emission. The fluorescence intensity ratio (FIR) values are almost stable and accurate in repeated tests. As a result, the SrLu 2 O 4 : Er3+/Yb3+ samples would useful hopefully to optical engineering and sensors. • Thedual optical non-contact thermometerSrLu 2 O 4 : Er3+/Yb3+ based on FIR was investigated firstly. • The maximal S A and S R is 0.00226 K-1 and 0.0119 K−1 at 513 K for green emission, • 0.00126 K-1 and 0.0026 K−1 at 303K for red emission. • The fluorescence intensity ratio (FIR) values are almost stable and accurate in repeated tests. [ABSTRACT FROM AUTHOR]

Zn 0.9 Mn 0.1 Al 2 O 4 :Cr3+ phosphors with pure spinel structure were fabricated by using co-precipitation method. The influence of reducing time on the structure, photoluminescence and temperature sensing properties were investigated by using X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and photoluminescence (PL). With the reducing time increasing, the diffraction peak reveals a shift toward lower angle, and the isolated six refined peaks of EPR assigned to Mn2+ in spinel lattices reveal a large increasing overlap, indicating the increasing concentration of Mn2+. A red emission assigned to 2E g →4A 2g of Cr3+ is observed, but its intensity is very tiny in the as-synthesized Zn 0.9 Mn 0.1 Al 2 O 4 phosphors, and with reducing time increasing, the emission intensity is enhanced sharply. The energy level of 2E g is split into 2E(2 A ‾) and 2E(E ‾) corresponding to 687 nm (R 1) and 689 nm (R 2) emissions due to the high crystal field in ZnAl 2 O 4 lattices. The emission assigned to Mn2+-Vo (Oxygen vacancy) at 530 nm reveals a strong temperature dependence, and the highest relative sensitivity of 2.55 %K−1 is achieved based on the luminescence integral intensity ratio of I 530nm / Mn 2+, which is higher than that based on the lifetime of 512 nm emission peak assigned to Mn2+ and based on the luminescence integral intensity ratio of the excitation peaks of I 427nm /I 530nm, indicating that the potential application in multi-reading temperature nanoprobe. [Display omitted] • The samples have good crystallinity and luminescence properties after sintered at 1000 °C. • The luminescence properties of ZnMnAlO:Cr3+ were improved by changing the reduction time. • The change of grain size affects the sensitivity of samples with different reduction time. • The relatively higher sensitivity for optical thermometry is obtained. [ABSTRACT FROM AUTHOR]

Ultra-broadband Vis-NIR (visible to near-infrared) tunable emitting phosphors are considered to the most promising fluorescent materials, such as for the applications in general lighting, NIR spectroscopy, plant growth lighting, and etc. Herein, Ce3+-Cr3+ co-doped Mg 3 Y 2 Ge 3 O 12 phosphors were prepared. Ultra-broadband Vis-NIR luminescence of Ce3+/Cr3+ ranging from ∼500 nm to >900 nm can be observed, which can be tuned with changes of doping concentration or experimental temperature. The energy transfer processes of Ce3+-Cr3+ are investigated by applying the excited state dynamics principle. Interestingly, broadband high-sensitivity temperature sensing performance is obtained for the Ce3+-Cr3+ co-doped Mg 3 Y 2 Ge 3 O 12 phosphors at high temperatures, achieving visible to near-infrared temperature regulation. A single phase phosphor-converted light emitting diode (pc-LED) was fabricated by combining blue LED chip with Mg 3 Y 2 Ge 3 O 12 :Ce3+,Cr3+ phosphors. The interesting results indicate that the prepared phosphors may realize multifunctional advanced applications. • We obtained ultra-broadband Vis-NIR luminescence of Ce3+/Cr3+ ranging from ∼500 nm to >900 nm. • A broadband high-sensitivity temperature sensing performance with S r from 1.38% K−1 to 0.85% K−1 is obtained. • A full-spectrum pc-LED fabricated by only using Mg 3 Y 2 Ge 3 O 12 :Ce3+,Cr3+ can generate white light and broadband NIR light. [ABSTRACT FROM AUTHOR]