Study of multimodal light emissions from Pr3+/Yb3+ doped NaLa(MoO4)2 phosphors for optoelectronic devices and plant-growth applications

Recent advancements in materials design have driven the scientific community to explore phosphor materials for multifunctional applications. This study presents the multimodal light emission (downshifting - DS, quantum cutting - QC, and upconversion - UC) from Pr3+/Yb3+ activated NaLa(MoO4)2 phosphors for multifunctional applications. Under blue (449 nm) and NIR (980 nm) excitation, co-doped phosphors emit visible light through DS and UC processes caused by different f-f transitions of Pr3+ ions. Additionally, when the co-doped samples are excited with blue light, they emit a near-infrared (NIR) light band ranging from 900 to 1050 nm. This is caused by the f-f transition of Yb3+ resulting from energy transfer from a single Pr3+ ion to a pair of Yb3+ ions through the QC process. Concurrently, in-depth investigations were conducted to understand the concentration and thermal quenching mechanism. Firstly, the applicability of phosphors in optical thermometry using the luminescence intensity ratio (LIR) technique was explored, with the maximum relative sensitivity of 0.41% K-1 (448 K). A phosphor-coated LED (pc-LED) was constructed by coupling NaLa0.97Pr0.03(MoO4)2 with a blue LED chip (InGaN). Furthermore, based on the observed optical properties of the prepared phosphor, its application in improving the photovoltaic performance of solar cells and indoor plant applications is systematically discussed.

Upconversion luminescence and thermosensitive properties of NaGd(PO3)4:Yb3+/Er3

High-sensitivity optical temperature measurement has attracted extensive attention in both fundamental studies and practical applications. In this study, a series of upconversion (UC) luminescence phosphors composed of NaGd(PO3)4 (NGP) doped with 20 at% Yb3+ and various concentrations of Er3+ (0.5 at% as the optimal concentration) was synthesized by high-temperature solid-state method. And their crystal structure and the distribution of lanthanide dopants were analyzed using X-ray diffraction with Rietveld refinement verifies. Under 980 nm laser excitation, the obtained phosphors show the characteristic Er3+ upconversion green and red emission bands through two-photon processes. The fluorescence intensity ratio (FIR) based on the thermal coupled states demonstrates the thermal sensing ability in a wide temperature range of 200-573 K. The thermal sensitivity is relatively high with the maximum absolute thermal sensitivity S a of 0.53 % K-1 (523 K) and the maximum relative thermal sensitivity S r of 2.60 % K-1. The phosphor NGP:Yb/Er also exhibits high repeatability as the thermal sensors reach 97 %. These findings postulate the potential of NGP:Yb/Er as a promising candidate in optical thermal sensing applications.

Enhancing thermometric efficiency: a wavelength excitation analysis in LiSrGdW3O12:Tb3+ for superior single band ratiometric (SBR) thermometry

This study delves into the Single Band Ratiometric (SBR) method for luminescence thermometry, specifically employing Tb3+-doped LiSrGdW3O12 (LSGW) as a novel phosphor. The prepared samples crystallize with the tetragonal scheelite structure, with the optimal Tb3+ concentration pinpointed at 0.3Tb3+ ions. When stimulated at diverse wavelengths exhibit luminescence characterized by varying heat dependencies. By utilizing two Fluorescence Intensity Ratio (FIR) parameters for the 544 nm green emission, firstly excited at 405 nm and 488 nm, and then at 405 nm and 379 nm, the Sr relative thermal sensitivity of the luminescent thermometer peaks at 3.56% K-1 and 4.21% K-1, respectively, within the temperature range of 290-440 K. The temperature resolution (δT) of the luminescent thermometer is calculated to be δT1 = 0.68 K and δT2 = 0.75 K for T = 290 K, respectively. These outcomes underscore the applicability of Tb3+ ions for SBR thermometry, emphasizing the impact of the excitation wavelength on the thermal sensitivity. The study lays the groundwork for developing highly sensitive temperature probes by elucidating the interplay of material properties and physical processes.

Er3+-activated Ba2V2O7 upconversion nanosheets for dual-mode temperature sensing

So far, there has been substantial research on non-contact luminescence thermometry approaches that rely on luminescence intensity ratio (LIR) technology. However, there is limited availability of phosphors doped with Er3+ ions that exhibit on-par luminescence and high sensitivity. In this work, samples of Ba2V2O7:Er3+ were synthesized using a sol-gel method aided by citric acid. The luminescence properties of these samples, including upconversion and down-shifting, were investigated using both ultraviolet and 980 nm laser stimulation. When subjected to ultraviolet (UV) light, the sample exhibits a distinct broadband emission that appears pale green. This emission is a distinguishing property of the sample and is attributed to the presence of V2O72- ions. Upon being stimulated by a 980 nm laser, the sample exhibits standard green up-conversion Er3+ emission bands. Concurrently, an assessment was conducted on the phosphor's ability to measure temperature by analysing the LIR between the thermally coupled 2H11/2, 4S3/2 energy levels (TCELs) and the non-thermally coupled 2H11/2, 4F9/2 energy levels (NTCELs) of the Er3+ ion. The corresponding highest sensitivity of temperature for TCELs and NTCELs can position Ba2V2O7:Er3+ nanosheets as a capable option for materials utilized in temperature-sensing applications.

Impact of crystal structure on optical properties and temperature sensing behavior of NaYF4:Yb3+/Er3+ nanoparticles

We report a comprehensive study of the structural, morphological, and optical properties, and UC-based ratiometric temperature sensing behavior of (α) cubic and (β) hexagonal phases of NaYF₄:Yb³⁺/Er³⁺ nanoparticles. The α-NaYF₄:Yb³⁺/Er³⁺ and β-NaYF₄:Yb³⁺/Er³⁺ nanoparticles were synthesized using co-precipitation and hydrothermal methods, respectively. Powder X-ray diffraction studies confirmed the phase purity of the samples. The morphological studies show uniform particle sizes of both phases; the average particle size of α-NaYF₄:Yb³⁺/Er³⁺ and β-NaYF₄:Yb³⁺/Er³⁺ was 9.2 nm and 29 nm, respectively. The Raman spectra reveal five sharp peaks at 253 cm^-1, 307 cm^-1, 359 cm^-1, 485 cm^-1, and 628 cm^-1 for β-NaYF₄:Yb³⁺/Er³⁺, whereas α-NaYF₄:Yb³⁺/Er³⁺ shows two broad peaks centred at 272 cm^-1 and 721 cm^-1. The optical property measurements show that α- and β-NaYF₄:Yb³⁺/Er³⁺ phases have distinct upconversion emission and temperature sensing behavior. The upconversion emission measurements show that β-NaYF₄:Yb³⁺/Er³⁺ has higher overall emission intensities and green/red emission intensity ratio. The temperature-dependent upconversion emission measurements show that α-NaYF₄:Yb³⁺/Er³⁺ has higher energy separation between ²H_11/2 and ⁴S_3/2 energy states. The temperature sensing performed utilizing these thermally coupled energy levels shows a maximum sensitivity of 0.0069 K^-1 at 543 K and 0.016 K^-1 at 422 K for β-NaYF₄:Yb³⁺/Er³⁺ and α-NaYF₄:Yb³⁺/Er³⁺, respectively.

Multi-stimuli-responsive and dynamic color tunable security ink for multilevel anticounterfeiting

Luminescent security features have been used for anticounterfeiting for a long time. However, constant effort is required to strengthen these security features to be ahead of counterfeiters. Here, we developed a multi-stimuli-responsive luminescent security ink containing Tb(ASA)₃Phen, K₂SiF₆:Mn^4+,and NaYF₄:Yb³⁺/Er³⁺luminescent materials in PVC gold medium. Tb(ASA)₃Phen complex shows a broad excitation band in the UV region; upon UV light radiation it shows strong greenish emission of Tb³⁺ions through the antenna effect. K₂SiF₆:Mn⁴⁺, on the other hand, has three excitation bands with maxima at 248, 354, and 454 nm which emit red light after excitation through these bands. NaYF₄:Yb³⁺/Er³⁺is used as an upconverting nanophosphor showing green emission under 976 nm laser excitation. Thus, the multi-stimuli-responsive luminescent security ink shows greenish, red, and green emissions under 367 nm, 450 nm, and 976 nm excitations, respectively. Furthermore, the distinct lifetimes of the activators in Tb(ASA)₃Phen and K₂SiF₆:Mn⁴⁺, i.e. 0.1708 ms and 8.165 ms, respectively, under 380 nm excitation make this ink suitable for dynamic anticounterfeiting as well. The ink shows a change in the emission color with time delay, after the removal of the 380 nm excitation source, from greenish yellow (at 0 delays) to reddish color after a delay of 7.5 ms. These unique optical features along with excellent photo-, chemical- and environmental stability make this ink useful for advanced-level anticounterfeiting.

Efficient dual mode emission in Ce3+/Yb3+/Er3+ doped yttrium aluminium gallium garnet for led device and optical thermometry

By utilizing the effective energy transfer from Ce³⁺ to Yb³⁺, Er³⁺ and from Yb³⁺ to Er³⁺ authors have achieved dual mode emission in Y₃Al₄GaO₁₂ activated with Ce³⁺/Yb³⁺/Er³⁺ ions. Surface morphological and elemental compositions of the prepared samples have been examined using field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS) analysis, respectively. The chemical state of the dopant ions is confirmed by the X-ray photoelectron spectroscopy (XPS). On excitation with 438 nm the prepared material has shown broad visible emission band around 511 nm due to the electronic transition of Ce³⁺ ion. In addition to this sample has also shown NIR emission bands centered around 1024 nm and 1480 nm from Yb³⁺ and Er³⁺ ions, respectively. The emission band at 1024 nm could be due to the quantum cutting (QC) process. Furthermore, up-conversion (UC) emission against temperature and laser power variations is studied on 980 nm excitation wavelength. The prepared sample is used to fabricate visible and NIR LED devices by coating of sample on blue LED chip. Along with this demonstration, optical thermometry ability of the material is studied using emission intensity ratio of two emitting levels. Studies suggest that the prepared material could be useful as dual mode emitting phosphor and LED.

Optical fiber temperature sensor based on the upconversion fluorescence intensity ratio of NaYF4:Er3+ excited by a 1525-nm laser

Remote and accurate temperature measurements in severe environments are of great importance. A 1525-nm wavelength located in the C band of optical fiber communication is used as a pumping light source for NaYF₄:Er³⁺ phosphor possessing high upconversion efficiency. The upconversion luminescence characteristics were demonstrated in the temperature range of 160-400 K. Based on the thermal coupling energy level theory, the temperature measurement principle of the fluorescence intensity ratio is analyzed. The energy gap between the ²H_11/2 and ⁴S_3/2 energy levels of the Er³⁺ ions is approximately 787cm^-1, which is appropriate for a temperature sensor. The experimental results indicated that its maximum temperature sensitivity was 0.00335K^-1. The proposed optical fiber temperature sensor indicates good hysteresis and repeatability and has potential applications in resisting electromagnetic interference and remote temperature sensing.

Optical Temperature Sensing of YbNbO4:Er3+ Phosphors Synthesized by Hydrothermal Method

The novel YbNbO4:Er3+ phosphors were firstly synthesized through the hydrothermal method by adding LiOH·H2O as flux in the H2O/EG system. YbNbO4:Er3+ phosphors showed the agglomerated irregular polygons coexisting with some tiny grains. XRD and Raman spectra were measured to understand the phase structure and the crystal growth mechanism of YbNbO4:Er3+ phosphors. The upconversion (UC) emission spectra, the pump power dependency and UC mechanism were studied under 980 nm excitation. Based on the fluorescence intensity ratio technique, YbNbO4:Er3+ exhibited the maximum sensor sensitivity of 0.00712 K−1 at 220 K, providing a promising application in optical low-temperature sensors.

Wide range color tunability and efficient energy transfer of novel NaCaGd(WO4)3:Tb3+,Eu3+ phosphors with excellent thermal stability for pc-WLEDs

The CIE chromaticity diagram of NCGW:0.6Tb3+,yEu3+ (y = 0–0.4) phosphors assigned to 1–8 along with the corresponding digital photograph excited by 254 nm light and the normalized intensity of the NCGW:0.6Tb3+,0.1Eu3+ phosphor at various temperatures.

Hydrothermal synthesis and tunable up-conversion white luminescence properties of KSc(MoO4)2:Ln3+(Ln = Yb, Er, Tm and Ho) crystals

Pure hexagonal phase KSc(MoO₄)₂crystals with a hexagonal block shape were successfully synthesizedviaa one-step hydrothermal method.

Effect of Synthesis Techniques on the Optical Properties of Ho3+/Yb3+ Co-doped YVO4 Phosphor: A Comparative Study

The Ho³⁺/Yb³⁺-codoped YVO₄ phosphors have been synthesized by three different techniques (viz., solution combustion, sol-gel, and solid-state reaction techniques). X-ray diffraction patterns confirm the formation of a pure phase in the samples synthesized by all of the three methods; however, the average crystallite sizes in the three cases are different. The crystallite size increases if they are heated to higher temperature. The particle sizes are measured by scanning electron microscopy, which shows an increase in particle size with increasing the calcination temperature. The vibrational behavior of all of the three synthesized phosphor samples is studied by the Fourier transform infrared (FTIR) technique. The UV-vis absorption measurements give a large number of bands in all of the three samples prepared by three different methods. The upconversion (UC) emissions in all three samples have been monitored using a 980 nm diode laser. It gives an intense red emission in all of the three samples. Upconversion emission intensity is more prominent in the phosphor sample synthesized by the sol-gel technique and heated at 1473 K. The enhancement in UC emission intensity is well understood by the shape and size of the particles and also confirmed by the FTIR and UV-vis measurements. It is interesting to note that whereas UC measurements give red and weak green emissions, downshifting (DS) measurements show intense green, weak red, and broad blue emissions on UV excitation (323 nm). The DS behavior shows the same characteristics of the enhancement in overall emission. Overall, the phosphor sample synthesized by the sol-gel method gives better results in upconversion and downshifting behaviors when heated at 1473 K.

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

There are two key factors to design an efficient green upconversion (UC) emission based optical sensor for temperature. The primary need is to develop a thermally stable and economical material, for a stable sensor, and the second essence is to get an efficient green UC emission, for high sensitivity of the sensor. The proof of this concept is demonstrated on a model system CaAl₂O₄: Er³⁺, co-doped with Yb³⁺ and Zn²⁺. UC emission of Er³⁺ ion is enhanced, primarily, through co-operative energy transfer from Yb³⁺ to Er³⁺ ions. Secondly, we prove that, incorporation of Zn²⁺ ions alters local crystal field environment around Er³⁺ ions which causes an enhancement in green UC emission. The variation in intensity ratio of ²H_11/2 → ⁴I_15/2 (green) and ⁴S_3/2 → ⁴I_15/2 (green) transitions with temperature is studied to report the sensing property. We show that, sensitivity becomes better with an increase in UC efficiency and the best sensitivity is attained for CaAl_(0.793)2Er_0.007Yb_0.05Zn_0.15O₄ sample, ∼0.0154 K^-1 at 308 K. The obtained result is compared with other works and implies its better suitability. Further, the laser induced optical heating is also observed. The laser induced optical heating has been observed experimentally at 400 K above 1 W laser power. This has been further verified by theoretical justification of heating at various pump powers.

Up-conversion luminescence, temperature sensing properties and laser-induced heating effect of Er3+/Yb3+ co-doped YNbO4 phosphors under 1550 nm excitation

YNbO₄ phosphors with various Er³⁺ and Yb³⁺ concentrations were synthesized via a traditional high-temperature solid-state reaction method. Their crystal structure was investigated by means of X-ray diffraction (XRD) and Rietveld refinements, and it was confirmed that the obtained samples exist in monoclinic phase. The Er³⁺ and Yb³⁺ concentration-dependent up-conversion (UC) luminescence was studied under 1550 nm excitation. By inspecting the dependence of UC intensity on the laser working current, it was found that four-photon and three-photon population processes were co-existent for generating the green UC emissions in the samples with higher Yb³⁺ concentrations. In addition, it was observed that the temperature sensing properties of YNbO₄: Er³⁺/Yb³⁺ phosphors were sensitive to both Er³⁺ and Yb³⁺ doping concentrations. Furthermore, based on the obtained temperature response of the UC luminescence phosphors, 1550 nm laser-irradiation-induced thermal effect was studied, and it was discovered that the sample temperature was very sensitive to the doping concentrations of Er³⁺ and Yb³⁺ and the excitation power.

An upconversion luminescence and temperature sensor based on Yb3+/Er3+ co-doped GdSr2AlO5

GdSr₂AlO₅:Yb³⁺/Er³⁺ micro-particles were synthesized by a simple solid state method. The structure, morphology, size and upconversion luminescence features have been characterized. These results indicated that GdSr₂AlO₅ has a contracted tetragonal cell and has irregular block shaped particles with sizes of about 5 μm. During upconversion, green (²H_11/2, ⁴S_3/2 → ⁴I_15/2) (527 nm, 549 nm) and red (⁴F_9/2 → ⁴I_15/2) (665 nm) emissions had been observed, both of which occurred via a two-photon population process. In addition, green UC emission characteristics were studied, and it was found that its temperature ranged from 293 K to 473 K and the sensitivity was 0.0054 K⁻¹ at 473 K. This indicated that GdSr₂AlO₅:Yb³⁺/Er³⁺ micro-particles may have potential application in high temperature environments for safety signs.

GdSr₂AlO₅:Yb³⁺/Er³⁺ micro-particles were synthesized by a simple solid state method.

Investigation of photoluminescence properties, Judd–Ofelt analysis, luminescence nanothermometry and optical heating behaviour of Er3+/Eu3+/Yb3+:NaZnPO4 nanophosphors

The Er³⁺/Eu³⁺/Yb³⁺:NaZnPO₄ nanophosphors can be used as temperature sensors and optical nano-heaters with significant sensor sensitivity.

808 nm-triggered optical thermometry based on up-conversion luminescence of Nd3+/Yb3+/Er3+ doped MIn2O4 (M = Ca, Sr and Ba) phosphors

808 nm driven UCL mechanism and intrinsic structure-dependent optical thermometric performance of MIn₂O₄:Nd³⁺/Yb³⁺/Er³⁺ (M = Ca, Sr, and Ba) are elucidated.

Up-conversion luminescence of rare earth-doped KGd(WO4)2 phosphors for tunable multicolour light generation

A series of novel KGd(WO₄)₂ crystalline powders doped with Yb³⁺/Tm³⁺, Yb³⁺/Er³⁺ and Yb³⁺/Ho³⁺ were synthesized using a modified Pechini method.

Concentration-dependent spectroscopic properties and temperature sensing of YNbO4:Er3+ phosphors

Er³⁺ concentration had significant influences on temperature sensitivity. The sample with a low concentration of Er³⁺ had high temperature sensitivity.

Sensitivity Modulation of Upconverting Thermometry through Engineering Phonon Energy of a Matrix

Investigation of the unclear influential factors to thermal sensing capability is the only way to achieve highly sensitive thermometry, which is greatly needed to meet the growing demand for potential sensing applications. Here, the effect from the phonon energy of a matrix on the sensitivity of upconversion (UC) microthermometers is elaborately discussed using a controllable method. Uniform truncated octahedral YF₃:Er³⁺/Yb³⁺ microcrystals were prepared by a hydrothermal approach, and phase transformation from YF₃ to YOF and Y₂O₃ with nearly unchanged morphology and size was successfully realized by controlling the annealing temperature. The phonon energies of blank matrixes were determined by FT-IR spectra and Raman scattering. Upon 980 nm excitation, phonon energy-dependent UC emitting color was finely tuned from green to yellow for three samples, and the mechanisms were proposed. Thermal sensing behaviors based on the TCLs (²H_11/2/⁴S_3/2) were evaluated, and the sensitivities gradually grew with the increase in the matrix's phonon energy. According to chemical bond theory and first-principle calculations, the most intrinsic factors associated with thermometric ability were qualitatively demonstrated through analyzing the inner relation between the phonon energy and bond covalency. The exciting results provide guiding insights into employing appropriate host materials with desired thermometric ability while offering the possibility of highly accurate measurement of temperature.

Demonstration of Temperature Dependent Energy Migration in Dual-Mode YVO4: Ho3+/Yb3+ Nanocrystals for Low Temperature Thermometry

A dual mode rare-earth based vanadate material (YVO₄: Ho³⁺/Yb³⁺), prepared through ethylene glycol assisted hydrothermal method, demonstrating both downconversion and upconversion, along with systematic investigation of the luminescence spectroscopy within 12–300 K is presented herein. The energy transfer processes have been explored via steady-state and time-resolved spectroscopic measurements and explained in terms of rate equation description and temporal evolution below room temperature. The maximum time for energy migration from host to rare earth (Ho³⁺) increases (0.157 μs to 0.514 μs) with the material’s temperature decreasing from 300 K to 12 K. The mechanism responsible for variation of the transients’ character is discussed through thermalization and non-radiative transitions in the system. More significantly, the temperature of the nanocrystals was determined using not only the thermally equilibrated radiative intra-4f transitions of Ho³⁺ but also the decay time and rise time of vanadate and Ho³⁺ energy levels. Our studies show that the material is highly suitable for temperature sensing below room temperature. The maximum relative sensor sensitivity using the rise time of Ho³⁺ energy level (⁵F₄/⁵S₂) is 1.35% K⁻¹, which is the highest among the known sensitivities for luminescence based thermal probes.

Large electrostrain and high optical temperature sensitivity in BaTiO3-(Na0.5Ho0.5)TiO3 multifunctional ferroelectric ceramics

Ferroelectric (1 -x)BaTiO3-x(Na0.5Ho0.5)TiO3 ceramics with ferroelectric and up-conversion luminescent multifunctions were designed and fabricated by a solid state reaction process. Their structure, ferroelectric, piezoelectric, up-conversion photoluminescence and relative optical temperature sensing properties were investigated systematically. Crystal structure analysis and Rietveld refinements based on the powder X-ray diffraction data show that the ceramics crystallized in the tetragonal perovskite space group P4mm at room temperature. Enhanced electrical properties and strong green up-conversion luminescence with thermally coupled green emission bands centered at 523 and 553 nm were observed. For a typical sample x equals 0.05, a large electrostrain of 0.279% was obtained under a 70 kV cm(-1) electric field that is comparable to that of the PZT4. Meanwhile, the excellent optical temperature sensitivity (0.0063 K(-1) at 480 K) is higher than that of Er-doped BaTiO3 nanocrystal materials. The results suggest that the BaTiO3-(Na0.5Ho0.5)TiO3 material should be an attractive material for piezoelectric actuator and temperature sensing device applications.

Bright dual-mode green emission and temperature sensing properties in Er3+/Yb3+ co-doped MgWO4 phosphor

The Er³⁺/Yb³⁺ co-doped MgWO₄ phosphor exhibited green UC and DC emission at excited by of 980 nm (a) and 379 nm (b) light, respectively.

Up/down-converted green luminescence of Er3+–Yb3+ doped paramagnetic gadolinium molybdate: a highly sensitive thermographic phosphor for multifunctional applications

Optical temperature sensing and nano-heating behavior of Er³⁺–Yb³⁺ doped multifunctional gadolinium molybdate phosphor.

Investigation into optical heating and applicability of the thermal sensor bifunctional properties of Yb3+ sensitized Tm3+ doped Y2O3, YAG and LaAlO3 phosphors

Bifunctional properties of Yb³⁺ sensitized Tm³⁺ doped Y₂O₃, YAG and LaAlO₃ phosphors were investigated according to experimental and theoretical calculations.

Bioapplications and biotechnologies of upconversion nanoparticle-based nanosensors

Upconversion nanoparticles (UCNPs), which can emit ultraviolet/visible (UV/Vis) light under near-infrared (NIR) excitation, are regarded as a new generation of nanoprobes because of their unique optical properties, including a virtually zero auto-fluorescence background for the improved signal-to-noise ratio, narrow emission bandwidths and high resistance to photo-bleaching.

Host matrix impact on Er3+ upconversion emission and its temperature dependence

Impact of phonon frequency and crystal structure of the host lattice on upconversion emission.

Investigation into the temperature sensing behavior of Yb3+ sensitized Er3+ doped Y2O3, YAG and LaAlO3 phosphors

The sensitivities (S) of Y₂O₃ (YAG/LaAlO₃):Yb³⁺/Er³⁺ phosphors increased with increasing average bond covalency and the calculated values were basically in good agreement with our experimental results.

Stimuli responsive upconversion luminescence nanomaterials and films for various applications

This review highlights recent advances in upconversion luminescence materials in response to various stimuli for a broad spectrum of applications.

Temperature sensor based on ladder-level assisted thermal coupling and thermal-enhanced luminescence in NaYF4: Nd³⁺

NaYF4: Nd³⁺ microprisms were synthesized by a hydrothermal method. The bands of near-infrared (NIR) luminescence originating from the 4F3/2, 4F5/2 and 4F7/2 levels of Nd³⁺ ions in NaYF4: Nd³⁺ microcrystals were measured under 574.8 nm excitation at various temperatures from 323 to 673 K. The fluorescence intensity ratios (FIRs) between any two of the three bands change monotonically with temperature and agree with the prediction assuming thermal couplings. A large relative temperature sensitivity of 1.12% K⁻¹ at 500K is reached with the FIR of 4F7/2 to 4F3/2 levels. In addition, anti-Stokes fluorescence from 4F5/2 level (740 nm) and 4F5/2,7/2 levels (740 nm and 803 nm) of Nd³⁺ ions was studied meticulously under 793.8 nm and 864.2 nm excitations, respectively. The intensities were shown to be greatly enhanced as temperature increases, and the 740 nm band from 4F7/2 level at 458 K increases in intensity by 170 fold relative to that at 298 K under the 793.8 nm excitation.

Down-shifting and upconversion photoluminescence in Ho3+/Yb3+ codoped GdNbO4: effect of the Bi3+ ion and the magnetic field

Energy transfer from host to activator ion, down-shifting, upconversion and effect of magnetic field and Bi³⁺ ions on photoluminescence of Ho³⁺ have been investigated.

Role of Li+ion in the luminescence enhancement of lanthanide ions: favorable modifications in host matrices

The effect of alkali ions on the modification of various host matrices and their effects on the luminescence properties of lanthanide ions have been demonstrated in this comprehensive review.