Manoj Kumar Mahata

Structural and optical properties of Er3+/Yb3+ doped barium titanate phosphor prepared by co-precipitation method

In the present work we have synthesized the Er(3+)/Yb(3+) codoped barium titanate phosphor via co-precipitation method and studied its upconversion emission properties. The prepared BaTiO3 powder was found in cubic phase as a major component and having good crystallinity revealed by the XRD analysis. Optical band gap of the cubic barium titanate was calculated using the diffuse reflectance absorption spectrum. Good green upconversion emission is observed from the samples when excited by 980 nm diode laser. The variation in upconversion emission intensity is studied with the increase in excitation power as well as temperature of the sample. It is found that the emission bands centred at 524 and 548 nm are thermally coupled and can act as a temperature sensor in the 300-480 K temperature range.

Enhanced temperature sensing response of upconversion luminescence in ZnO–CaTiO3: Er3+/Yb3+ nano-composite phosphor

Upconversion emission and temperature sensing of the Er(3+)/Yb(3+) doped ZnO-CaTiO3 nano-composite phosphor is studied by varying the ZnO concentration. The XRD and EDX studies reveal the formation of composite phase when ZnO doping exceeds above 10 mw%. Five prominent upconversion emission bands at 410, 492, 524, 545 and 662 nm corresponding to (2)H9/2→(4)I15/2, (4)F3/2→(4)I15/2, (2)H11/2→(4)I15/2, (4)S3/2→(4)I15/2 and (4)F9/2→(4)I15/2 transitions, respectively are found under 980 nm excitation from a diode laser. On the basis of rise time analysis it was found that energy transfer process is responsible for the intense upconversion emission. Large reduction in decay time of (4)S3/2 level is observed on the ZnO incorporation in host matrix. Moreover, the absolute sensor sensitivity, relative sensor sensitivity and calculated color coordinates of the samples are also determined. These results indicate the potentiality of this composite phosphor for various applications.

Demonstration of Temperature Dependent Energy Migration in Dual-Mode YVO 4 : Ho 3+ /Yb 3+ Nanocrystals for Low Temperature Thermometry

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

Dualistic temperature sensing in Er3 +/Yb3 + doped CaMoO4 upconversion phosphor

Temperature sensing performance of Er3+/Yb3+ doped CaMoO4 phosphor prepared via polyol method is reported herein. The X-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy are done to confirm the phase, structure and purity of the synthesized phosphor. The infrared to green upconversion emission is investigated using 980nm diode laser excitation along with its dependence on input pump power and external temperature. The temperature dependent fluorescence intensity ratio of two upconversion emission bands assigned to 2H11/2→4I15/2 (530nm) and 4S3/2→4I15/2 (552nm) transitions has shown two distinct slopes in the studied temperature range - 300 to 760K and therefore, dual nature of temperature sensitivity is observed in this phosphor. This phenomenon in rare earth doped materials is either scarcely reported or overlooked. The material has shown higher sensitivity in the high temperature region (535K<T<760K) with a maximum of 7.21×10-3K-1 at 535K. The results indicate potential of CaMoO4: Er3+/Yb3+ phosphor in high temperature thermometry.

Enhancement of upconversion, temperature sensing and cathodoluminescence in the K+/Na+ compensated CaMoO4:Er3+/Yb3+ nanophosphor

Charge compensated alkali metal ions (Na+, K+) codoped CaMoO4:Er3+/Yb3+ nano-flakes were synthesized via a hydrothermal method. The effect of doping concentration of Na+ and K+ ions on upconversion luminescence in CaMoO4:Er3+/Yb3+ was investigated with respect to its dependence on input pump power and external temperature using 980 nm laser light excitation. Simultaneous incorporation of K+/Na+ into CaMoO4:Er3+/Yb3+ showed 36 and 5 times enhancements in green and red emission intensities, which were explained in terms of charge compensation and lifetime variation in the 4S3/2 and 4F9/2 levels of Er3+ ions. A high thermal sensitivity of the material was realized with K+/Na+ incorporation using the fluorescence intensity ratio technique of two thermally coupled energy levels (2H11/2 & 4S3/2) of Er3+. The temperature sensitivity was enhanced by four times by K+/Na+ codoping with a maximum sensitivity of 0.0216 K−1 at 490 K. Additionally, the cathodoluminescence properties of the material as a function of filament current and accelerating voltage were also explored and showed enhanced luminescence, which is suitable for field emission display device applications. The results show that simultaneous codoping of K+/Na+ in CaMoO4:Er3+/Yb3+ is a very effective way to integrate this material for advanced photonic applications.

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

A series of Er3+–Yb3+ doped gadolinium molybdate phosphors were synthesized via hydrothermal method with varying Er3+ and Yb3+ concentrations and their thermal stability, crystal phase formation, particle morphology and photoluminescence properties were explored. The effects of rare earth doping concentration and annealing temperature on upconversion and downconversion properties have been investigated upon 980 nm and 380 nm light excitation and explained with the variation in lifetime of the 4S3/2 level of Er3+. The materials were further investigated to look into the effect of Er3+-concentration on optical temperature sensing and nano-heating behavior. Temperature sensing measurements were performed by the fluorescence intensity ratio technique using the transitions from the two thermally coupled energy levels (2H11/2/4S3/2 → 4I15/2) of Er3+. The maximum temperature sensitivity was obtained as 0.0105 K−1 (at 450 K), which is among the highest measured sensitivities for luminescence based thermometers. Moreover, the material shows very high thermal gain due to laser irradiation, resulting in a temperature rise from 364 K to 683 K as the excitation power changes from 7.0 to 65 W cm−2 and defines the present material as a highly sensitive thermographic phosphor. Additionally, the paramagnetic nature and effect of the magnetic field on upconversion properties of this phosphor have also been explored. The thermally-stable, paramagnetic Gd2Mo3O9: Er3+/Yb3+ phosphor particles seem to be potential candidates for displays, remote temperature sensing, optical heaters, magneto-optic modulators and bio-imaging applications.

Er3+, Yb3+ doped yttrium oxide phosphor as a temperature sensor

The rare earth ions doped upconversion phosphors as temperature sensor need intensive investigation because of its wide range of potential applications. Here the Y2O3:Yb3+,Er3+ phosphor is synthesized via combustion synthesis and its upconversion emission is studied using 976 nm diode laser excitation source. The emission band intensities at 522 and 550 nm are found to be thermally coupled and it leads to conclude that the sample can act as a temperature sensor.

Photon-Upconverting Materials: Advances and Prospects for Various Emerging Applications

Rare-earth-doped upconversion materials, featuring exceptional photophysical properties including long lifetime, sharp emission lines, large anti-Stokes shift, low autofluorescence of the background, and low toxicity, are promising for many applications. These materials have been investigated extensively since the 1960s and employed in many optical devices. However, due to rapid development of synthesis strategies for nanomaterials, upconversion materials have been rehighlighted on the basis of nanotechnology. Herein, we discuss the recent advances in upconversion materials. We start by considering energy transfer processes involved in the basic study of upconversion emission phenomena, as well as synthesis strategies of these materials. Progress in different energy transfer processes, which play an important role in determining luminescence efficiency, is then discussed. Newer applications of these materials have been vastly reviewed.

Upconversion emission study of Er3+ doped CaMoO4 phosphor

The infrared to visible upconversion emission in Er3+ doped CaMoO4 phosphor has been investigated upon 980 nm diode laser excitation. The X-ray dffraction analysis reveals well crystalline nature and tetragonal phase structure of the prepared phosphor annealed at 800 °C. The Er3+ doped CaMoO4 phosphor has shown intense green upconversion emission upon 980 nm didode laser excitation. The green emission bands at 530 nm and 552 nm corresponds to the 2H11/2→4I15/2 and 4S3/2→4I15/2 electronic transitions, respectively of Er3+ ion. The very weak red emission band around 656 nm is assigned to the 4F9/2→4I15/2 transition of Er3+ ion. The CIE color coordinate exhibits the emission color in intense green region, indicating the use of present phosphor in display device applications.

Upconversion Luminescence Sensitized pH-Nanoprobes

Photon upconversion materials, featuring excellent photophysical properties, are promising for bio-medical research due to their low autofluorescence, non-cytotoxicity, low photobleaching and high photostability. Upconversion based pH-nanoprobes are attracting considerable interest due to their superiority over pH-sensitive molecular indicators and metal nanoparticles. Herein, we review the advances in upconversion based pH-nanoprobes, the first time in the seven years since their discovery in 2009. With a brief discussion on the upconversion materials and upconversion processes, the progress in this field has been overviewed, along with the toxicity and biodistribution of upconversion materials for intracellular application. We strongly believe that this survey will encourage the further pursuit of intense research for designing molecular pH-sensors.