PROJECT DURATION:           October 2015 - September 2017
DURATA PROIECTULUI:        Octombrie 2015 - Septembrie 2017

PROJECT LEADER:              National Institute for Laser, Plasma and Radiation Physics, Magurele, Bucharest, Romania
CONDUCATOR PROIECT:      Institutul National de Cercetare-Dezvoltare pentru Fizica Laserilor, Plasmei si Radiatiei, Magurele, Bucuresti, Romania

Contract value:                      550.000 lei

Valoare contract:                   550.000 lei

The research team:                GHEORGHE Cristina Petruta, PhD

Echipa de cercetare:              GHEORGHE Lucian Marian, PhD

                                            TOMA Octavian, PhD

                                            ACHIM Alexandru, PhD

                                            VOICU Flavius Marian, PhD student

                                            HAU Stefania, PhD student

                                            CROITORU Gabriela, PhD student

                                            CHIRCUS Laurentiu, sub-engineer 

___________________________________________________________________________________________________________________________________________________________________________

ABSTRACT. Based on the most recent fundamental and technological advances, the project aims to identify and develop new laser materials with controllable properties for efficient generation of laser emission in the visible (VIS) spectral range. The research will be directed toward calcium-niobium-gallium-garnet (CNGG) and calcium-lithium-niobium-gallium- garnet (CLNGG) intrinsic disordered materials, as single crystals and alternative polycrystalline ceramic materials, mainly doped with RE3+ ions (RE = Pr, Sm, Tb, Dy) and sensitized with appropriate lanthanide ions.

______________________________________________________________________________________________________________________________________________________

2015. Value: 30.000 lei
Objective I. Disordered RE³⁺-doped and sensitized CNGG and CLNGG single crystalline laser materials. / Preliminary.
Objective II. Disordered RE³⁺-doped and co-doped CNGG and CLNGG polycrystalline laser ceramics. / Preliminary.

2016. Value: 350.000 lei
Objective I. Disordered RE³⁺-doped and sesitized CNGG and CLNGG single crystalline laser materials. / Partially.
Objective II. Disordered RE³⁺-doped and co-doped CNGG and CLNGG polycrystalline laser ceramics. / Partially.

2017. Value: 170.000 lei
Objective I. Disordered RE³⁺-doped and sesitized CNGG and CLNGG single crystalline laser materials. / Final.
Objective II. Disordered RE³⁺-doped and co-doped CNGG and CLNGG polycrystalline laser ceramics. / Final.
______________________________________________________________________________________________________________________________________________________

RESULTS IN 2015
Objective I. Disordered RE³⁺-doped and sensitized CNGG and CLNGG single crystalline laser materials. / Preliminary.
Objective II. Disordered RE³⁺-doped and co-doped CNGG and CLNGG polycrystalline laser ceramics. / Preliminary.

Activities:
I.1 High-resolution spectroscopic characterization. / Preliminary results.

Obtained results:
During this stage were achieved all the objectives and activities specified in the project. We have identified new luminescent systems based on the emission in the visible domain of RE3+ (Sm, Dy, Pr, Tb) ions doped in host materials with intrinsic disorder, type garnet calcium-niobium-gallium (CNGG) and calcium-lithium-niobium-gallium (CLNGG).
Thus:
● Samples of CNGG and CLNGG doped with Sm (0.1, 1 and 3 at.%), Dy (0.1, 1 and 3 at.%), Pr (0.1, 1 and 3 at.%) and Tb (0.1, 1 and 3 at.%) ions, using solid state reaction technique.
● Based on high-resolution spectroscopic measurements at 300 and 10 K (absorption, emission and emission kinetics) new spectral data about these ions RE³⁺ (Sm, Dy, Pr, Tb) doped CNGG and CLNGG were obtained.
● The obtained preliminary spectral data confirms that selected doped ions have been successfully incorporated into the proposed materials, allowing us to continue the research with the growth of the single crystals and obtaining the ceramics of CNGG and CLNGG doped RE³⁺ (Sm, Dy, Pr, Tb).

● Raportul stiintific pe anul 2015 este disponibil aici: | 2015 | 
____________________________________________________________________________________________________________________________________________________________________________

RESULTS IN 2016
Objective I. Disordered RE³⁺-doped and sesitized CNGG and CLNGG single crystalline laser materials. / Partially.
Objective II. Disordered RE³⁺-doped and co-doped CNGG and CLNGG polycrystalline laser ceramics. / Partially.

Activities:
I.1 Single crystals growth by Czochralski method.
I.2 High resolution optical spectroscopy characterization.
I.3 Optimization of visible laser emission.
II.1 Obtaining of polycrystalline transparent ceramics.
II.2 High resolution optical spectroscopy characterization.

Obtained results
During this stage were achieved all the objectives and activities specified in the project.
● Single crystals of Sm:CNGG and Sm:CLNGG with 3.4 and 5 at.% Sm³⁺ ions and Dy:CNGG and Dy: CLNGG with 3.4 and 5 at.% Dy³⁺ ions were grown by Czochralski method.
● Ceramics samples of CNGG and CLNGG doped with Sm (0.1, 1 and 3 at.%) ions, were obtained using vacuum reactive sintering method.
● Ceramics samples of CNGG and CLNGG doped with Sm³⁺ ions and sensitized with Ce³⁺ ions with different concentration of doping ions were obtained using solid state reaction technique.
● Ceramics samples of CNGG and CLNGG doped with Dy³⁺ ions and sensitized with Ce³⁺ ions with different concentration of Ce³⁺ ions were obtained using solid state reaction technique.
● High resolution optical spectroscopy at different temperature was applied to obtain static and dynamic properties of Sm³⁺ ions doped CNGG and CLNGG single crystals. The absorption spectra of Sm³⁺ at room temperature were analyzed on the basis of the Judd-Ofelt theory in order to calculate the line strengths of Sm³⁺ electric dipole transitions. The intensity J-O parameters obtained for Sm doped both crystals were estimated and used to determine the radiative transition rates, fluorescence branching ratios and radiative lifetime. Partial energy levels of Sm³⁺ have been established based on the low temperature absorption and emission spectra. The experimentally integrated cross-sections for the ⁴G_5/2→⁶H_7/2 transition at 615 nm were fund to be 0.87×10^-21 cm² for CNGG and 1×10^-21 cm² in the case of CLNGG.
● High resolution optical spectroscopy at different temperature was applied to obtain static and dynamic properties of Dy³⁺ ions doped CNGG and CLNGG single crystals. Partial energy levels of Dy³⁺ have been established based on the low temperature absorption and emission spectra.
● Ceramic samples of CLNGG doped with 0.1 at. % Sm ions and co-doped with 0.01 - 0.1 at.% Ce³⁺ ions were prepared and investigated to establish Ce³⁺ ions concentration in order to obtain efficient energy transfer from Ce→Sm and increase the emission of Sm ions in visible domain. The emission spectra of (x Ce, 0.01 Sm):CLNGG at room temperature were analyzed and was established that CLNGG sample doped with of 0.1 at.% Sm + 0.02 at.% Ce had the most intense Sm³⁺ emission lines.
● Ceramic samples of CLNGG doped with 0.02 at.% Ce and co-doped with 1 - 10 at % Sm were prepared and investigated in order to establish the best Sm³⁺ ions concentration before concentration quenching mechanism appear. The emission spectra of (0.02 Ce, x Sm):CLNGG at room temperature were analyzed and was established that CLNGG sample doped with of 0.02 at.% Ce + 3 at.% Sm had the most intense Sm³⁺ emission lines.
● Ceramic samples of CLNGG doped with 0.1 at.% Dy³⁺ ions and co-doped with 0.01 - 0.1 at.% Ce ions were prepared and investigated to establish Ce³⁺ ions concentration in order to obtain efficient energy transfer from Ce→Dy and increase the emission of Dy³⁺ ions in visible (blue and yellow) domain. The emission spectra of (x Ce, 0.01 Dy):CLNGG at room temperature were analyzed and was established that CLNGG sample doped with of 0.1 at.%Dy + 0.9 at.% Ce had the most intense Dy³⁺ emission lines.
● Raportul stiintific pe perioada 2015-2016 este disponibil aici: | 2016 | 

____________________________________________________________________________________________________________________________________________________________________________

Activities
I.1     Single crystals growth by Czochralski method.
I.2     High resolution optical spectroscopy characterization.
I.3     Optimization of visible laser emission.
II.1    Obtaining of polycrystalline transparent ceramics.
II.2    High resolution optical spectroscopy characterization.
II.3    Optimization of visible laser emission. / Partial
II.4    Optimization of visible laser emission. / Final

Rezultate etapa
- Probe monocristaline si ceramici policristaline de tip CNGG si CLNGG co-dopate cu ioni RE³⁺ pentru masuratori spectroscopice;
- Montaje si date spectrale noi;
- Modelarea datelor si determinarea parametrilor caracteristici;
- Date noi spectrale si de cinetica emisiei.
- Analiza matematica a datelor experimentale.
- Evaluarea eficientei de emisie laser in sisteme sensibilizate.
- Sinteza datelor in vederea publicarii in reviste cotate ISI.
- Prezentarea rezultatelor la Conferinte Internationale si publicarea in reviste cotate ISI.

DISSEMINATION OF THE RESULTS

I. ARTICLES PUBLISHED IN ISI JOURNALS
1. C. Gheorghe, A. Lupei, S. Hau, F. Voicu, L. Gheorghe, A. M. Vlaicu, "Compositional dependence of optical properties of Sm³⁺-doped Y₃Sc_XA_l5-XO₁₂ polycrystalline ceramics," J. Alloys & Comp. 683, 547-553 (2016). IF 3.014.
2. C. Gheorghe, S. Hau, L. Gheorghe, F. Voicu, M. Greculeasa, A. Achim, M. Enculescu, “Optical properties of Sm³⁺ doped Ca₃(Nb,Ga)₅O₁₂ and Ca₃(Li,Nb, Ga)₅O₁₂ single crystals,” J. Lumin. 186, 175-182 (2017). IF = 2.693.
3. I.О. Vorona, R.P. Yavetskiy, A.G. Doroshenko, S.V. Parkhomenko, A.V. Tolmachev, V.N. Baumer, D.Yu. Kosyanov, V.I. Vovna, V.G. Kuryavyi, M. Greculeasa, L. Gheorghe, S. Hau, C. Gheorghe, G. Croitoru, “Structural-phase state and lasing of 5-15 at% Yb³⁺:Y₃Al₅O₁₂ optical ceramics,” J. Eur. Cer. Soc. 37(13) (2017) 4115-4122. IF = 3.411.

II. COMMUNICATIONS AT INTERNATIONAL CONFERENCES

1. F. Voicu, L. Gheorghe, M. Greculeasa, A. Achim, C. Gheorghe, S. Hau, “Growth and optical properties of Sm³⁺ doped Ca₃(Nb,Ga)₅O₁₂ and Ca₃(Li,Nb, Ga)₅O₁₂ single crystals,” TIM 17 Physics Conference, 25 - 27 May 2017, Timisoara, Romania; poster CM-P08.
2. S. Hau, C. Gheorghe, L. Gheorghe, I. Porosnicu, A. Crisan, “Luminescence properties and energy transfer of Sm³⁺ and Dy³⁺ co-doped Ca₃(Li,Nb, Ga)₅O₁₂: Ce³⁺ novel phosphors under UV excitation,” Timisoara, Romania, 25-27 Mai 2017; poster P02.
3. L. Gheorghe, F. Voicu, M.Greculeasa, A. Achim, F. Khaled, P. Loiseau, G. Aka, S. Hau, C.Gheorghe, G Croitoru, “Pure and Yb-doped La_xGdySc_4-x-y(BO₃)₄ incongruent borates type crystal: czochralski growth, nonlinear properties and laser performances,” TIM 17 Physics Conference, 25 - 27 May 2017, Timisoara, Romania; invited talk CM-I01.
4. I. O. Vorona, R.P. Yavetskiy, M.V. Dobrotvorskaya, A.G. Doroshenko, S.V. Parkhomenko, A.V. Tolmachev, L. Gheorghe, C. Gheorghe, S. Hau, “Solid-state sintering and luminescent properties of Yb³⁺, Er³⁺:YAG transparent ceramics,” International Conference on Oxide Materials for Electronic Engineering - Fabrication, Properties and Applications, OMEE-2017, May 29 - June 2, 2017, Lviv, Ukraine; poster Mo-P59.
5. I. O. Vorona, R. P. Yavetskiy, A. G. Doroshenko, S. V. Parkhomenko, A. V. Tolmachev, L. Gheorghe, M. Greculeasa, C. Gheorghe, S. Hau, and G. Croitoru, “Nd³⁺:YAG Ceramic Materials with Efficient Laser Emission under Diode-Laser Pumping,” LIC 2017, 20-23 June 2017, Bucharest, Romania; poster LWA5.4.