Green Upconversion Emission Research Articles

Upconversion photoluminescence and radiative properties of Ba2CaWO6: Er3+ phosphors for photonic applications

Trivalent erbium doped Ba2CaWO6 phosphors were synthesized by the solid-state reaction method. Nephelauxetic ratio and bonding parameter were calculated from the absorption spectrum in order to understand the nature of Er3+ ion-ligand bonds in the prepared phosphor samples. The phenomenological Judd-Ofelt (JO) analysis has been implemented to the recorded absorption spectrum of Ba2CaWO6: Er3+ phosphors for evaluating the JO parameters. Under 980 nm laser diode excitation, Ba2CaWO6: Er3+ phosphor exhibits strong green (4S3/2 →4I15/2) and weak red (4F9/2 →4I15/2) upconversion (UC) emissions centered at 566 and 680 nm and an intense downconversion NIR emission at 1.5 μm. The UC process were assessed on the basis of power dependence of upconversion emission intensity. The significant luminescence features observed from the photoluminescence spectra of Ba2CaWO6: Er3+ phosphors that comprise of both up conversion and down conversion luminescence were discussed in detail with the aid of partial energy level diagram. The better values of radiative properties, luminescence features and CIE color coordinates suggest the suitability of Er3+ doped Ba2CaWO6 material for various photonic applications.

Synthesis, Neutron Diffraction, and DFT Studies of NaLa(WO4)2: Yb3+/Er3+; NIR Induced Green Fluorescent Bifunctional Probes for In Vitro Cell Imaging and Solid State Lighting

AbstractWe report the synthesis, systematic crystal structure, and upconversion (UC) emission in bulk and nanomaterials of NaLa(WO4)2: Yb3+/Er3+. The disordered NaLa(WO4)2 matrix has been considered as the UC host and host lattice dynamics were investigated using DFT, and neutron diffraction studies. The presence of phonons at the cut‐off frequency of ∼912 cm−1 is revealed by DFT analysis which is further confirmed by room temperature Raman studies. The optimized concentration of NaLa0.865Er0.035Yb0.1(WO4)2 is referred to as UCB and UCN with respect to particle size derived from a facile solvothermal method. Interestingly, high‐resolution microscopy studies uncovered the existence of high‐density edge dislocations in UCN nanomaterials leading to enhanced phonon scattering. Both UCB and UCN materials have shown pump power‐dependent intense UC green emission upon 980 nm laser irradiation. In addition, we have also demonstrated an excellent non‐toxicity of UCB and UCN towards Escherichia coli, Staphylococcus aureus, Candida albicans, and mammalian HeLa cell lines followed by the potential use of nanomaterials for in vitro cell imaging. Thus, the combined neutron diffraction, DFT, microscopy, and spectroscopic analysis collectively resulted in the right structure‐property relationship in these biocompatible UC green fluorescent bifunctional NaLa(WO4)2 materials.

Ultra-High-Sensitive Temperature Sensing Based on Er3+ and Yb3+ Co-Doped Lead-Free Double Perovskite Microcrystals

Fluorescence intensity ratio (FIR) thermometry, a new contactless temperature measurement, can achieve accurate measurements in a harsh environment. In this work, all-inorganic lead-free Cs2AgInCl6: Er-Yb and Cs2AgBiCl6: Er-Yb microcrystals emit bright green up-conversion emission, which are synthesized by precipitation at a low temperature (80 °C). In up-conversion emission, FIR of the 2H11/2 → 4I15/2 band to the 4S3/2 → 4I15/2 band exhibits temperature dependence, which can be used as the temperature measurement parameter, so-called FIR thermometry. Moreover, the theoretically accurate measurement range is from 100 to 600 K, achieving maximum absolute sensitivities from 0.0130 to 0.0113 K-1, respectively. The principle of up-conversion and high sensitivity is well explained by calculating the partial density of states. Compared to the reported thermometry materials based on the FIR method, the prepared all-inorganic lead-free Cs2AgInCl6: Er-Yb and Cs2AgBiCl6: Er-Yb microcrystals show outstanding temperature measurement width and sensitivity, becoming a potential candidate for high-sensitivity optical temperature sensors.

Effect of fluorine substitution on the structure and spectral property of fluorotellurite glass for upconversion luminescence thermometry

A series of TeO2–ZnO–ZnF2–La2O3–Yb2O3–Er2O3 glasses (TZL) with different amount of ZnF2 were prepared by the melt quenching method. The effects of fluorine concentration on the density, refractive index, thermal behavior, and vibrational characteristic of TZL glasses were analyzed. The Judd-Ofelt (J-O) theory was employed to study the spectroscopic properties of Er3+ ions. By using the J-O intensity parameters the spontaneous radiative transition probabilities, fluorescence branching ratios, and radiative lifetimes of some concerned transitions of Er3+ were predicted. The potential of TZL glasses for the gain around 1.5 μm was briefly evaluated. Moreover, the upconversion luminescence was investigated under the excitation of 980 nm laser. The dependence of luminescence intensity on pump power revealed that the upconversion luminescence of Er3+ in TZL glasses are contributed by two-photon involved energy transfer processes. Furthermore, the adjacent upconversion green emissions of Er3+ ions were used to temperature sensing based on the fluorescence intensity ratio (FIR) technique. High absolute sensitivity and resolution have been obtained, which indicate that the TZL glasses are potential materials for optical fiber temperature sensors.

Upconversion luminescence and non-contact optical temperature sensing in Ho3+-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 lead-free ceramics

A series of Ho3+-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 lead-free piezoelectric ceramics (NBT-0.06BT: xHo3+, 0.0025≤x ≤ 0.03) are prepared by a conventional solid-state reaction method. Under the excitation of 980 nm, all the samples exhibit strong green, red and near infrared upconversion emissions, which are ascribed to the 5F4/5S2→5I8 (∼547 nm), 5F5→5I8 (∼656 nm), 5F4/5S2→5I7 (∼756 nm) transitions of Ho3+ ions, respectively. The NBT-0.06BT: 0.015Ho3+ ceramic displays the optimal emission among these Ho3+-doped NBT-0.06BT solid solutions. Optical thermometry behavior is evaluated via fluorescent intensity ratio (FIR) of green to red emissions of Ho3+ ions. The temperature sensing performances is investigated in the temperature range of 293–473 K based on non-thermally coupled levels (NTCL). The maximum relative sensitivity is found to be 0.35% K−1 at 293 K. The present investigation results imply the promising application of NBT-0.06BT: Ho3+ in non-contact optical thermometers.

High-reliability all-fiber FIR temperature sensor using LiGd(WO4)2:Er3+/Yb3+ phosphors

Rare earth doped LiGd(WO4)2 phosphors have been prepared by solid sintering technology. The dominant 4G5/2→6H9/2 emission of Sm3+ ions suggests that Sm3+ ions occupy the non-centrosymmetric lattices in LGWO:Sm3+ phosphors. Under the excitation at 980 nm laser, bright green upconversion emissions at 531 nm and 553 nm were detected in LGWO:Er3+/Yb3+ phosphor, which was used to build a high-reliability temperature sensor based on fluorescence intensity ratio (FIR) technology. The calibration curve between FIR and temperature was established at the temperature range of 258–423 K. The highest absolute sensitivity was 0.0137 K−1 at 423 K and the standard deviation of multiple temperature measurements at 313 K was only 0.108%. Experimental data show that this material can be used for the all-fiber temperature sensors.

Enhancement of Red Upconversion Emission of ZnS: Er3+/Yb3+ Powders Synthesized via Solid Phase Reaction Method by Introducing Metal Fluoride

AbstractZnS: Er3+/Yb3+ powders were synthesized by a common solid phase reaction method with NaF, CaF2, LiF, AlF3 and MgF2 as dopant. The enhancement mechanisms of different metal fluorides (NaF, CaF2, LiF, AlF3 and MgF2) and concentrations (0 wt% ∼9 wt %) on structure, morphology and optical properties of ZnS: Er3+/Yb3+ powders were investigated systematically. The results revealed that as synthesized ZnS: Er3+/Yb3+ powders are main exhibited as wurtzite phase, the lattice constant, unit cell volume and lattice strain increase with metal fluoride codoping, which indicates the increase of resultant distortion. As synthesized ZnS: Er3+/Yb3+ powders have an intense red upconversion emission centered at 663 nm and a weak green upconversion emission centered at 567 nm under the excitation of a 980 nm laser diode. Compared with ZnS: Er3+/Yb3+ powders synthesized without metal fluoride, the upconversion emission intensities of ZnS: Er3+/Yb3+ powders synthesized with LiF, NaF, MgF2, AlF3 and CaF enhance ∼12 times, ∼9 times, ∼5 times, ∼3 times and ∼3 times, respectively. The strong red upconversion properties make the ZnS: Er3+/Yb3+ powders synthesized with metal fluoride a potential application in the field of light emitting diodes.

Biocompatible Yb3+/Er3+ Co-activated La2(WO4)3 Upconversion Nanophosphors for Optical Thermometry, Biofluorescent, and Anticancer Agents.

Non-cytotoxic upconversion nanocrystals are preferred candidates because they offer exceptional advantages for numerous applications, ranging from optical thermometry to bioimaging/biomedical applications. In this report, we demonstrate the luminescence characteristics and practical utility of a multifunctional upconversion nanophosphor based on Yb3+/Er3+:La2(WO4)3 (LWO) flakes. Strong upconversion green emission was observed from 6-mol % Er3+-doped LWO nanophosphor flakes excited by a 980 nm laser. We further enhanced the upconversion emission considerably by co-doping LWO nanophosphors with Yb3+/Er3+ to exploit energy migration from Yb3+ to Er3+ ions. The exceptional improvement in upconversion green and near-infrared emission was achieved by Yb3+ ion co-doping up to 6 mol %; beyond 6 mol %, emission intensities remarkably dropped due to concentration quenching. Photometric parameters were evaluated with and without Yb3+ ion-doped LWO nanophosphors, which exhibited a high green color purity of 95.6%, to elucidate their energy transfer mechanism. In addition, temperature-dependent upconversion emission trends were evaluated by analyzing the fluorescence intensity ratio, exhibiting higher temperature sensitivity than that previously reported. This suggests the applicability of our proposed nanophosphors to optical thermometry. As for bioimaging applications, the non-cytotoxicity of the optimized nanophosphor was confirmed based on distinct fluorescence images of a normal fibroblast cell line (L929). Furthermore, we demonstrated the strong cytotoxicity of nanophosphors against human colon cancer (HCT-116) cells. Based on the results, non-cytotoxic Yb3+(6 mol %)/Er3+ (6 mol %):LWO upconversion nanophosphor flakes are expected to be exceptional candidates owing to their extensive suitability to the fields of upconversion lasers, optical thermometry, and biomedical and anticancer applications. The results indicate the potential of upconversion materials in the effective execution of multiple strategic applications.

Dual-mode optical ratiometric thermometer based on rare earth ions doped perovskite oxides with tunable luminescence

Rare earth ions doped luminescent materials have drawn considerable attention as they can generate both upconversion and downshifting emissions. Here, the rare earth ions Pr3+/Er3+ codoped perovskite oxide Bi4Ti3O12 is proposed as a dual-mode temperature sensor and anti-counterfeiting material based on its up/down-conversion luminescence. Under 481 nm excitation, the intensity ratio of green emission (∼523 nm in Er3+) and red emission (∼611 nm in Pr3+) brings about a very high absolute sensitivity (Sa) of 2% K−1 at 568 K and a maximum relative sensitivity (Sr) of 1.03% K−1 at 478 K in the temperature range of 298–568 K. In addition, the upconversion green emissions of Er3+ yield a relatively-high Sr of 1.1% K−1 at 298 K with 980 nm excitation, which can provide self-calibration coupled with down-conversion luminescence temperature sensing mode. Besides, this phosphor also shows tunable luminous colors for the potential application in the anti-counterfeiting field under various excitation wavelengths.

Enhancement of green upconversion luminescence of Yb3+/Tb3+ co-doped BiOBr nanosheets and its potential applications in photocatalysis

In this work, a series of Yb3+/Tb3+ co-doped BiOBr nanosheets were synthesized by a simple solvothermal method, and the effect of Tb3+ and Yb3+ doping on the up-conversion (UC) luminescence was investigated. Under the excitation of 980 ​nm, BiOBr: Yb3+/Tb3+ nanosheets displayed emission bands at 494, 544, 584 and 622 ​nm arise from transitions 5D4 → 7FJ (J ​= ​6, 5, 4, 3) of Tb3+ ions, respectively. Furthermore, the concentration dependence of UC luminescence was comprehensively explored, and the BiOBr:15%Yb3+/3%Tb3+ nanosheets exhibited the most outstanding luminescent properties by the cooperative energy transfer. Moreover, the degradation rate of RhB by Yb3+/Tb3+ co-doped BiOBr reaches 98.9% for 30 ​min under full spectral irradiation, and 51.7% for 5 ​h under 980 ​nm irradiation, respectively. This work proves that Yb3+/Tb3+ co-doped BiOBr nanosheets have excellent green UC emission and have potential application in the field of near infrared activated photocatalysts.

Synthesis of highly luminescent β-NaYF4:Yb3+, Er3+ upconversion nanoparticles regulated by sodium hexametaphosphate: For customs supervision

Smuggling has caused serious adverse effects on the global market and national security, among which drug smuggling is increasingly rampant. Thus, the development of high-tech security strategies has become an urgent challenge for customs supervision. Recently, lanthanide ions (Ln3+) doped upconversion nanoparticles (UCNPs) have opened up new ways for security and anti-fake applications due to their unique optical properties under near-infrared excitation. Here, we propose a novel upconversion microcrystal composed of hexagonal phase NaYF4:Ln3+ capped by sodium hexametaphosphate (SHMP), successfully used in customs supervision. The addition of SHMP can not only regulate the morphology of microcrystals, but also significantly improve the luminescence properties of UC. The absolute quantum yield is up to 7% at the low power density of 30 W∙cm−2, above most currently reported levels. Without adding any organic additives, the precise control of particle phase and morphology (e.g., microrod, hexagonal prism and hollow sphere) would be achieved by adjusting the doping ratio of SHMP/Ln3+. As the reaction time extends, the morphology of NaYF4:Ln3+ changes from ellipsoid to microrod, while cubic phase transforms into hexagonal phase. Under the excitation of 980 nm laser, the green upconversion emission of hexagonal NaYF4:Ln3+ microrods is significantly strengthened, which is more powerful than other observed particles with other shapes. This strong upconversion emission that depends on morphology and phase has huge application potential in security anti-counterfeiting and photonic devices.

Self-doping induced oxygen vacancies and lattice strains for synergetic enhanced upconversion luminescence of Er3+ ions in 2D BiOCl nanosheets.

Rare earth (RE) ions combined with two-dimensional (2D) semiconductors can exhibit unexpected optical properties. However, fluorescence quenching has always been inevitable due to defects associated with the synthesis and doping of 2D materials. In this work, we reported an efficient upconversion (UC) enhancement of Er3+ doped BiOCl nanosheets, utilizing a defect engineering strategy conversely rather than eliminating defects. Experiments and theoretical calculations provide evidence that oxygen vacancies (OVs) and lattice strain are simultaneously formed in the BiOCl:Er3+ nanosheets through self-doping of Cl- ions. Under 980 nm excitation, samples doped with 300 mol% Cl- ions exhibit the best luminescent emission, and the green and red UC emissions are enhanced 3.5 and 15 times, respectively. We showed that the OVs in the 2D semiconductor can act as energy bridges to transfer charges to the Er3+ energy level, enriching the electron population at the excited levels; while, the lattice strain enhances the energy transfer and charge accumulation, which synergistically enhance the UC luminescence. This research provides a new insight into the development of defect engineering for UC PL in 2D nanomaterials.

A single-beam NIR laser-triggered full-color upconversion tuning of a Er/Tm:CsYb2F7@glass photothermal nanocomposite for optical security.

The development of advanced luminescent materials is highly desirable for addressing the rising threat of forgery. However, it is challenging to achieve stable full-color upconversion (UC) tuning in the same matrix upon a single-beam light excitation so as to ensure that authentic items are irreproducible. Herein, hexagonal Er/Tm:CsYb2F7 nanocrystals (NCs) embedded inorganic glass via an in situ crystallization strategy is fabricated, which can emit blue, cyan, green, yellow, orange, red and near-infrared (NIR) UC emissions by simply modifying an incident 980 nm laser power. This UC tuning is attributed to the combination roles of the highly efficient laser-induced photothermal effect of the CsYb2F7 host and simultaneous emissions of Er and Tm activators. Importantly, the robust inorganic glass matrix endows Er/Tm:CsYb2F7 NCs with excellent water resistance and the ability to withstand high-power laser irradiation. Based on these unique characteristics, a proof-of-concept anti-counterfeiting experiment is designed. The results indicate that dynamic full-color UC luminescence patterns can be easily tuned by simply changing the power of the incident 980 nm laser. The present work not only confirms that the designed photothermal material can increase information security, but also provides a new idea for practical applications in the field of anti-counterfeiting.

Hydrothermal synthesis of anisotropic SrGe4O9:Yb3+/Er3+ nanorods and optimized upconversion luminescence for optical temperature sensing

Anisotropic Yb3+/Er3+ co-doped SrGe4O9 nanorods were prepared for upconversion luminescence. The fluorescence intensity ratio (FIR) of the adjacent upconverted green emissions was applied to optical temperature measurement.

Highly efficient green up-conversion emission from fluoroindate glass nanoparticles functionalized with a biocompatible polymer.

Up-conversion nanoparticles have garnered lots of attention due to their ability to transform low energy light (near-infrared) into high-energy (visible) light, enabling their potential use as remote visible light nano-transducers. However, their low efficiency restricts their full potential. To overcome this disadvantage, fluoroindate glasses (InF3) doped at different molar concentrations of Yb3+ and Er3+ were obtained using the melting–quenching technique, reaching the highest green emission at 1.4Yb and 1.75Er (mol%), which corresponds to the 4S3/2 → 4I15/2 (540–552 nm) transition. The particles possess the amorphous nature of the glass and have a high thermostability, as corroborated by thermogravimetric assay. Furthermore, the spectral decay curve analysis showed efficient energy transfer as the rare-earth ions varied. This was corroborated with the absolute quantum yield (QY) obtained (85%) upon excitation at 385 nm with QYEr = 17% and QYYb = 68%. Additionally, InF3–1.4Yb–1.75Er was milled and functionalized using poly(ethylene glycol) to impart biocompatibility, which is essential for biomedical applications. Such functionalization was verified using FTIR, TG/DSC, and XRD.

Triplet-triplet annihilation photon upconversion from diphenylhexatriene and ring-substituted derivatives in solution.

We report that diphenylhexatriene (DPH) and its ring-substituted derivatives act as emitter molecules in triplet-triplet annihilation photon upconversion (TTA-UC). A palladium porphyrin derivative, meso-tetraphenyl-tetrabenzoporphine palladium complex (PdTPBP), which acts as a sensitiser in TTA-UC, and DPH derivatives were dissolved in tetrahydrofuran (THF). The solution showed blue-green to green UC emission under photoexcitation at 640 nm in a nitrogen atmosphere. The UC quantum efficiency (ηUC) values of the DPHs were estimated, with (E,E,E)-1,6-bis[4-(di-2-picolylamino)phenyl]hexa-1,3,5-triene (pico DPH) showing the highest. In addition, the quantum yields of triplet energy transfer (TET) and triplet-triplet annihilation (TTA), which are elementary processes in TTA-UC, were estimated, as well as the triplet lifetimes of each DPH derivative. The results indicate that the TTA process governs the value of ηUC.

Enhanced upconversion luminescence and optical temperature sensing performance in Er3+ doped BaBi2Nb2O9 ferroelectric ceramic

A series of BaBi 2- x Nb 2 Er x O 9 ceramic compositions with different Er 3+ concentration ( x = 0.0–8 mol %) is synthesized by a conventional solid-state reaction method. The upconversion (UC) light emission under 980 nm excitation with different pump powers and luminescence-based temperature sensing ability of BaBi 2- x Nb 2 Er x O 9 composition have been examined. The formation of a Bi-layered perovskite phase of BaBi 2 Nb 2 O 9 is confirmed having an orthorhombic geometry and Fmmm space group. Shifts in the Raman modes indicate reduced interaction of Bi 3+ ions with NbO 6 octahedron leading to relaxation of structural distortion with increasing Er 3+ content. The maximum value for remnant polarization and coercive field of doped BaBi 2- x Nb 2 Er x O 9 ceramic for ( x = 0.08) Erbium concentration comes out to be 2.9524 μC/cm 2 and 49.8980 kV/cm. For an optimum content of x = 0.04, two strong UC green emission bands were observed at 549 nm via 4 S 3/2 → 4 I 15/2 transition and 527 nm via 2 H 11/2 → 4 I 15/2 transitions, and a weak red emission appears at 657 nm attributed to the 4 F 9/2 → 4 I 15/2 transition. Pump power dependence suggests that UC emission is a two-photon mechanism for red and green emission bands. Temperature sensing evaluated by the change in the fluorescence intensity ratio (I 527 /I 549 ) indicates the highest sensitivity to be 0.00996 K −1 at 483 K for an optimum concentration of Er 3+ at x = 0.04 in BaBi 2- x Nb 2 Er x O 9 composition and is useful for non-contact optical thermometry.

Efficient Triplet-Triplet Annihilation Upconversion in Solution and Hydrogel Enabled by an S-T Absorption Os(II) Complex Dyad with an Elongated Triplet Lifetime.

A new Os(II) complex dyad featuring direct singlet-to-triplet (S-T) absorption and intramolecular triplet energy transfer (ITET) with lifetime up to 7.0 μs was designed to enhance triplet energy transfer efficiency during triplet-triplet annihilation upconversion (TTA-UC). By pairing with 9,10-bis(phenylethynyl)anthracene (BPEA) as a triplet acceptor, intense upconverted green emission in deaerated solution was observed with unprecedented TTA-UC emission efficiency up to 26.3% (with a theoretical maximum efficiency of 100%) under photoexcitation in the first biological transparency window (650-900 nm). Meanwhile, a 7.1% TTA-UC emission efficiency was acquired in an air-saturated hydrogel containing the photosensitizer and a newly designed hydrophilic BPEA derivative. This ITET mechanism would inspire further development of a highly efficient TTA-UC system for biological fields and renewable energy production.

Sol-gel synthesis and optical temperature sensing properties of PbTiO3:Yb3+/Er3+ phosphors

This paper reports a new type of PbTiO3:Yb3+/Er3+ (PTO:Yb3+/Er3+) phosphor synthesized by sol-gel method. Under 980 nm excitation, PTO:Yb3+/Er3+ phosphors exhibited green emission bands centered at 524/549 nm (2H11/2/4S3/2 → 4I15/2) and red emissions 661 nm (4F9/2 → 4I15/2). Concentration-dependent upconversion (UC) luminescence spectra showed that the optimal luminescence was observed at 6at%Yb3+/2at%Er3+-codoping concentration. A possible UC mechanism for PTO:Yb3+/Er3+ phosphor is discussed by the pump power-dependent UC luminescence spectra. The temperature-dependence (298–548 K) of the fluorescence intensity ratios (FIR) for the two green UC emission bands peaked at 524 and 549 nm was studied under a 980 nm laser excitation and the maximum relative sensitivity was approximately 12.25 × 10−3 K−1 at 298 K. The thermal quenching activation energy of near-infrared (NIR) luminescence was studied. It can be found that the phosphor has a small thermal quenching possibility and excellent thermal stability. The value of repeatability (R) more than 98% has obtained via four cycles of cooling and heating, which prove that the phosphor has a good cycling stability. These results indicate that PTO:Yb3+/Er3+ phosphor is a promising candidate for optical temperature sensors with high sensitivity and good repeatability.

Study of near-infrared induced color tunability and optical bistability in Ho3+/Yb3+ codoped YV0.75Ta0.25O4 phosphor

This work reports the green to red color tunable upconversion emission in a newly synthesized Ho3+/Yb3+ codoped YV0.75Ta0.25O4 phosphor, prepared by solid-state reaction (SSR) method. The crystal phase formation has been confirmed by X-Ray diffraction analysis. The Fourier transform infrared (FTIR) spectrum show bands at different frequencies due to V-O and Ta-O, and found to play a vital role in relaxation (radiative and non-radiative) processes. The synthesized phosphor sample show intense upconversion (UC) emission in green (∼539 nm), red (∼659 nm) and in near infrared (NIR∼ 754 nm) regions on 980 nm laser excitation. These bands appear as a result of (5F4+5S2→5I8), (5F5→5I8) and (5F4+5S2→5I7) transitions of Ho3+ ion, respectively. The tunability in color from green to orange-red is observed on varying the pump power of NIR laser (980 nm excitation). The intrinsic optical bistability is observed in both, green & red upconversion bands with the increase and decrease in power of NIR source. The Ln I-Ln P plots suggest that green & red UC emissions are due to two photon absorption at low laser power. A decrease in the slope values at higher pump powers confirms the laser induced optical heating (LIOH) in the material. The pump power based color tunable emission and optical bistability can be utilized in security detection, optical memory, optical color coding, color switching and in various advanced applications.