Near-infrared Luminescence Research Articles

Effect of the Elaboration Method on Structural and Optical Properties of Zn1.33Ga1.335Sn0.33O4:0.5%Cr3+ Persistent Luminescent Nanomaterials.

Near-infrared (NIR) persistent luminescence (PersL) materials have demonstrated promising developments for applications in many advanced fields due to their unique optical properties. Both high-temperature solid-state (SS) or hydrothermal (HT) methods can successfully be used to prepare PersL materials. In this work, Zn1.33Ga1.34Sn0.33O4:0.5%Cr3+ (ZGSO:0.5%Cr3+), a newly proposed nanomaterial for bioimaging, was prepared using SS and HT methods. The results show the crystal structure, morphology and optical properties of the samples that were prepared using both methods. Briefly, the crystallite size of the ZGSO:0.5%Cr3+ prepared using the SS method is ~3 µm, and as expected, is larger than materials prepared using the HT method. However, the growth process used in the hydrothermal environment promotes the formation of ZGSO:0.5%Cr3+ with more uniform shapes and smaller sizes (less than 500 nm). Different diameter ranges of nanoparticles were obtained using HT and ball milling (BM) methods (ranging from 25-50 nm) and by using SS and BM methods (25-200 nm) as well. In addition, the SS-prepared microstructure material has stronger PersL than HT-prepared particles before they go through ball milling to create nanomaterials. On the contrary, after BM treatment, ZGSO:0.5%Cr3+ HT and BM NPs present higher PersL and photoluminescence (PL) properties than ZGSO:0.5%Cr3+ SS and BM NPs, even though both kinds of NPs present worse PersL and PL compared to the original particles before BM. To summarize: preparation methods, whether by SS or HT, with additional grinding as a second step, can have a significant impact on the morphological and luminescent features of ZGSO:0.5%Cr3+ PersL materials.

The ultra-wideband near-infrared luminescence properties and applications of K2SrGe8O18:Cr3+ phosphor

The near-infrared (NIR) light sources are fascinating in real-time nondestructive examination applications. Given that chemical bonds in organic substances (such as C–H, O–H and N–H) have extensive absorption and reflection of light in the NIR region, the emission spectrum of the NIR light sources should be as broad as possible. In this work, ultra-wideband K2SrGe8O18 (KSGO):Cr3+ NIR-emitting phosphors with a 650–1200 nm emission span are developed. Structural analysis combined with electron paramagnetic resonance (EPR), photoluminescence (PL) spectra, time-resolved spectrum (TRES) and temperature-dependent PL spectra confirm that the super broadband emission with full width at half-maximum (FWHM) of 214 nm originates from the double Cr3+ luminescence centers occupying different [GeO6] octahedra. Li+ ion as charge compensator is introduced to balance the negative charge induced by the un-equivalent replacement of Cr3+ for Ge4+, and the PL intensity and thermal stability are greatly enhanced. The NIR phosphor-converted luminescent diodes (pc-LEDs) prepared by combining optimized KSGO:0.10Cr3+, 0.07Li+ samples with 460 nm LED chips demonstrate their application in night vision. The measured absorption spectra of hemoglobin, water, ethyl alcohol and peanut oil illuminated by the as-prepared KSGO:0.10Cr3+, 0.07Li+ phosphors indicate nondestructive analysis in the areas of food safety.

Hexagonal Boron Nitride Seed Layer-Assisted van der Waals Growth of BaSnO3 Perovskite Films.

We have succeeded in obtaining BaSnO3 perovskite thin films with remarkable near-infrared luminescence by van der Waals growth. The films were grown on quartz glass substrates by pulsed laser deposition using hexagonal boron nitride as the seed layer, and their crystallinity was confirmed by X-ray diffraction and cross-sectional transmission electron microscopy. The near-infrared emission of the grown film exhibited a broad emission peak centered at 920 nm. The transparency of the BaSnO3 film (thickness = 1000 nm)/ hexagonal boron nitride /double-sided optically polished quartz glass substrate was approximately 90% at approximately 500 nm with or without the BaSnO3 film. Films showing remarkable near-infrared emission and high transparency obtained by van der Waals-type growth could be used in practical wavelength conversion devices that improve the efficiency of Si single-crystal solar cells. The hexagonal boron nitride seed layer supporting the van der Waals growth is an effective method for high-quality crystal growth of films. It can be used for perovskite-type oxides with many functionalities.

Mn2+ doped LiBaF3 fluoride perovskite single crystal with broadband infrared luminescence pumped by blue LED

In this study, Mn2+ ions doped lithium barium fluoride single crystals (LiBaF3: Mn2+) with perovskite structure were successfully prepared by a reformative Bridgman technique. A near-infrared (NIR) emitting broadband of the single crystal with a peak wavelength of 767 nm and a full width half maxima (FWHM) of 77 nm is owing to the 4T1g(4G)→6A1g(6S) transition of the Mn2+ ions in strong crystal field. Mn2+ ions replace the lattices of Li+ ions from the results of Rietveld structure refinements of the crystals performed by General Structure Analysis System (GSAS) program. A high internal quantum efficiency (41.4%) can be obtained in the synthesized single crystal upon excitation of 494 nm, and the emission intensity of this single crystal at 473 K remains at 42.9% of that at 298 K. Therefore, the LiBaF3: Mn2+ single crystal is a promising candidate for NIR solid-state light-emitting material due to its effective broadband NIR emission. This work offers a novel route to rational design of efficient broadband NIR luminescence and provides a new insight into Mn2+ luminescence and its applications.

A novel near-infrared thermometry based on thermal quenching and negative thermal quenching materials with high sensitivity and accuracy

Near-infrared (NIR) thermometry are attractive with their preeminent superiority in biological tissue. In this work, the thermometry probe with binary near-infrared (NIR) luminescence is prepared from Sc2Mo3O12:Yb/Er and ZrO2:Yb/Ho powders. At elevated temperature from 310 to 580 K, the emission of Er3+ significantly enhanced in negative thermal expansion (NTE) host and the emission of Ho3+ possess thermal quenching in positive thermal expansion (PTE) host. Thus, the probe offers a unique properties of simultaneous emission enhancement and quenching in different NIR wavelengths. By fluorescence intensity ratio (FIR) technique, the relative thermal sensitivity of the sensor can reach a value of 4.2% K−1 higher than NIR thermometers reported to date, while the best temperature resolution is 0.33 K.

Binuclear Copper(I) Complexes for Near‐Infrared Light‐Emitting Electrochemical Cells

AbstractTwo binuclear heteroleptic CuI complexes, namely Cu−NIR1 and Cu−NIR2, bearing rigid chelating diphosphines and π‐conjugated 2,5‐di(pyridin‐2‐yl)thiazolo[5,4‐d]thiazole as the bis‐bidentate ligand are presented. The proposed dinuclearization strategy yields a large bathochromic shift of the emission when compared to the mononuclear counterparts (M1–M2) and enables shifting luminescence into the near‐infrared (NIR) region in both solution and solid state, showing emission maximum at ca. 750 and 712 nm, respectively. The radiative process is assigned to an excited state with triplet metal‐to‐ligand charge transfer (3MLCT) character as demonstrated by in‐depth photophysical and computational investigation. Noteworthy, X‐ray analysis of the binuclear complexes unravels two interligand π–π‐stacking interactions yielding a doubly locked structure that disfavours flattening of the tetrahedral coordination around the CuI centre in the excited state and maintain enhanced NIR luminescence. No such interaction is present in M1–M2. These findings prompt the successful use of Cu−NIR1 and Cu−NIR2 in NIR light‐emitting electrochemical cells (LECs), which display electroluminescence maximum up to 756 nm and peak external quantum efficiency (EQE) of 0.43 %. Their suitability for the fabrication of white‐emitting LECs is also demonstrated. To the best of our knowledge, these are the first examples of NIR electroluminescent devices based on earth‐abundant CuI emitters.

Binuclear Copper(I) Complexes for Near-Infrared Light-Emitting Electrochemical Cells.

Two binuclear heteroleptic CuI complexes, namely Cu-NIR1 and Cu-NIR2, bearing rigid chelating diphosphines and π-conjugated 2,5-di(pyridin-2-yl)thiazolo[5,4-d]thiazole as the bis-bidentate ligand are presented. The proposed dinuclearization strategy yields a large bathochromic shift of the emission when compared to the mononuclear counterparts (M1-M2) and enables shifting luminescence into the near-infrared (NIR) region in both solution and solid state, showing emission maximum at ca. 750 and 712 nm, respectively. The radiative process is assigned to an excited state with triplet metal-to-ligand charge transfer (3 MLCT) character as demonstrated by in-depth photophysical and computational investigation. Noteworthy, X-ray analysis of the binuclear complexes unravels two interligand π-π-stacking interactions yielding a doubly locked structure that disfavours flattening of the tetrahedral coordination around the CuI centre in the excited state and maintain enhanced NIR luminescence. No such interaction is present in M1-M2. These findings prompt the successful use of Cu-NIR1 and Cu-NIR2 in NIR light-emitting electrochemical cells (LECs), which display electroluminescence maximum up to 756 nm and peak external quantum efficiency (EQE) of 0.43 %. Their suitability for the fabrication of white-emitting LECs is also demonstrated. To the best of our knowledge, these are the first examples of NIR electroluminescent devices based on earth-abundant CuI emitters.

Effective ratiometric optical thermometry based on inverse temperature dependent dual near infrared emission of Cr3+ doped BaAl4Sb2O12 phosphor

The device of reliable non-contact ratiometric optical thermometry technique gradually became a cutting-edge research pot over decades due to its intriguing features of rapid response, high accuracy and simple operation. In which, Boltzmann-based optical thermometry has attracted widespread attention for its exceptional reliability. Here in, we put forward an effective ratiometric optical thermometry based on the highly sensitive and effective Boltzmann-based 2E→4A2/4T2→4A2 emission ratio of BaAl3.9Sb2O12:0.1Cr3+. The phosphor shows dual near-infrared luminescence lines at 698 nm and 710 nm (2E→4A2) and the luminescence band near 750 nm (4T2→4A2). With the temperature elevating from 170 to 470 K, the emission intensity of luminescence lines undergoes continuous enhancement and possess excellent anti-thermal quenching property (3.5-fold at 470 K, compared to 170 K). In contrast, the emission intensity of luminescence band shows a monotonic decline trend. The luminescence intensity ratio shows a good linear relationship in the Arrhenius diagram, and the relative sensitivity reaches 2.08 % K−1 at 170 K, which corroborates the BaAl3.9Sb2O12:0.1Cr3+ has the potential as the optical cryogenic thermometer. In the end, the work provides some insights into the development of novel Cr3+-doped thermometry materials based on the 2E and 4T2 energy level transitions in intermediate crystal field environments.

Luminescence Thermometry Based on the Upconversion Luminescence from the Stark Sublevels of BaY2F8:Yb3+, Tm3+ Phosphor.

Visible and near-infrared (NIR) upconversion luminescence (UCL) emissions originating from the BaY2F8: Yb3+, Tm3+ systems were investigated under a laser excitation at 980nm. The BaY2F8:20mol% Yb3+, x mol% Tm3+ and BaY2F8: y mol% Yb3+, 0.5mol% Tm3+ phosphors showed prominent UCL at 800 and 810nm. The optimized doping concentrations of Yb3+ and Tm3+ in the BaY2F8 host matrix were evaluated, their spectroscopic properties were determined, and studies on their temperature-dependent behaviour were carried out. The temperature-sensing properties were studied by generating the fluorescence intensity ratio (FIR) of the UCL peaks originating from the thermally-coupled energy levels of the Tm3+ ions. The Stark sublevels of 1G4 level of Tm3+ ions were utilized to estimate the temperature-sensing abilities of the phosphor.

Optical transition and near-infrared upconversion luminescence properties of YNbO4: Er3+, Yb3+ phosphors

Optical transition and near-infrared upconversion luminescence properties of Er3+ single-doped and Er3+, Yb3+ co-doped YNbO4 phosphors are reported. Based on the framework of Judd-Ofelt theory and modified Judd-Ofelt calculation method, the optical transition properties of Er3+ and Yb3+ ions in YNbO4: Er3+, Yb3+ sample were studied, respectively. The calculated results showed that the absorption cross-section of Er3+ ion at ∼1550 nm is larger than that at ∼980 nm in YNbO4: Er3+ phosphor. And, the absorption cross-section of 2F7/2 → 2F5/2 transition of Yb3+ in YNbO4: 15.0 mol% Er3+, 15.0 mol% Yb3+ sample was calculated to be 138.70 × 10−20 cm2. According to the emission cross section of Er3+ (4I11/2 → 4I15/2) and the absorption cross section of Yb3+ (2F7/2 → 2F5/2), the energy transfer rates from Er3+ to Yb3+ were quantitatively analyzed via the Föster-Dexter model. Furthermore, 1550 nm was selected as the excitation wavelength, the near-infrared upconversion emission spectra of YNbO4: Er3+, Yb3+ samples were measured. It was found that the sample has strong emission at ∼980 nm and the emission intensity was still enhanced with the incorporation of Yb3+.

Structure and spectroscopic properties of Er3+ doped LiNbO3 thin film grown by e-beam evaporation

Er3+ doped LiNbO3 (Er: LN) single crystal films with varied doping levels of Er3+ were grown on z-cut LiTaO3 bulk single crystals by using e-beam evaporation method. The crystallographic orientation, fluorescence properties, ions valence states, Er3+ concentration and Li2O content of films were studied. The main phase of the obtained films is determined to be LN from X-ray diffraction and Raman scattering studies, and the films are found to be orienting along (006). Enhancement in the visible and near-infrared luminescence is observed as the doping concentration of Er3+ is increased. The Li2O content of films is determined using the optical birefringence method and found to be at a constant value of 48.8 mol%, which is consistent with the Raman results. XPS results show that the Er concentration in the films is lower than that in the polycrystalline powder since e-beam evaporation has a low efficiency for heavier Er3+. Fluorescence intensity ratios estimated at different measurement temperatures suggest that the Er: LN films have excellent temperature sensitivity, which shows the potential of the films for optical thermometry applications.

Near-Infrared Photoluminescence of Carbon Nanotubes Powered by Biochemical Reactions of Luciferin/Luciferase.

We report the near-infrared (NIR) photoluminescence of single-wall carbon nanotubes (SWCNTs) generated by chemical energy derived from enzymatic reactions. NIR photoluminescence from SWCNTs has attracted much attention for medical applications, such as bioimaging and biosensors, because of its high transparency and low scattering in biological tissues; however, visible excitation light cannot reach deep tissues. We developed a novel method in which the NIR luminescence of SWCNTs is powered by the biochemical reaction of luciferin/luciferase from fireflies. The luminescence could be detected by a highly sensitive measurement system using an infrared camera, and the optimal conditions for luminescence were investigated. Spectroscopic analysis of the NIR luminescence using chirality-sorted SWCNTs confirmed that the luminescence was derived from SWCNTs. This is the first report achieving NIR photoluminescence of SWCNTs using chemical energy, which does not require external energies, e.g., excitation light or electronic power, and will be applicable to biological imaging and sensing.

Construction of three novel Ln3 compounds using multidentate Schiff base ligand: Crystal structures, fluorescence properties, and biological activities

Three new trinuclear lantharide-based compounds: [Ln3(dbm)5(L)2(CH3OH)]·CH2Cl2 (LnIII = Nd(1), Sm(2), and Tb(3), dbm− = diphthaloylmethae) have been synthesized via the solvothermal method by using a polydentate Schiff base ligand (H2L = (E)-6-(hydroxymethyl)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide) reacting with Ln(dbm)3·2H2O. X-ray diffraction study reveals that all compounds 1–3 belong to monoclinic crystal system with space group C2/c, and compounds 1–3 are isostructural and possess a broken-line Ln3 core. The solid-state luminescence properties measurements indicate that compound 3 displays the characteristic lanthanide luminescence at room temperature. Moreover, photoluminescence properties study show that 1 and 2 display typical NIR luminescence of Nd(III) and Sm(III) ions at room temperature. Furthermore, biological activities research reveals that compounds 1–3 have greater antibacterial activity than the ligand H2L and Ln(dbm)3·2H2O (LnIII = Nd (1), Sm (2), and Tb (3)). The interaction between compounds 1–3 and calf thymus DNA was studied and the results revealed that the compounds were mainly intercalated with calf thymus DNA.

Broadband near infrared luminescent properties of Cr3+ activated SrGa2Si2O8 phosphor

There has been a lot of interest in trivalent chromium ion-doped phosphors for near-infrared (NIR) luminescence in recent years. Here, trivalent chromium-doped NIR emitting SrGa2Si2O8 phosphors were synthesized. The electronic structure was calculated via density functional theory. Although only [SrO7], [SiO4], and [GaO4] polyhedra were found in the host, we still observe broadband luminescence of Cr3+ in the region of 650–950 nm from octahedra site. Due to the doping of Cr3+, a transformation from [GaO4] tetrahedron rearrange into [CrO6] octahedron was produced. The experimental results of X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy demonstrated the presence of Cr3+. A systematic study of the photoluminescence properties of SrGa2Si2O8:Cr3+ was conducted. The luminescent intensity of SrGa2Si2O8:0.005Cr3+ at 420 K can be retained at 83.42% compared to 300 K, indicating its high thermal stability. The electroluminescence of the prepared light emitting diode (LED) based on SrGa2Si2O8:Cr3+ and blue LED chip was measured under various currents. The application as a NIR LED light source was demonstrated in human hands.

Self-Illuminating NIR-II Chemiluminescence Nanosensor for In Vivo Tracking H2 O2 Fluctuation.

Chemiluminescence (CL) imaging, as an excitation-free technique, exhibits a markedly improved signal-to-noise ratio (SNR) owing to the absence of an excitation light source and autofluorescence interference. However, conventional chemiluminescence imaging generally focuses on the visible and first near-infrared (NIR-I) regions, which hinders high-performance biological imaging due to strong tissue scattering and absorption. To address the issue, self-luminescent NIR-II CL nanoprobes with a second near-infrared (NIR-II) luminescence in the presence of hydrogen peroxide arerationally designed. A cascade energy transfer, including chemiluminescence resonance energy transfer (CRET) from the chemiluminescent substrate to NIR-I organic molecules and Förster resonance energy transfer (FRET) from NIR-I organic molecules to NIR-II organic molecules, occurs in the nanoprobes, contributing to NIR-II light with great efficiency and good tissue penetration depth. Based on excellent selectivity, high sensitivity to hydrogen peroxide, and long-lasting luminescence performance, the NIR-II CL nanoprobes areapplied to detect inflammation in mice, showing a 7.4-fold enhancement in SNR compared with that of fluorescence.

Evaluation of the Structural, Near-Infrared Luminescence, and Radioluminescence Properties of Nd3+ Activated TTB-Lead Metatantalate Phosphors

The study reports the structural and spectroscopic properties of Nd3+ doped lead metatantalate phosphor series fabricated by conventional solid state method. XRD results of the PbTa2O6 phase confirm the tungsten bronze symmetry and single-phase structure between 0.5 and 10 mol% Nd3+ concentrations. The lead decrease in the structure can be associated with maintaining the charge balance and single phase due to evaporation during sintering. In SEM micrographs, the grains exhibited shapeless morphology, and the grain sizes varied from 0.5 to 7 m. In EDS results, the increase of Ta/Pb ratio in grain surfaces indicated some lead evaporation, as reported in previous studies. The absorption spectrum of PbTa2O6 host peaked around 275-280 nm, and the band gap was found to be 3.7±0.2 eV. The absorptions of Nd3+ doped phophors shifted the high wavelenght or the low band gap, where the band gaps were found between 3.1±0.2 and 3.3±0.2 eV. The PL emissions of the phosphors in near-inrared region were observed with the transitions of 4F3/2→4I9/2 (at 875 nm) and 4F3/2→4I11/2 (at 1060 nm) of Nd3+. The RL emissions or X-ray excited luminescence were monitored with the transitions of 4F3/2→4I9/2 (at 875 nm), 4F3/2→4I11/2 (at 1065 nm) in the infrared region, and the transitions of 2F(2)5/2→4F9/2, 2F(2)5/2→2H(2)11/2, 2F(2)5/2→4G5/2, 2F(2)5/2→4G7/2, 2F(2)5/2→4G9/2 in the visible region corresponding to at around 430, 455, 490, 525, and 570 nm, respectively. PL and RL emissions of the phosphors exhibited the decreasing emission intensity over 5 mol% due to the concentration quenching which may be associated with cross-relaxing mechanism. In the PL and RL spectral profiles, the similarity of splitting levels was attributed to the similarity of the local symmetry of the ligand ions surrounding the Nd3+ ion. The CIE coordinates obtained using RL emissions were found close to the blue region due to visible region transitions.

Ultra wideband NIR emission in all-inorganic lead-free metal halides through Sb3+ doping

In recent years, food detection, plant photosynthesis, night vision, and the identification of biological data have all benefited from near-infrared luminescence. However, developing metal halides emitting near-infrared (NIR) light is still difficult, which restricts further applicability. Here, we propose an insightful methodology to investigate the wideband NIR emission in metal halide Cs2ZnCl4 host by doping Sb3+. The phosphors are successfully synthesized by the coprecipitation method and the photoluminescent properties are explored in detail. Based on the spectroscopic information, experimental data with DFT calculations, and luminescence kinetics investigation of Sb3+ doped Cs2ZnCl4, the broadband red emission is caused by self-trapped excitons, which can be attributed to the 3P1–1S0 transitions. The spectra under the excitation at 351 nm exhibit an ultra-wideband emission with a center wavelength of 737 nm, an FHWM of 196 nm, and a significant Stokes shift of 386 nm. The NIR LED fabricated by Cs2ZnCl4: Sb3+ can also be used in night vision devices and biological identification. Our findings in Sb3+ doped Cs2ZnCl4 materials provide light on how doping induces emission centers and expand our understanding of the optical characteristics of doped lead-free metal halides for future research. This work also offers recommendations for broadening the range of uses for luminous metal halides and proposes an efficient method for developing fresh environmentally friendly and wideband emission NIR phosphors.

Direct Determination of the Rate of Intersystem Crossing in a Near-IR Luminescent Cr(III) Triazolyl Complex.

A detailed understanding of the dynamics of photoinduced processes occurring in the electronic excited state is essential in informing the rational design of photoactive transition-metal complexes. Here, the rate of intersystem crossing in a Cr(III)-centered spin-flip emitter is directly determined through the use of ultrafast broadband fluorescence upconversion spectroscopy (FLUPS). In this contribution, we combine 1,2,3-triazole-based ligands with a Cr(III) center and report the solution-stable complex [Cr(btmp)2]3+ (btmp = 2,6-bis(4-phenyl-1,2,3-triazol-1-yl-methyl)pyridine) (13+), which displays near-infrared (NIR) luminescence at 760 nm (τ = 13.7 μs, ϕ = 0.1%) in fluid solution. The excited-state properties of 13+ are probed in detail through a combination of ultrafast transient absorption (TA) and femtosecond-to-picosecond FLUPS. Although TA spectroscopy allows us to observe the evolution of phosphorescent excited states within the doublet manifold, more significantly and for the first time for a complex of Cr(III), we utilize FLUPS to capture the short-lived fluorescence from initially populated quartet excited states immediately prior to the intersystem crossing process. The decay of fluorescence from the low-lying 4MC state therefore allows us to assign a value of (823 fs)-1 to the rate of intersystem crossing. Importantly, the sensitivity of FLUPS to only luminescent states allows us to disentangle the rate of intersystem crossing from other closely associated excited-state events, something which has not been possible in the spectroscopic studies previously reported for luminescent Cr(III) systems.

Optical properties of titanate-germanate glasses containing Ho3+ ions

Holmium-doped titanate-germanate glasses have been investigated for optical applications. Near-infrared luminescence at 2 μm due to 5I7 → 5I8 transition of holmium ions has been examined in function of TiO2 concentration. Several spectroscopic parameters for holmium ions such as emission linewidth and lifetime, stimulated emission cross-section and quantum efficiency were determined based on absorption and luminescence experiments and calculated using the Judd-Ofelt theory. Systematic studies demonstrate that holmium-doped titanate-germanate glasses with higher TiO2 concentration show excellent optical properties. Multicomponent glasses with molar ratios GeO2:TiO2 = 1:2 and 1:3 are recommended for near-infrared luminescence at 2 μm.

Infrared to visible up-conversion luminescence of SrF2:Ho particles upon excitation of the 5I7 level of Ho3+ ions

The visible and near-infrared (NIR) up-conversion luminescence (UCL) of a concentration series of fluoride phosphors SrF2:Ho (CHo = 1.3, 3.5, 4.8, 7.4, 8.9, 10.8, 13.0, 13.6 mol.%) upon excitation of the 5I7 level of Ho3+ ions are presented. The dependences of the UCL intensity corresponding to the 5F3→5I8, 5S2(5F4)→5I8, 5F5→5I8, 5I4→5I8, 5F3→5I6, 5I5→5I8, 5F5→5I7, 5I6→5I8 transitions on the concentration of Ho3+ ions were revealed. The UCL energy yield, color coordinates, and correlated color temperature (CCT) values were estimated. The maximum values of UCL energy yields of 0.03% (380–780 nm) and 0.09% (380–1100 nm) were registered for SrF2:Ho (3.5 mol.%) sample. All studied fluoride phosphors are characterized by a red glow of UCL. This glow corresponds to CCT of 6711–7474 K upon incident power density of 28 W/cm2. The UCL mechanisms of SrF2:Ho phosphors were proposed. The SrF2:Ho phosphors can be used as laser beam viewers of the two-micron radiation of thulium and holmium commercial lasers.