Excitation Light Research Articles

Ca2+/Si4+ Modification of the (Gd,Lu)AG Garnet for Enhanced Broadband Cr3+ Luminescence of High Thermal Stability.

Near-infrared (NIR)-emitting phosphors with high quantum efficiency and thermal stability are crucial to NIR pc-LEDs. Garnet-structured (GdLuCa)(Al4-zSiCrz)O12 (z = 0.01-0.2) and (Gd2-xLuCax)(Al4.95-xSixCr0.05)O12 (x = 0.2-1.0) new phosphors with promising NIR luminescence under blue light excitation were designed and fabricated by a solid-state reaction in this work. It was analyzed that the Ca2+, Cr3+, and Si4+ ions would replace Gd3+ in [GdO8], Al1 in [Al1O6], and Al2 in [Al2O4], respectively, and the optimal Cr3+ content is z = 0.05, above which concentration quenching would occur via an electric dipole-dipole interaction. Increasing Ca2+/Si4+ substitution up to x = 1.0 led to luminescence enhancement by a factor of up to 1.85 and internal/external quantum efficiency (%) increment from ∼25.9/10.7 to 63.4/27.5, and all of the phosphors showed excellent thermal stability (I423K/I298K ≥ 87.6%). The luminescence properties of Cr3+ were discussed in detail through systematic investigation of the effects of Cr3+ and Ca2+/Si4+ contents on the crystal structure, local coordination, and crystal field. With the NIR pc-LED device integrated from the optimal phosphor (x = 1.0) and a blue LED chip, electroluminescence manifested potential applications in night vision and medical diagnosis.

Efficient and Ultralong Room Temperature Phosphorescence from Isolated Molecules under Visible Light Excitation.

Visible-light-excited ultralong organic phosphorescence (UOP) materials hold significant potential for various practical applications. Red-shifted excitation wavelength can be achieved by introducing large π-conjugation structures into organic molecules, thereby increasing intermolecular interactions and coupling. However, generating visible-light-excited UOP from isolated molecules poses a great challenge. Herein, we pioneered a strategy to achieve visible-light-excited UOP by doping organic molecules into a rigid polymer. The resulting materials exhibit an ultralong lifetime of up to 2.226 s and a high phosphorescence efficiency of 42.6% under ambient conditions. Impressively, poly(vinyl alcohol) films doped with 1 wt % different guests demonstrate blue and green visible-light-excited UOP. Moreover, they show long-persistent luminescence, lasting over 30 min at room temperature. Through control experiments and theoretical calculations, we discovered that hydrogen bonding between the guests and PVA confines the molecular motion, promoting efficient UOP. The intramolecular charge transfer within the single molecular state contributes to the low energy level, thus leading to the red-shifted absorption. This work will open a new way for developing visible-light-excited UOP based on amorphous polymers, offering highly efficient UOP and long-persistent luminescence under ambient conditions.

Dual–resonance enhancement and polarization control of upconversion luminescence of NaYF4:Yb,Er nanoparticles on 2D metal gratings

In this work, we report enhancement and polarization control of multi–color (green/red) upconversion luminescence (UCL) of lanthanide–doped (NaYF4:Yb,Er) nanoparticles by dual–resonance modes of surface plasmons (SP) on two–dimensional (2D) metal gratings in orthogonal directions. Investigations are performed for the SP resonance modes to be tuned, by adjusting the grating periods, to match any one or two of the green–UCL, red–UCL and excitation wavelengths. It is shown that, for the upconversion nanoparticles (UCNPs) on the 2D gratings with both of the dual resonance modes matching the green–/red–UCL or excitation wavelength, enhancements of the UCLs are roughly doubled, compared with their one–dimensional (1D) counterparts. And when the dual resonance modes match the green– or red–UCL and the excitation wavelength, enhancements of the UCLs are further greatly improved, in spite that the resonance modes for the excitation and emission light are in orthogonal directions. As the emitted UCL photons are largely coupled with the dual SP resonance modes, the radiated green– and red–UCL light can be distinguished by their linear polarization states in orthogonal directions. It is also indicated that polarization of the excitation light can influence the polarization of the UCL light when coupled with the SP resonance modes.

Highly Efficient Spectral Measurement Methods Using Newly Developed High-Throughput Magnetic Circularly Polarized Luminescence System.

Magnetic circularly polarized luminescence (MCPL) spectroscopy is widely used to evaluate the luminescence dissymmetry factor (gMCPL) for compounds. However, even for the same instrument and operating conditions, the measured gMCPL is affected by errors associated with sources such as baseline drift and spectral noise, and so the range of variation of gMCPL must be considered when comparing values, which requires multiple measurements for the same sample. Also, because many samples undergo photodegradation under excitation light, it is difficult to accumulate and average spectra for samples with weak MCPL signals to improve the signal-to-noise ratio. Single measurements must therefore be performed on multiple samples and the results averaged. Furthermore, for samples with a small Stokes shift, spectral correction is required to compensate for the intensity reduction due to the inner-filter effect (IFE). Such measurements are generally performed manually and are therefore time consuming and prone to human error. Here, we demonstrate the use of a newly developed high-throughput MCPL system to automatically measure MCPL and fluorescence spectra of multiple samples of phthalocyanine complexes with high efficiency and reduced human errors. This system allows the incorporation of effective countermeasures to the issues of gMCPL variation, sample photodegradation, extremely weak MCPL signals, and the IFE.

Extending visual range of bacteria with upconversion nanoparticles and constructing NIR-responsive bio-microrobots

The motility of bacteria is crucial for navigating competitive environments and is closely linked to physiological activities essential for their survival, such as biofilm development. Precise regulation of bacterial motility enhances our understanding of these complex processes. While optogenetic tools have been used to control and investigate bacterial motility, the excitation light in most existing systems are limited to the visible light spectrum. Here, we introduce a new type of bio-microrobot comprising genetically engineered E. coli cells and orthogonally emissive upconversion nanoparticles that can respond to both 980 nm and 808 nm NIR light. This system allows toggling of bacterial states between tumbling and swimming via simply alternating the NIR light between different wavelengths. It is believed that the use of NIR light with deeper tissue penetration suggests potential applications for these bio-microrobots in areas like targeted drug delivery.

Unveiling the mechanism for excellent thermal stability in Bi3+-doped Y2O3 phosphors for NUV-pumped WLED applications

In recent years, there has been a growing interest in novel cyan-emitting phosphors to address the cyan gap in the emission spectra of commercial WLEDs. Herein, the cyan-emitting Bi3+-doped Y2O3 (Y2O3:Bi3+) powder was synthesized by a facile solid-state reaction method. XRD analysis confirmed the substitution of Y3+ ions by Bi3+ ions in both C2 and S6 sites within the Y2O3 lattice. The high-purity Y2O3:Bi3+ phosphors under the excitation of NUV light exhibited a prominent cyan emission band centered at 492 nm and a faint violet emission shoulder at 410 nm, attributed to the 3P1 (3A)→1S0 and 3P1 (3Eu) → 1S0 transitions of the Bi3+ ions in the C2 and S6 sites, respectively. The highest PL intensity was achieved with 2%Bi3+ doping and annealing at 1300°C for 5 hours in air. For the first time, it is reported that the PL intensity of Y2O3:Bi3+ phosphor measured at 423 K (150°C) remains at 82% of its intensity at 298 K (25°C), indicating its excellent thermal stability. A mechanism proposing energy transfer from the 3B level of the C2 to 3Eu level of the S6 site in the Y2O3 lattice contributes to the phosphor's thermal stability. It is suggested that the relative PL intensity between 3B and 3Eu levels significantly influences the thermal stability of the Y2O3:Bi3+ phosphors. A cyan LED device was successfully fabricated by coating the Y2O3:Bi3+ phosphor layer onto the top surface of a 310 nm NUV-LED chip. The internal quantum efficiency (IQE) of the Y2O3:2%Bi3+ phosphors was estimated to be approximately 73.85%. These findings indicate that the synthesized Y2O3:Bi3+ phosphor is a promising candidate for use as a cyan-emitting component in NUV-pumped WLED applications.

An effective photocatalytic decomposition of azo dyes by NiO/ZnO/g-C3N4 ternary nanocomposite under solar light excitation

An effective photocatalytic decomposition of azo dyes by NiO/ZnO/g-C3N4 ternary nanocomposite under solar light excitation

Red-emitting phosphors NaLiXF6:Mn4+ (X = Ti, Si) for white LEDs with high color rendering index and low correlated color temperature

White light-emitting diodes (WLEDs) are widely used in various lighting applications due to their high brightness and energy efficiency. However, commercial WLEDs, which typically combine YAG:Ce3+ phosphors with blue light-emitting diode chips, often lack red components, resulting in a high correlated color temperature (CCT) and a low color rendering index (CRI). To address this issue, two novel Mn4+-doped red-emitting phosphors, NaLiTiF6 and NaLiSiF6, were synthesized using an ion exchange method. Both phosphors exhibit strong red light with a pronounced zero-phonon line (ZPL) emission under blue light excitation. Optimal photoluminescence emission intensities were observed at Mn4+ concentrations of 6% for NaLiTiF6 and 9% for NaLiSiF6. When the temperature increased from 303 K to 413 K, both phosphors demonstrated outstanding brightness and chromatic stability. Integrated into phosphor-converted light-emitting diodes (pc-LEDs), the device incorporating NaLiTiF6:6%Mn4+ achieved a CRI of 95.1 and a CCT of 3172 K, while the device with NaLiSiF6:9%Mn4+ showed a CRI of 87.9 and a CCT of 3784 K. In addition, the luminous efficacy, CRI, and CCT of both prototype pc-LEDs maintained minimal variation with increasing driving current. These results indicate the stability and suitability of the synthesized phosphors for enhancing the performance of warm WLEDs applications.

Transforming waste into multifunctional nanomaterials: Mg-doped carbon dots from cow dung for Y(III) detection and biomedical applications

Rare earth metal Yttrium (Y3+) plays a vital role in many electronic devices however, discarding these devices eventually contaminates the environmental sources. Herein, we have developed a Mg-doped carbon dots (M-CDs) as a fluorescent probe for selective and sensitive determination of Y3+ in water bodies. The M-CDs having maximum emission at 420 nm upon 310 nm excitation with 20 % quantum yield and which was synthesized from upcycling of agricultural waste i.e., cow dung by simple carbonization followed by hydrothermal method. M-CDs were confirmed using different analytical and characterization techniques as well as stable in different pH and ionic strength solutions. The M-CDs was highly selective towards Y3+ ions over different metal ions with significant blue shift. This fluorescent probe performs a good linear relationship between the different concentrations of Y3+ ion and fluorescence intensity (R2 = 0.99) within the range of 0.2 to 20 μg/mL with a detection limit of 0.019 µg/mL. The study indicates quenching of Y3+ was result of dynamic quenching and the Inner Filter Effect (IFE) effect. Also, the cytotoxicity of M-CDs was checked via CAM assay and significant growth in blood vascularization with healthy growth of chick embryo confirmed the M-CDs were biocompatible. The nontoxic M-CDs was employed for MCF-7 breast cancer cell imaging which gives bright blue fluoresce under UV light excitation. Further, aiming to a circular economy approach the residual carbon remaining after hydrothermal was used as reactivated carbon for the abatement of environmental pollutants. The sustainable, cost-effective and agricultural waste-derived Mg-doped CDs have potential applications in analytical, environmental, forensic as well as biomedical fields.

Simultaneous bright-field and fluorescence lensless imaging with high excitation light extinction for microfluidics applications

Lensless imaging fluorescence applications are limited by the unavoidable trade-off between the object-sensor distance and the excitation light attenuation at the detection plane. Indeed, a shorter object-sensor distance reduces the spreading of fluorescent signals but at the cost of losing excitation light attenuation provided by filter thickness. Accordingly, the combination of four synergistic pathways to attain further attenuation of excitation light is proposed: the optimization of total internal reflection by microfluidic chip geometry modification, cross-polarization extinction, interchangeable absorption longpass filters, and the CMOS sensor built-in bandpass Bayer filters. The advantages of such a combined setup are demonstrated with a microfluidic application, as we managed to keep the object-sensor distance as short as 600 µm and still distinguish the fluorescence of individual droplets, flowing as close as 650 µm to each other, while attenuating excitation light to an OD 5.9 level. This approach also allowed simultaneous fluorescence and bright-field observation of on-chip droplet fluorescence during flow at a rate of 30 fps. The enhanced capabilities in our scheme pave the way to further lensless fluorescence applications requiring parallelism, lower detection thresholds, and real-time acquisition, such as fluorescence biosensing.

Tailoring of Spectral Behaviors in Ce3+-Activated Ba2Gd8(SiO4)6O2 Cyan-Emitting Phosphors via Site Substitution Engineering for Plant Growth and Full-Spectrum White Light-Emitting Diodes.

Highly efficient Ce3+-activated Ba2Gd8(SiO4)6O2 (BGSO) cyan-emitting phosphors were designed to simultaneously fulfill the applications of plant growth and a white-light-emitting diode (white-LED). Here, the spectral behaviors of the studied samples are manipulated by arranging Ce3+ to occupy various crystallographic sites (i.e., Ba2+ and Gd3+) in BGSO host lattices. Upon ultraviolet light excitation, all the samples emit an intense asymmetric broadband emission from Ce3+ and its fluorescence intensity is strongly impacted by the dopant concentration and occupied position. In addition, the resultant phosphors do not only possess satisfied thermal stability but also present high internal and extra quantum efficiencies of 78.6 and 61.8%, respectively, which can be regulated by selecting the substituted sites. Two cyan-emitting LEDs are fabricated by integrating the synthesized phosphors, and their emission bands align well with the absorption peaks of plant pigments, enabling their uses in plant growth. Furthermore, the controlled plant growth environments also clarify that the packaged cyan-emitting LED can effectively promote plant growth. Additionally, via adopting the resulting phosphors as cyan-emitting converters, full-spectrum white-LED with good electroluminescence behaviors is developed. These findings manifest that the Ce3+-activated BGSO phosphors with tunable spectral properties are promising cyan-emitting components for both artificial plant growth LED and full-spectrum white-LED.

Li+ induced site occupation engineering in Bi3+ activated spinel-type phosphor for multiple optoelectronic applications

The utilization of phosphors for information storage, data encryption, temperature sensing, etc. has been becoming a research hotspot. However, modulating dynamic and pluralistic phosphor emissions is still a huge challenge. Herein, we developed a Li+-induced site occupation engineering in Bi3+ activated Mg2SnO4 (MSO) phosphor with multiple emissions and dynamic afterglow for versatile applications. Experiments and first-principles calculations demonstrated that Bi3+ would simultaneously enter [MgO4] tetrahedron and [SnO6] octahedron to present red and blue emissions, respectively. As Li+ ions were introduced into Mg2SnO4:Bi3+, the preferably generated [LiO4] could hinder the Bi3+ from entering [MgO4] units, so as to force Bi3+ to substitute Sn4+ in [SnO6], thereby leading to strengthened blue emission. Due to the distinct luminescence decay of Bi3+ in tetrahedron and octahedron units, the luminescence colors were regulated from blue to purple and red with enhancing temperature upon UV light excitation, being suitable for luminescence intensity ratio (LIR) thermometer. Moreover, by virtue of the afterglow properties originating from the inherent oxygen vacancies of Mg2SnO4, the dynamic information encryption and anti-counterfeiting by Mg2SnO4:Bi3+, Li+ were achieved. The proposed site occupation engineering can certainly spur several innovative ideas in manufacturing high-performance phosphors for versatile applications.

Cascade of Multiexciton States Generated by Singlet Fission.

Identifying multiexciton states generated from singlet fission is key to understanding the carrier multiplication process, which presents a strategy for improving the efficiency of photovoltaics and bioimaging. Broadband optically detected magnetic resonance (ODMR) is a sensitive technique to detect multiexciton states. Here, we report a dominant species a weakly exchange coupled triplet pair located on adjacent molecules oriented by nearly 90° (V2) under intense light excitation, contrasting to the π-stacked triplet pair under low excitation intensity. The weakly coupled species model precisely reproduces the intricate spin transitions in the Hilbert space of the triplet pair. Combining the magneto-photoluminescence and high-magnetic-field ODMR, we also identify a strongly exchange-coupled state of three triplet excitons formed by photoexcited V2, which manifests through the magnetic-field-induced level crossings between its quintet and triplet manifolds. Our findings demonstrate the microscopic picture of different multiexciton states and the possible transitions among them during exciton fission, which provide insight for the further molecular designs for fission materials.

Ultra-fast photoelectron transfer in bimetallic porphyrin optoelectrode for single neuron modulation

Shrinking the size of photoelectrodes into the nanoscale will enable the precise modulation of cellular and subcellular behaviors of a single neuron and neural circuits. However, compared to photovoltaic devices, the reduced size causes the compromised efficiencies. Here, we present a highly efficient nanoelectrode based on bimetallic zinc and gold porphyrin (ZnAuPN). Upon light excitation, we observe ultrafast energy transfer (~66 ps) and charge transfer (~0.5 ps) through the porphyrin ring, enabling 97% efficiency in separating and transferring photoinduced charges to single Au-atom centers. Leveraging these isolated Au atoms as stimulating electrode arrays, we achieve significant photocurrent injection in single neurons, triggering action potential with millisecond light pulses. Notably, Extracranial near-infrared light irradiation of the motor cortex induces neuronal firing and enhances mouse movement. These results show the potential of nanoscale optoelectrodes for high spatiotemporal modulation of neuronal networks without the need for gene transfection in optogenetics.

Copper-Iodide Hybrid Clusters with Partial Distortion Enable High-Performance Full-Visible-Spectrum White-Light-Emitting Diodes.

Phosphor-converted white-light-emitting diodes (pc-WLEDs) have become increasingly prevalent artificial light sources. Currently, multicomponent phosphors are commonly used for pc-WLEDs, but they often suffer from issues of undesirable reabsorption and unstable emission colors. The potential alternative for pc-WLEDs is a single-component white phosphor that covers the broad visible spectrum with desirable low thermal quenching and efficient luminescence, which is still scarce. To address this challenge, we design a unique single-component white phosphor based on Cu4I4(4-(tert-butyl)-2-(diphenylphosphaneyl)pyridine)2 (Cu4I4(NP-tBu)2) hybrid clusters, which exhibits ultrabroad dual emission from 400 to 800 nm and a high photoluminescence quantum yield of 97% under 320 nm light excitation. Based on time-resolved fluorescence spectroscopy and theoretical model analysis of our Cu4I4 series clusters, we hypothesize that the dual emission comes from the coexistence of two triplet states caused by partial cluster distortion under light excitation. The Cu4I4(NP-tBu)2 cluster's high structural stability also endows consistent spectral performance and low thermal quenching up to 240 °C. Thus, the fabricated pc-WLED using Cu4I4(NP-tBu)2 white phosphor exhibits a maximum efficiency of 63.4 lm/W and maintains a high color rendering index of ∼88 during 1000 h of continuous operation. Our results highlight a new strategy of low-cost and high-performance copper-iodide cluster-based single-component white phosphors for high-quality pc-WLEDs.

Exploring and Regulating Heteroatom-Electronegativity-Associated with Ring Aromaticity and Excited State Intramolecular Proton Transfer Mechanism for Benzothiazole-Based Fluorophore.

A novel fluorophore 2-(2'-hydroxy-5'-benzaldehyde phenyl) benzothiazole (HBBT) with excited state intramolecular proton transfer (ESIPT) characteristics, showing good selectivity for Cu+/Cu2+ ions had been synthesized experimentally (Molecules 2022, 27, 7678). However, its ESIPT mechanism and fluorescent performance related to atomic substituents have not been investigated systematically. In this work, two HBBT derivatives, 2-(2'-hydroxy-5'-benzaldehyde phenyl)benzoimidazole (HBBI) and 2-(2'-hydroxy-5'-benzaldehyde phenyl)benzopyrrole (HBBP), were obtained by respectively using -NH and -CH2 groups in place of the sulfur atom in the thiazole ring. The absorption/emission spectra and ring aromaticity as well as ESIPT processes of HBBT and its derivatives were studied using density functional theory (DFT) and time-dependent DFT (TD-DFT). The simulated absorption and fluorescence wavelengths of HBBT agreed well with the corresponding values obtained in the experiment. According to the analyses of geometry structures, electron densities, and infrared vibration frequencies, the intramolecular hydrogen bond becomes stronger upon light excitation. The frontier molecular orbitals were analyzed via establishing potential energy curves, and the ESIPT behavior was described deeply. Obviously, the NH-substitution makes ring 4 more aromatic, while the CH2-substitution changes ring 4 from aromatic to antiaromatic. The ESIPT process helps to alleviate the excited state antiaromaticity. The greater the antiaromaticity of the S1 state normal form, the higher the barrier of ESIPT.

Development of a Photoelectrochemical Microelectrode Using an Organic Probe for Monitoring Hydrogen Sulfide in Living Brains.

Hydrogen sulfide (H2S) is an important bioactive molecule that plays a significant role in various functions, particularly in the living brain, where it is closely linked to cognition, memory, and several neurological diseases. Consequently, developing effective detection methods for H2S is essential for studying brain functions and the underlying mechanisms of these diseases. This study aims to construct a novel photoelectrochemical (PEC) microelectrode Ti/TiO2@HSP for the quantitative monitoring of H2S levels in the living brain. The PEC microelectrode Ti/TiO2@HSP is formed by covalently bonding a specifically designed organic PEC probe HSP, which possesses a D-π-A structure, to the surface of TiO2 nanotubes generated via in situ anodic oxidation of titanium wire. The PEC probe HSP can effectively react with H2S and generate significant photocurrent response under long-wavelength excitation light (560 nm), thereby achieving quantitative detection of H2S. The sensor demonstrates high sensitivity and good selectivity. In vivo experiments utilizing the PEC microelectrode Ti/TiO2@HSP enable the monitoring of dynamic changes in H2S levels across various regions of the mouse brain. The findings reveal that in normal mice, the concentration of H2S in the hippocampus is significantly higher than in the striatum and cerebral cortex. Additionally, following propargylglycine drug stimulation, H2S concentrations in different brain regions were observed to decrease, with the most substantial reduction noted in the hippocampus. This suggests that cystathionine γ-lyase (CSE) is the primary enzyme responsible for H2S production in this area, while the striatum exhibits a less pronounced decrease in H2S concentration, indicating a reliance on alternative enzymatic pathways for H2S production. Therefore, this study not only successfully develops a high-performance H2S detection sensor but also provides new experimental tools and theoretical foundations for further exploring the roles of H2S in neurophysiological and pathological processes.

High-power, frequency-doubled all-polarization-maintaining fiber laser system at 925 nm.

We demonstrate a high-power 925-nm pulsed laser system based on a frequency-doubled, all-polarization-maintaining (PM) fiber laser source operating at 1.8 µm. The seed is a figure-9 mode-locked oscillator, which incorporates a nonlinear amplifying loop mirror. After power scaling and pulse compression, the 1.8-µm laser source can provide femtosecond pulses with a repetition rate of 31.3 MHz and an output power of 2.24 W. Through frequency doubling in a nonlinear crystal, the 925-nm laser delivers a pulse duration of 503 fs and an output power of 818 mW, which is the highest power provided by all-PM fiber laser systems at this wavelength, as far as we know. Furthermore, this 925-nm all-PM fiber laser is employed as the excitation light source for two-photon microscopy (TPM) and second-harmonic generation (SHG) microscopy.

Optimization of band structure by facet engineering to enhance photocatalytic/photothermal synergistic therapy of cobalt sulfide nanosheets

With the rapid development of optics and nanotechnology, optical therapy is recognized as a potential strategy to combat bacterial drug resistance. Unfortunately, the limitation of band structure on the therapeutic effect of photocatalytic nano-antimicrobial materials has become a major challenge in the development of optical therapy. Here, Co9S8 and Co9S8-T200 were prepared by facet engineering design with major exposed facets (311) and (222), respectively. The experimental results demonstrate that the antimicrobial ability of Co9S8-T200 was significantly higher than that of Co9S8 under the excitation of near-infrared light. Theoretical calculations show that the (222) facets can modulate the d-band center of Co9S8-T200 closer to the Fermi energy level. This promotes the binding of the intermediate to the active site. The strong adsorption capacity for O2 and H2O and the high efficiency of electron-hole pair separation facilitate the production of reactive oxygen species dominated by singlet oxygen, and the photocatalytic therapy is effectively enhanced. In addition, Co9S8-T200 has a narrow bandgap to promote photothermal conversion efficiency and light absorption capacity and exhibits excellent photothermal therapy. This work expands new ideas for the development of superior optical antimicrobial agents with synergistic photothermal and photocatalytic therapy.

Combined dual-channel fluorescence depth sensing of indocyanine green and protoporphyrin IX kinetics in subcutaneous murine tumors.

Fluorescence sensing within tissue is an effective tool for tissue characterization; however, the modality and geometry of the image acquisition can alter the observed signal. We introduce a novel optical fiber-based system capable of measuring two fluorescent contrast agents through 2cm of tissue with simple passive electronic switching between the excitation light, simultaneously acquiring fluorescence and excitation data. The goal was to quantify indocyanine green (ICG) and protoporphyrin IX (PpIX) within tissue, and the sampling method was compared with wide-field surface imaging to contrast the value of deep sensing versus surface imaging. This was achieved by choosing filters for specific wavelengths that were mutually exclusive between ICG and PpIX and coupling these filters to two separate detectors, which allows for direct swapping of the excitation and emission channels by switching the on-time of each excitation laser between 780- and 633-nm wavelengths. This system was compared with two non-contact surface imaging systems for both ICG and PpIX, which revealed that the fluorescence depth sensing system was superior in its ability to resolve kinetics differences in deeper tissues that would normally be dominated by strong signals from skin and other surface tissues. Specifically, the system was tested using pancreatic adenocarcinoma tumors injected into murine models, which were imaged at several time points throughout tumor growth to its diameter. This demonstrated the system's capability to track longitudinal changes in ICG and PpIX kinetics that result from tumor growth and development, with larger tumors showing sluggish uptake and clearance of ICG, which was not observable with surface imaging. Similarly, PpIX was quantified, which showed slower kinetics over different time points, and was further compared with the wide-filed imager. These results were further validated through depth measurements in tissue phantoms and model-based interpretation. This fluorescence depth sensing system can be used to sample the interior blood flow characteristics by ICG sensing of tissue as deep as 20mm into the tissue with sensitivity to kinetics that are superior to surface imaging and may be combined with other imaging modalities such as ultrasound to provide guided deep fluorescence measurements.