Synthesis, structure, Stokes and anti-Stokes visible luminescence of Tm3+–Yb3+ co-doped Lu3Sc2Ga3O12 nanorods

Ramadevi N.,Praveena R.,Venkatramu V.,Basavapoornima Ch.,Lavín V.,Joshi B.D. 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.10

Lu3Sc2Ga3O12 garnet nanorods co-doped with Tm3+ and Yb3+ optically active ions have been synthesized by Pechini sol– gel method, and their structural, morphological and luminescence properties have been explored. X-ray difraction pattern confrmed that the synthesized Lu3Sc2Ga3O12 nanomaterials were crystallized in cubic garnet structure with an average crystallite size of 30 nm. Morphology of these powders confrmed the formation of rods with an average length of 8 μm and diameter of 90 nm. The difuse refectance spectra were used to obtain partial energy-level structure of Tm3+ and Yb3+ ions in Lu3Sc2Ga3O12 nanorods. Intense blue Stokes luminescence of Tm3+ ions at around 454 nm, under 360 nm ultraviolet excitation, as well as anti-Stokes luminescence at around 483 nm and co-operative luminescence at 490 nm, under near-infrared 980 nm excitation, have been measured. The intensity of these peaks increased with increasing of Yb3+ concentration up to 5 mol% and then decreased due to energy transfer between optically active ions. In addition, luminescence at ~ 545 and 565 nm has been observed in the anti-Stokes spectra which is due to the energy transfer from Ln3+ ions to the impurities such as Er3+ and Ho3+ ions. Laser pump power-dependent luminescence spectra confrmed that three photons were involved to populate the 1 G4 level in the upconversion mechanism. Luminescence decay curves have been measured for 1 D2 level and have been found to be non-exponential with an average lifetime of 20 μs. The non-exponential nature of decay curves is ascribed to energy transfer among Tm3+ ions through cross-relaxation processes. Colour co-ordinates of the samples excited at 980 nm lie in the blue–green region and also near to the white light region in the CIE diagram. All these results indicate that the present garnet nanorods could be a promising optically active material for the solid-state display devices.

Optical Absorption and EPR Studies on Gamma-Ray Irradiated RE3+-Doped Fluorophosphate Glasses

Linganna, K.,Ju, S.,Basavapoornima, Ch.,Jayasankar, C. K.,Venkatramu, V.,Kim, C. J.,Han, W.-T. Springer-Verlag 2018 Journal of inorganic and organometallic polymers a Vol.28 No.3

Spectroscopic Properties of Yb³⁺-Doped Silicate Glasses

Linganna, Kadathala,Ju, Seongmin,Kim, Bokhyeon,Han, Won-Taek,Venkatramu, Vemula,Jayasankar, Chalicheemalapalli Kulala De Gruyter 2018 Zeitschrift für physikalische Chemie Vol.232 No.1

<P><B>Abstract</B></P><P>Yb<SUP>3+</SUP>-doped silicate glasses (SiO<SUB>2</SUB>–Nb<SUB>2</SUB>O<SUB>5</SUB>–K<SUB>2</SUB>O–ZnF<SUB>2</SUB>) were prepared by a conventional melt quenching technique and their spectroscopic properties were investigated. The emission cross-section was found to be 0.53×10<SUP>−20</SUP>cm<SUP>2</SUP>at 1006 nm from the reciprocity method described by McCumber from the measured absorption spectrum of 1.0 mol% Yb<SUB>2</SUB>O<SUB>3</SUB>-doped glass. The lifetime (<I>τ</I><SUB>exp</SUB>) and figure of merit (<I>σ<SUB>em</SUB></I>×<I>τ</I><SUB>exp</SUB>) for the<SUP>2</SUP>F<SUB>5/2</SUB>→<SUP>2</SUP>F<SUB>7/2</SUB>transition of 1.0 mol% Yb<SUB>2</SUB>O<SUB>3</SUB>-doped silicate glass, were evaluated to be 0.50 ms and 0.26 cm<SUP>2</SUP>ms, respectively. The other spectroscopic parameters,<I>β</I><SUB>min</SUB>,<I>I</I><SUB>sat</SUB>and<I>I</I><SUB>min</SUB>were found to be 0.17, 29.00 kW/cm<SUP>2</SUP>and 4.90 kW/cm<SUP>2</SUP>, respectively. The results indicate that the present Yb<SUP>3+</SUP>-doped silicate glasses could be useful as laser gain media at 1006 nm.</P>

Photon avalanche upconversion in Ho³⁺-Yb³⁺ co-doped transparent oxyfluoride glass-ceramics

Babu, P.,Martin, I.R.,Venkata Krishnaiah, K.,Seo, H.J.,Venkatramu, V.,Jayasankar, C.K.,Lavin, V. North Holland 2014 Chemical physics letters Vol.600 No.-

The Ho<SUP>3+</SUP>-Yb<SUP>3+</SUP> co-doped transparent glass and glass-ceramics containing CaF<SUB>2</SUB> nanocrystals have been prepared. Differential thermal analysis and X-ray diffraction measurements have been made to characterize thermal properties of glass and structural changes in glass-ceramics, respectively. Photon avalanche upconversion has been achieved by exciting the samples at 745nm at room temperature. An intense green and a weak red upconverted emissions corresponding to the <SUP>5</SUP>S<SUB>2</SUB>:<SUP>5</SUP>F<SUB>4</SUB>→<SUP>5</SUP>I<SUB>8</SUB> and <SUP>5</SUP>F<SUB>5</SUB>→<SUP>5</SUP>I<SUB>8</SUB> transitions, respectively, have been observed. The upconversion intensity has been found to increase with the increase in the size of the fluoride nanocrystals in glass-ceramics. Experimental evidences confirm that the mechanism of upconversion is photon avalanche.

Visible upconversion in Er³⁺/Yb³⁺ co-doped LaAlO₃ phosphors

Singh, Vijay,Rai, V.K.,Singh, N.,Pathak, M.S.,Rathaiah, M.,Venkatramu, V.,Patel, Rahul V.,Singh, Pramod K.,Dhoble, S.J. Elsevier 2017 Spectrochimica acta. Part A, Molecular and biomole Vol.171 No.-

<P><B>Abstract</B></P> <P>The Er<SUP>3+</SUP> doped and Er<SUP>3+</SUP>/Yb<SUP>3+</SUP> co-doped LaAlO<SUB>3</SUB> phosphors have been synthesized by the combustion method and characterized their structural, morphological, elemental, vibrational and optical properties. The optical absorption and upconversion properties of the synthesized phosphors have been studied. Upon co-doping Yb<SUP>3+</SUP> ions into Er<SUP>3+</SUP>:LaAlO<SUB>3</SUB>, the blue, green and red upconversion emissions of Er<SUP>3+</SUP> ions have been enhanced about ~20, ~54 and ~22 times, under 978nm laser excitation. The observed upconversion emissions could be due to excited state absorption in Er<SUP>3+</SUP>:LaAlO<SUB>3,</SUB> whereas energy transfer is dominant mechanism in Er<SUP>3+</SUP>/Yb<SUP>3+</SUP>:LaAlO<SUB>3</SUB> phosphors. The tuning in the color emitted from the synthesized phosphors towards the green region has been found due to incorporation of the Yb<SUP>3+</SUP> ions. With increase in the pump power, the color emitted from the co-doped phosphor is not tuned significantly, showing its applicability in making the green display devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> By facile combustion synthesis, Er<SUP>3+</SUP> and Er<SUP>3+</SUP>/Yb<SUP>3+</SUP> doped LaAlO<SUB>3</SUB> phosphors are obtained. </LI> <LI> Phosphor was characterized using XRD, SEM-EDX, FTIR and Up-conversion spectroscopy. </LI> <LI> Upon excitation at 978nm, intense up-conversion emission is observed. </LI> <LI> Prepared materials could be suitable for up-conversion lasers and green display device. </LI> </UL> </P> <P><B>Graphical Abstract</B></P> <P>[DISPLAY OMISSION]</P>

1.53 μm luminescence properties of Er³⁺-doped K-Sr-Al phosphate glasses

Linganna, K.,Rathaiah, M.,Vijaya, N.,Basavapoornima, Ch.,Jayasankar, C.K.,Ju, S.,Han, W.T.,Venkatramu, V. Ceramurgica ; Elsevier Science Ltd 2015 CERAMICS INTERNATIONAL Vol.41 No.4

<P>Trivalent erbium (Er3+)-doped K-Sr-Al phosphate glasses were prepared and studied their spectroscopic properties as a function of Er2O3 concentration. Judd-Ofelt analysis has been carried out for 1.0 mol% Er2O3-doped phosphate glass and in turn radiative properties have been evaluated for the excited levels of Er3+ ion. The radiative lifetime for the (4)t(13/2) level was found to be higher for the present glass when compared to other Er3+-doped glasses. The Er3+-doped glasses exhibit intense near infrared emission at 1.53 mu m corresponds to I-4(13/2)-> I-4(15/2) transition as well as green emission at 546 nm corresponding to S-4(3/2)-> I-4(15/2) under 980 nm and 488 nm excitations, respectively. The emission cross-section spectrum for 1.0 mol% of Er2O3-doped glass has been evaluated using McCumber theory. The gain cross-section has been evaluated as a function of population inversion, which revealed that the lasing action would be achieved at 1.53 mu m for a population inversion about 40%. Decay curves for the I-4(13/2) level were measured and lifetimes have been determined for the studied glasses. The results indicate that the present glasses could be useful for laser as well as optical amplifiers at 1.53 mu m. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.</P>

Dysprosium doped niobium zinc fluorosilicate glasses: Interesting materials for white light emitting devices

Prabhakar, J.,Kummara, Venkata Krishnaiah,Linganna, K.,Babu, P.,Jayasankar, C.K.,Kim, Jihoon,Venkatramu, V. Elsevier 2019 OPTIK -STUTTGART- Vol.176 No.-

<P><B>Abstract</B></P> <P>Trivalent dysprosium doped niobium zinc fluorosilicate glasses modified with different Nb<SUB>2</SUB>O<SUB>5</SUB>/ZnF<SUB>2</SUB> molar (M) ratios have been fabricated by the traditional melt-quenching technique and derived their structural, photoluminescence and decay properties using spectroscopic techniques. Induced structural modifications have been observed upon increasing content of Nb<SUB>2</SUB>O<SUB>5</SUB>. Maximum phonon energy of the glass matrix is found to be 1010 cm<SUP>−1</SUP> from the Raman spectrum. The emission spectra of these glasses exhibit two intense bands at 480 and 570 nm besides a weak red emission at 650 nm. The decay profiles of Dy<SUP>3+</SUP> ion for the <SUP>4</SUP>F<SUB>9/2</SUB> level exhibit a non-exponential behavior for all the glasses. The intrinsic lifetimes for the <SUP>4</SUP>F<SUB>9/2</SUB> level of Dy<SUP>3+</SUP> ion have been determined by using the Inokuti-Hirayama model and are found to be 409, 366 and 325μs for the glasses with Nb<SUB>2</SUB>O<SUB>5</SUB>/ZnF<SUB>2</SUB>:10/30, 20/20 and 30/10 M ratios, respectively. The color coordinates have been evaluated from the emission spectra of the glasses and found that the glass with Nb<SUB>2</SUB>O<SUB>5</SUB>/ZnF<SUB>2</SUB>:30/10 M ratio appears near to the equal energy point. The correlated color temperature matches well to the summer sunlight region (4900–5600 K), indicating that the glasses could be a potential candidate for white light emitting devices.</P>

Luminescence properties of Lu3Al5O12:Tb3+ nano-garnet

Praveena, R.,Shim, Jae Jeong,Cai, Peiqing,Seo, Hyo Jin,Chung, Wan-Young,Kwon, Tae Ha,Jayasankar, C. K.,Haritha, P.,Venkatramu, V. Korean Physical Society 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.12

Trivalent terbium-doped lutetium-aluminate nano-garnet (Lu3Al5O12:Tb3+) powder was prepared by using the Pechini sol-gel process. The structure and crystallinity of the Lu3Al5O12:Tb3+ nano-garnet were characterized by using X-ray diffraction, transmission electron microscopy and Fourier transform infrared spectroscopy. The green emission of Tb3+ ions is observed at 545 nm corresponding to the D-5(4) -> F-7(5) transition under the 271-nm excitation. The temperature dependent luminescence properties of the Lu3Al5O12:Tb3+ nano-garnet are investigated. The results show that the present garnet exhibits better thermal stability than the other green emitting phosphors, hence, the Lu3Al5O12:Tb3+ phosphor is a promising candidate for light-emitting devices.