Excited State Absorption Process Research Articles

Localized surface plasmon resonance induced nonlinear absorption and optical limiting activity of gold decorated graphene/MoS2 hybrid

The synergistic supremacy of a hybrid nanocomposite made of reduced graphene oxide (rGO), molybdenum disulfide (MoS2) and gold nanoparticles (Au) for Q-switching and optical limiting applications is investigated. Hydrothermally synthesized Au-rGO-MoS2 hybrid with varying concentrations of Au (2.5, 5, 7.5 and 10 wt%) was subjected to interact with Q-switched Nd:YAG nanosecond green laser pulses. The intensity dependent nonlinear absorption studies revealed a switch over in the nonlinear behaviour from saturable absorption (SA) to reverse saturable absorption (RSA) behaviour. SA occurs due to ground state bleaching at comparatively lower laser irradiances serving the need for Q-switching and optical communications. The RSA trait at higher laser irradiance is attributed to sequential two-photon absorption which serves as the platform for optical limiting behaviour prompting laser safety and effective photothermal therapy applications. The strong mid-visible and UV absorption promotes the availability of multiple energy bands for energy transitions of excited state absorption (ESA). Enhanced local fields due to localized surface plasmon resonance effect, structural defects, hierarchical morphology, increased absorption cross-section and plasmon induced energy transfer promotes robust ESA process. These tunable nonlinear optical properties make Au-rGO-MoS2 hybrid promising futuristic candidates for applications in nonlinear photonic devices, ultrafast optical switches and all-optical signal processing systems.

Dual-wavelength mid-infrared laser operation at 2.8 μm and 3.6 μm in Er3+ doped fluoride fiber

This study presents a pioneering experimental demonstration of dual-wavelength laser operation at 2.8 μm and 3.6 μm in an Er3+-doped ZrF4-BaF2-YF3-AlF3 double-cladding fluoride glass fiber, fabricated in-house. The achievement is realized through the implementation of a novel dual-wavelength pumping scheme utilizing 980 nm and 1150 nm lasers. This innovative scheme enables the excitation of the lower energy level of the 2.8 μm laser transition (4I11/2) to the upper energy level of the 3.6 μm transition (4F9/2) via an excited state absorption process, resulting in simultaneous emission at 2.8 μm and 3.6 μm. The maximum laser output powers at 2.8 μm and 3.6 μm are measured at 0.96 W and 0.32 W, respectively. This groundbreaking work marks the first experimental realization of dual-wavelength laser operation at 2.8 + 3.6 μm in Er3+-doped fluoride fiber, contributing significantly to the advancement of laser technology in this spectral range.

Role of host matrix on NIR emission and ratiometric thermometry properties in Nd3+/Yb3+ co-doped CaGd2(MO4)4 (M = W, Mo) phosphors

The development of ultrasensitive thermometric phosphors has become an active area of research due to their appealing applications in the contactless temperature detection field. Herein, the scheelite-related compounds—CaGd2(WO4)4: Nd3+, Yb3+ and CaGd2(MoO4)4: Nd3+, Yb3+, which exhibit high sensing capacity—are successfully prepared and systematically characterized. The X-ray diffraction analysis reveals that CaGd2(WO4)4: Nd3+, Yb3+ exhibits the monoclinic structure, whereas CaGd2(MoO4)4: Nd3+, Yb3+ is in the tetragonal phase. The maximum phonon cut-off energy of CaGd2(WO4)4: Nd3+, Yb3+ is 929 cm−1, slightly larger than that of CaGd2(MoO4)4: Nd3+, Yb3+ (904 cm−1). Irradiated by 980 nm laser, PL spectra consist of the Nd3+: 4Fj → 4I9/2 (j = 7/2, 5/2, 3/2) and Yb3+: 2F5/2 → 2F7/2 emissions located in the near-infrared (NIR) range. Negative and positive thermal quenching behaviors are observed for the emissions of Nd3+ (754, 802, and 868 nm) and Yb3+ (1008 nm), respectively, attributed to the cooperative effects of the phonon-assisted energy transfer process of Yb3+ → Nd3+ and excited state absorption process of Nd3+. Moreover, the host material can affect the luminescence properties, thermal enhancement factor of the NIR anti-Stokes emission, and thermal sensing performance of the Nd3+-Yb3+ pair. Consequently, CaGd2(MoO4)4: Nd3+, Yb3+ exhibits higher sensing sensitivity (Sr-max = ∼6.00%K−1) than CaGd2(WO4)4: Nd3+, Yb3+ (Sr-max = ∼5.56%K−1). This study provides useful information for the construction of high-performance ratiometric thermometers based on the inverse thermal dependence of the NIR emissions of Nd3+ and Yb3+ ions.

Two-photon absorption induced optical limiting action of Ag-doped lanthanum molybdate decorated reduced graphene oxide nanocomposites

In this research, we aimed to investigate the linear and non-linear optical properties of Ag-La2(MoO4)3@RGO nanocomposites. For this purpose, Graphene Oxide (GO) was synthesized by Modified Hummer’s method after which GO was chemically reduced to Reduced graphene oxide (RGO). The nanocomposite Ag-doped La2(MoO4)3 is prepared by a simple and facile co-precipitation method. The prepared nanocomposite was characterized by Fourier transform infrared (FTIR), Ultraviolet-Visible (UV-Vis) absorption, X-ray diffraction (XRD), Scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX). XRD and EDX analysis indicated the reduction of GO and successful synthesis of Ag-doped La2(MoO4)3 nanocomposite. FESEM images portray the presence of thin layers of graphene sheets and Ag-doped La2(MoO4)3 on the sheets of reduced graphene oxide. Ground state absorption studies show that the reduction of graphene oxide causes a hypsochromic shift in the absorption maxima of the graphene layers. The photoluminescence of Ag- La2(MoO4)3@RGO demonstrates the utmost emission in the UV range caused by the valence band and conduction band's direct transitions in the band gap region. Z-scan method using Nd: YAG laser exposes that both nanocomposite and specific counterparts hold reverse saturable absorption behaviour. The source of optical limiting action is attributed to the excited state absorption process, emerging from the influence of the plasmon resonance state of Ag nanoparticles. Strong nonlinear absorption and lower onset limiting threshold make the Ag-La2(MoO4)3@RGO nanocomposite desirable material for laser safety devices.

Single-shot pump-probe technique by the combination of an echelon and a grating with a time window of 109 ps

In this study, using only a single pulse, pump-probe measurement with a large time window of more than 100 ps is implemented. A commercial grating is used to encode a time window of ∼56 ps in a single pulse; therefore, there is no need for machining customization. In addition, in this technique, the grating surface is accurately imaged, eliminating the image blur problem caused by phase differences in previous echelon-based techniques. Moreover, to make full use of the grating surface and obtain a larger time window, a simple reflection echelon is combined that matches the grating in the time window. This combination encoding strategy results in a total time window of ∼109 ps and maintains accurate imaging of the grating surface. This time window is an order of magnitude greater than the maximum reported values of the echelon encoding strategy and the angle beam encoding strategy. To demonstrate this single-shot pump-probe technique, the two-photon absorption process of ZnSe and the excited-state absorption process of a symmetrical phenoxazinium bromine salt were studied. The possibility of further improving the experimental setup is also discussed.

Upconversion photoluminescence and optical temperature probe of Er3+/Yb3+ co-doped LAZT glass prepared by containerless aerodynamic levitation method

xEr3+/yYb3+ co-doped La2O3-Al2O3-ZrO2-TiO2 ([30-(30/88) × (x + y)]La2O3-[58-(58/88) × (x + y)]Al2O3-4ZrO2-8TiO2: x mol% Er2O3/y mol% Yb2O3, x = 2 mol%, and y = 4, 8, 12, 16, 20 mol%, abbreviated as: LAZT: xEr/yYb) glasses were synthesized using a containerless aerodynamic levitation technique. The maximum phonon energy, fluorescence performance and optical temperature measurement performance of the prepared glasses were studied. Raman test shows that the maximum phonon energy of all glasses is less than 355 cm−1, in which the low phonon energy can provide an excellent internal environment for the induction of fluorescence effects. Under excitation at 980 nm, all samples exhibit noticeable red emission peak centering at 662 nm and feeble green emission peak centering at 549 nm at room temperature. The luminous intensity reaches the highest value at x = 2 mol% and y = 12 mol%, at which the concentration quenching phenomenon occurs. The fluorescence mechanism of LAZT: xEr/yYb involves a double-photon process, in which the energy transfer process (ET) accounts for the main part and the excited state absorption process (ESA) accounts for the secondary part. The fluorescence intensity ratio (FIR) can be used for temperature sensing, and the absolute sensitivity FIR reaches maximum value of 1.3 × 10−2 K−1 at 79 K. These results indicate that the LAZT: 2Er/12Yb glass is expected to become a candidate material for non-contact optical temperature probe.

Difference of carrier dynamics in a semiconductor saturable absorber mirror with and without B+ ion-implantation.

Three samples whose growth temperatures were 450°C, 500°C, and 560°C for S E S A M 1, S E S A M 2, and S E S A M 3, respectively, were tested by femto-second time-resolved transient absorption spectroscopy. The results indicate that the carrier dynamics of excited state absorption were dominant, and the lifetimes of carriers trapped by defect levels were about tens of pico-seconds. To further study the influence of carrier dynamics and recovery time of samples by ion-implantation, B + ions of 80 and 130 KeV were implanted into the samples with dose of 1014/c m 2. The modified samples showed a dominance of ultra-fast carrier dynamics of ground-state bleaching and direct recombination, which lasted for hundreds of femto-seconds, over excited state absorption. Additionally, carrier fast trapping was observed to be competitive with the excited state absorption process. After ion-implantation, the carrier dynamics of carrier trapping were enhanced, which contributed to forming an ultra-short laser, while the carrier dynamics of absorption of the excited state were suppressed. The conclusion that defect levels were partially eliminated by B + ion-implantation can be drawn.

A novel ultrahigh-sensitive optical thermometer based on inverse thermal responses of Nd3+ and Yb3+ emissions in BaGd2(MoO4)4 phosphor

Nowadays, lots of efforts have been vested on the exploitation of novel luminescent thermometric materials to achieve remote temperature readout with ultra-high sensitivity and sub-degree resolution. Herein, the BaGd2(MoO4)4: Yb3+, Nd3+ phosphors were successfully prepared via a solid-state reaction method, and their concentration/temperature-dependent luminescence behaviors were investigated systematically. Upon 980 nm excitation, the photoluminescence (PL) spectra consisted of three emission bands centered at 754 nm, 805 nm and 872 nm from Nd3+, together with an emission band peaked at 1008 nm from Yb3+. As the temperature elevated, the Yb3+: 2F5/2 → 2F7/2 emission weakened sharply, whereas the promoted phonon-assisted energy transfer process from Yb3+ to Nd3+ and excited-state absorption process of Nd3+ led to an intense thermal enhancement of the Nd3+: 4Fj → 4I9/2 (j = 7/2, 5/2, 3/2) transitions. Moreover, the thermally enhancing factor was found to depend on the Nd3+ concentration. By utilizing the luminescence intensity ratio (LIR) technique, the temperature sensing behaviors based on thermally coupled levels (Nd3+: 4Fj, j = 7/2, 5/2, 3/2) and non-thermally coupled levels (Nd3+: 4Fj and Yb3+: 2F5/2) were studied at the different doping concentrations. When the temperature sensing was based on LIR between Nd3+: 4F3/2 → 2I9/2 and Yb3+: 2F5/2 → 2F7/2 transitions, the BaGd2(MoO4)4: 3 mol%Nd3+, 15 mol%Yb3+ sample displayed excellent thermal sensitivity (2.28–8.42 %K−1) and temperature resolution (0.1–0.22 K) at temperatures ranging from 298 K to 573 K, which were superior to those of many other reported luminescence materials. The present work might give a new input for developing near-infrared (NIR) luminescence materials with desirable temperature sensing performances.

Adjusting the nonlinear optical and optical limiting properties of MAPbBr3/PMMA by doping with Zn

Third-order nonlinear optical and optical limiting properties of MAPbBr3/polymethyl methacrylate (PMMA) are adjusted by doping with Zn. X-ray diffraction and photoluminescence are performed to confirm the effective doping of Zn. Typical reverse saturable absorption and self-focusing effects are observed in the undoped MAPbBr3/PMMA and Zn-doped MAPbBr3/PMMA. After Zn doping, the nonlinear absorption coefficient becomes larger but nonlinear refraction coefficient becomes smaller. This may be related to the decreased defect states after Zn doping. Besides, both values of the optical limiting threshold and the clamping normalized transmittance for the Zn-doped MAPbBr3/PMMA are obviously smaller than those of the undoped sample, indicating that its optical limiting property enhances. The reverse saturable absorption properties are caused by one photon absorption-induced excited-state absorption processes, which have been explained by using three-energy-level diagrams. The nonlinear optical and optical limiting properties of the Zn-doped MAPbBr3/PMMA make it show great potentials for application in optical limiter.

Excited-state absorption in light-scattering Er:CaSc2O4 ceramic

Excited-state absorption (ESA) in visible from the I13/24 level in the upconversion phosphor Er:CaSc2O4 is investigated. ESA spectra are recorded in the spectral range 400 - 750 nm in ceramic optically-scattering Er(2 at.%):CaSc2O4. The ESA spectra are calibrated to cross-section units and separated from other processes (luminescence, stimulated emission) taking place in this spectral range. ESA from the I11/24 level is also noticed and discussed. The cross-sections of the various ESA processes in the visible spectral range are found. The precision of the calibration method is discussed.

2.7 μm mid-infrared Er-doped thin-film LiNbO3-on-insulator photonic wire laser

The 2.7 μm continuous-wave laser was demonstrated theoretically on the basis of a 1480-nm-pumped Er-doped thin-film LiNbO3-on-insulator photonic wire (Er:LNOI PW) and a three-level rate equation model of Er3+. Under 1480 nm pumping, the excited state absorption (4I13/2 → 4I9/2) and cooperative upconversion process (4I13/2 → 4I15/2: 4I13/2 → 4I9/2) populate the 4I11/2 level meanwhile bypass significantly the 4I13/2 level, enabling a population inversion between these two levels. The cavity length and output coupler's reflectivity at laser wavelength were optimized for maximizing laser output. Under the optimum configuration, dependences of laser power on both pump power and Er3+ concentration were investigated. Simulation results show that lower threshold pump power, higher laser output and slope efficiency are obtained for a higher Er3+ concentration. The laser output reveals a linear relationship to the Er3+ concentration and the relationship is strong at higher pump level. Simulation results show that the threshold pump power, laser output and slope efficiency are on orders of several tens of mW, sub-mW and 3.1%, respectively, for an Er3+ concentration of 1.5 mol%. In addition, there is no need to account for photorefractive effect on the laser performance as it is far smaller than the refractive index contrast of the LNOI PW, ∼0.7. Present work opens up the possibility of implementing an on-chip 2.7 μm mid-infrared laser based on an Er:LNOI.

Nature of Linear Spectral Properties and Fast Relaxations in the Excited States and Two-Photon Absorption Efficiency of 3-Thiazolyl and 3-Phenyltiazolyl Coumarin Derivatives.

Coumarin-based fluorescent agents play an important role in the manifold fundamental scientific and technological areas and need to be carefully studied. In this research, linear photophysics, photochemistry, fast vibronic relaxations, and two-photon absorption (2PA) of the coumarin derivatives, methyl 4-[2-(7-methoxy-2-oxo-chromen-3-yl)thiazol-4-yl]butanoate (1) and methyl 4-[4-[2-(7-methoxy-2-oxo-chromen-3-yl)thiazol-4-yl]phenoxy]butanoate (2), were comprehensively analyzed using stationary and time-resolved spectroscopic techniques, along with quantum-chemical calculations. The steady-state one-photon absorption, fluorescence emission, and excitation anisotropy spectra, as well as 3D fluorescence maps of 3-hetarylcoumarins 1 and 2 were obtained at room temperature in solvents of different polarities. The nature of relatively large Stokes shifts (∼4000-6000 cm-1), specific solvatochromic behavior, weak electronic π → π* transitions, and adherence to Kasha's rule were revealed. The photochemical stability of 1 and 2 was explored quantitatively, and values of photodecomposition quantum yields, on the order of ∼10-4, were determined. A femtosecond transient absorption pump-probe technique was used for the investigation of fast vibronic relaxation and excited-state absorption processes in 1 and 2, while the possibility of efficient optical gain was shown for 1 in acetonitrile. The degenerate 2PA spectra of 1 and 2 were measured by an open aperture z-scan method, and the maximum 2PA cross-sections of ∼300 GM were obtained. The electronic nature of the hetaryl coumarins was analyzed by quantum-chemical calculations using DFT/TD-DFT level of theory and was found to be in good agreement with experimental data.

Pump Excited-State Absorption at 442 ± 1 nm for Efficient Visible Fluoride Fiber Lasers

In the well-known excited-state absorption (ESA) process, population inversion of the laser transition can be achieved by a strong pump ESA involving a lower laser level. The exploitation of pump ESA has expanded from the visible to the near-infrared spectral range, based on various laser sources. Extending the operating wavelength of the pump ESA is greatly significant for the development of rare-earth-doped fluoride fiber lasers. Herein, we report, presumably, the shortest operating wavelength of pump ESA at 442 ± 1 nm for an efficient continuous-wave visible fluoride fiber laser. A novel scheme for direct blue diode pumping was proposed and demonstrated in an Ho <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped fluoride fiber. Utilizing a 442 ± 1 nm blue laser diode, single-wavelength ground-state absorption (GSA) and ESA pumping mechanism were investigated not only for double populating of the upper laser level by GSA and ESA, but also to depopulate the lower laser level by ESA. We report a slope efficiency of 50.3% with respect to the launched pump power of 442 ± 1 nm and an output power of up to 327 mW for a 750 nm fiber laser. This result is an order of magnitude higher than that previously reported for a directly blue-diode-pumped deep-red Ho <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped fluoride fiber laser. Moreover, the numerical modeling results were in good agreement with the experimental results. Our approach represents a significant advancement for blue pump ESA in visible fluoride fiber lasers, which opens new capabilities for blue-diode pumping for a wide range of future applications.

Synthesis, Photoswitching Behavior and Nonlinear Optical Properties of Substituted Tribenzo[a,d,g]coronene.

A family of tribenzocoronene derivatives bearing various substituents (3) were constructed through the Diels-Alder reaction, followed by the Scholl oxidation, where the molecular structure of 3b was determined via single crystal X-ray diffraction analysis. The effect of substitution on the optical and electrochemical property was systematically investigated, with the assistance of theoretical calculations. Moreover, the thin films of the resulting molecules 3b and 3e complexed with fullerene produced strong photocurrent response upon irradiation of white light. In addition, 3b and 3e exhibit a positive nonlinear optical response resulting from the two-photon absorption and excited state absorption processes.

High performance Pt(II) complex and its hybridized carbon quantum dots: Synthesis and the synergistic enhanced optical limiting property

A new strategy is launched to develop efficient nonlinear optical (NLO) materials by incorporating organometallic Pt(II) complexes into carbon quantum dots (CQDs), which exhibits the synergistic effect for the optical limiting performance of hybrid materials. m1-CDs were further functionalized with Pt(II) complex for the smaller sizes (2.3 nm) and more surface amino groups (54.6 %), and the Pt(II) complex also shows long triplet-excited lifetime (482 ns) and satisfactory reverse saturable absorption (RSA). The hybrid material N-CD-Pt exhibits the special π − π* transitions and broader metal-to-ligand/intraligand/ligand-to-ligand charge transfer transitions in the visible region (∼675 nm). The electron/energy transfer process occurred among the system causes a significant emission quenching for the nanohybrid, which is benefit for the occurrence of excited-state absorption process and the enhancement of the RSA. The covalent modification also endows nanohybrid N-CD-Pt with improved NLO performance, including RSA behaviors mainly from the Pt(II) complexes and nonlinear scattering responses from CQDs. The limiting threshold (F50) of N-CD-Pt reaches 0.62 J·cm−2 at 532 nm, which is better than Pt(II) complex (1.0 J·cm−2).

Fabrication and comprehensive structural and spectroscopic properties of Er:Y2O3 transparent ceramics

Transparent Er:Y2O3 ceramics with sub-micron grain size (<1 μm) were fabricated by using one-step vacuum sintering followed by hot isostatic pressing (HIPing) technique. The transmission of the undoped Y2O3 reaches 83%. The structural characteristics including the phonon energy were investigated through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) analysis and scanning electron microscopy (SEM) measurement. The overall spectroscopic properties of transmission, fluorescence emission up to 3000 nm, lifetime, up-conversion luminescence, and refractive index were systematically studied for both 0.25 at% and 7.0 at% Er:Y2O3 ceramics with different thicknesses. The comparison of the spectra of the fluorescence emission and up-conversion luminescence under both 976 and 808 nm laser excitation was performed. The multiple high-energy-state transitional processes after the excited state absorption (ESA) processes involved in the up-conversion are discriminated between the multi-phonon non-radiative transitions and the radiative transitions according to the measured maximum phonon vibrational energy. The calculation was performed based on the Judd–Ofelt theory.

The role of surface related quenching in the single band ratiometric approach based on excited state absorption processes in Nd3+ doped phosphors

One of the newest approaches to ratiometric luminescence thermometry, namely, the single band ratiometric (SBR) approach, that involves excited state absorption, has been intensively investigated in recent years due to its unique features. The development of the highly sensitive luminescent temperature probe based on this approach is possible only when the physical processes and material parameter of the phosphors that affects the probability of the excited state absorption will be determined. Therefore, in this work, for the first time, the influence of phosphor size and the role of surface quenching processes on the sensitivity of this type of luminescent thermometers are investigated and discussed. It has been shown that surface related depopulation processes of the intermediate 4I11/2 energy levels strongly affect the intensity of the 4F3/2→4IJ emission excited by excited state absorption. It leads to a reduction of the sensitivity of this type of luminescent thermometers and a narrowing of its usable temperature range. As a consequence, it has been shown that the maximum relative sensitivity of YAG:Nd-based thermometer changes as follows 2.38 %/oC, 8.46 %/oC and 9.51 %/oC for a phosphor in the form of nanocrystals, microcrystals and ceramics, respectively.

Spectroscopy and Near-Infrared to Visible Upconversion of Er3+ Ions in Aluminosilicate Glasses Manufactured with Controlled Optical Transmission

In this work we report on the spectroscopic properties and the near-infrared to visible upconversion of Er3+ ions in aluminosilicate glasses manufactured by directionally solidification with the laser floating zone technique. Glasses were manufactured in a controlled oxidizing atmosphere to provide them with high optical transmission in the visible spectral range. Absorption and emission spectra, and lifetimes were assessed in both the visible and the near infrared spectral range. Green upconversion emissions of the 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions at 525 nm and 550 nm attributed to a two-photon process were observed under excitation at 800 nm. Mechanisms responsible for the upconversion luminescence were discussed in terms of excited state absorption and energy transfer upconversion processes. Excitation spectra of the upconverted emission suggest that energy transfer upconversion processes are responsible for the green upconversion luminescence.

Near-infrared dyes for two-photon absorption in the short-wavelength infrared: strategies towards optical power limiting.

This work provides an overview of the recent advances in the field of two-photon absorbing chromophores active in the short-wavelength infrared (SWIR) spectral range. Herein the common strategies and main structure-property relationships that lead to near-infrared (NIR) electronic absorption of chromophores are described. A complete review of the molecules that feature two-photon absorption (2PA) beyond 1100 nm is presented for the purpose of further use in optical power limiting applications in the SWIR band. Recent progress in the development of optical power limiting in this particular spectral region is reported with emphasis on the use of the two-photon induced excited state absorption (ESA) process as an optical power limiting enhancer.

Excited State Absorption for Ratiometric Thermal Imaging.

Luminescence thermometry, an alternative to thermal imaging using the thermovision technique, requires the development of new approaches and a thorough understanding of the physical phenomena involved, in order to improve the temperature readout parameters. A phenomenon that has recently been shown to cause an extremely strong increase in the emission intensity for the temperature elevation is the thermally induced excited state absorption. This work demonstrates that taking advantage of the strong thermal dependence of the thermally induced excited state absorption process, the limitation associated with the two thermally coupled excited levels usually involved in the ratiometric temperature readout can be overcome, improving the thermometric properties of the luminescent thermometer. The same excitation wavelength was used to induce the emission resulting from the thermally induced excited state absorption of the Tb3+ ions and ground-state absorption of the other type of co-dopant ions causing the opposite nature of the thermal dependence of their emission intensities. Moreover, thanks to the strong color changes exhibited by the phosphors, it was possible to demonstrate the applicability of the proposed approach for through-object 2D thermal imaging of a microelectronic printed circuit board covered with a glass plate using an ordinary commercial digital camera, where the thermovision camera fails.