PROIECT DE CERCETARE POSTDOCTORALA PD-159/2010
PROGRAMUL "RESURSE UMANE"

FINANTARE :                         CONSILIUL NATIONAL AL CERCETARII STIINTIFICE DIN INVATAMANTUL SUPERIOR (CNCSIS), BUCURESTI, ROMANIA
FUNDED BY:                         NATIONAL COUNCIL OF THE SCIENTIFIC RESEARCH IN UNIVERSITIES (CNCSIS), BUCHAREST, ROMANIA

DIRECTOR DE PROIECT:       Dr. Toma OCTAVIAN
PROJECT MANAGER:           Dr. Toma OCTAVIAN
Email: octavian.toma@inflpr.ro

 

DURATA PROIECTULUI:            2010 - 2012
CONDUCATOR PROIECT:          INSTITUTUL NATIONAL DE CERCETARE-DEZVOLTARE PENTRU FIZICA LASERILOR, PLASMEI SI RADIATIEI INFLPR DIN BUCURESTI

OBIECTIVE
I.1 Determinarea limitei de solubilitate a erbiului in cristalele partial dezordonate LGT, LGN si CLNGG
I.1.1 Cresterea monocristalelor de LGT, LGN, CLNGG, dopate cu erbiu in diverse concentratii, prin metoda Czochralski.
I.1.2 Caracterizarea structurala a acestor cristale dopate cu erbiu in diverse concentratii prin difractie de raze X; determinarea concentratiei de dopant pentru care structura cristalului gazda sufera modificari.

II.1 Caracterizarea spectroscopica a cristalelor partial dezordonate dopate cu erbiu
II.1.1 Determinarea nivelelor de energie ale ionului Er³⁺ in diverse cristale partial dezordonate.
II.1.2 Determinarea timpilor de viata ai nivelelor excitate ale Er³⁺ care influenteaza conversia radiatiei.
II.1.3 Masurarea sectiunilor eficace ale proceselor de absorbtie din starea fundamentala.

II.2 Caracterizarea proceselor de up-conversie prin absorbtii succesive in cristale partial dezordonate dopate cu erbiu
II.2.1 Elaborarea unui lant de masura spectroscopic pentru spectre de absorbtie din stare excitata.
II.2.2 Determinarea sectiunilor eficace de absorbtie ale proceselor de absorbtie din stari excitate care influenteaza populatia nivelului ⁴I_11/2.

II.3 Caracterizarea proceselor de transfer de energie in cristale partial dezordonate dopate cu erbiu
II.3.1 Determinarea parametrilor microscopici ai proceselor de transfer de energie prin calcularea gradului de suprapunere intre spectrele de emisie si absorbtie ale tranzitiilor implicate in transferul de energie.
II.3.2 Determinarea parametrilor macroscopici ai proceselor de transfer de energie folosind curbele de dezexcitare luminescenta a nivelelor excitate ale Er³⁺.

III.1 Optimizarea conversiei radiatiei solare din banda 1.4 – 1.8 mm in radiatie de lungime de unda in jur de 1 mm
III.1.1 Elaborarea unui model matematic care sa includa toate procesele ce influenteaza populatia nivelului ⁴I_11/2.
III.1.2 Compararea performantelor cristalelor ca up-convertori.

OBJECTIVES
I.1 Finding of the solubility limit of erbium in the partially disordered crystals LGT, LGN and CLNGG
I.1.1 Growth of the single crystals LGT, LGN, CLNGG, doped with erbium in various concentrations, using the Czochralski method.
I.1.2 Structural characterization of these erbium-doped crystals by X-ray diffraction.

II.1 Spectroscopic characterization of the erbium-doped partially disordered crystals
II.1.1 Identification of the energy levels of the Er³⁺ ion in various partially disordered crystals.
II.1.2 Measurements of the lifetimes of the Er³⁺ excited levels that influence the conversion of the solar radiation.
II.1.3 The measurement of the cross sections of the ground-state absorption processes.

II.2. Characterization of the up-conversion processes based on excited-state absorption in the erbium-doped partially disordered crystals
II.2.1 Elaboration of a spectroscopic measurement chain for the excited-state absorption spectra.
II.2.2 Measurement of the cross sections of the excited-state absorption processes that influence the population of level ⁴I_11/2.

II.3. Characterization of the energy-transfer processes in the erbium-doped partially disordered crystals
II.3.1 Finding the microscopic parameters of the energy transfer processes by the calculation of the superposition between the emission and absorption spectra of the transitions participating in the energy transfer.
II.3.2 Measurement of the macroscopic parameters of the energy transfer processes using the decay curves of the excited levels of Er³⁺.

III.1. Optimization of the conversion of the solar energy emitted in the 1.4 – 1.8 mm band in radiation of wavelength around 1 mm
III.1.1 Elaboration of a mathematical model including all processes that influence the population of the ⁴I_11/2 level.
III.1.2 Comparison of the up-converting performances of the investigated crystals.

REZULTATE
Obiectivul I.1: Determinarea limitei de solubilitate a erbiului in cristalele partial dezordonate LGT, LGN si CLNGG
Activitati
I.1.1 Au fost crescute cristale de LGT, LGN si CLNGG dopate cu ioni de erbiu in diverse concentratii, prin metoda Czochralski.
I.1.2 Au fost investigate prin difractie de raze X cristalele crescute. Limita de solubilitate a erbiului in cele trei cristale a fost determinata ca avand valorile 5%, 3% si 100%, respectiv (procente atomice).
A fost sintetizat un material cristalin nou, granatul de erbiu, litiu, calciu si galiu (ErLNGG), obtinut prin substituirea completa in CLNGG a ionilor Ca²⁺ cu Er³⁺.

Obiectivul II.1: Caracterizarea spectroscopica a cristalelor partial dezordonate dopate cu erbiu
Activitati
I.1.1 Au fost determinate nivele de energie ale Er³⁺ in diverse cristale partial dezordonate.
II.1.2 Au fost determinati timpii de viata ai nivelelor excitate ale Er³⁺ care influenteaza conversia radiatiei.
II.1.3 Au fost masurate sectiunile de absorbtie ale proceselor de absorbtie din starea fundamentala.

Obiectivul II.2: Caracterizarea proceselor de up-conversie prin absorbtii succesive in cristale partial dezordonate dopate cu erbiu
Activitati
II.2.1 A fost elaborat un lant de masura spectroscopic pentru spectre de absorbtie din stare excitata.
III.2.2 Au fost determinate sectiuni eficace de absorbtie ale proceselor de absorbtie din stari excitate care influenteaza populatia nivelului ⁴I_11/2.

Obiectivul II.3: Caracterizarea proceselor de transfer de energie in cristale partial dezordonate dopate cu erbiu
Activitati
II.3.1 Au fost determinati parametrii microscopici ai proceselor de transfer de energie prin calcularea gradului de suprapunere intre spectrele de emisie si absorbtie ale tranzitiilor implicate in transferul de energie.
II.3.2 Au fost determinati parametri macroscopici ai proceselor de transfer de energie folosind curbele de dezexcitare luminescenta a nivelelor excitate ale Er³⁺.

Modul de diseminare a rezultatelor

Lucrari publicate sau in curs de publicare in reviste cotate ISI
1. O. Toma, L. Gheorghe, and A.M. Vlaicu, “Synthesis and preliminary characterization of erbium lithium niobium gallium garnet,” Rom. J. Phys. 56 (7-8), 928-934 (2011).

2. O. Toma, L. Gheorghe, and A. M. Vlaicu, "Synthesis and Characterization of Erbium Lithium Niobium Gallium Garnet", Acta Physica Polonica A 121 (1), 193-195 (2012)

Comunicari la conferinte internationale
1. O. Toma, L. Gheorghe, and A.M. Vlaicu, “Synthesis and characterization of erbium lithium niobium gallium garnet,” International Conference APMAS (Advances in Applied Physics and Materials Science),
Antalya, Turcia, 12-15 Mai 2011.
2. O. Toma and S. Georgescu, “Modeling of two-wavelengths emission in an erbium upconversion laser," International Conference APMAS (Advances in Applied Physics and Materials Science),
Antalya, Turcia, 12-15 Mai 2011.
3. O. Toma, L. Gheorghe, and R. Birjega, "Solubility limits of erbium in partially disordered crystals langanite and langatate", 12th International Balkan Workshop on Applied Physics, Constanta,
Romania, 6-8 Iulie 2011.