Gin Jose

Sensitized fluorescence of Ce3+/Mn2+ system in phosphate glass

Abstract The preparation of sodium phosphate glasses singly and doubly doped with rare earth ion Ce 3+ and transition metal ion Mn 2+ by a melt quench method is described. The spectroscopic characterizations of the samples are conducted by absorption, excitation, and emission spectra. The orange red emission of divalent manganese sensitized by trivalent cerium ions in a phosphate glassy matrix has been investigated. Energy transfer (ET) from optically excited Ce 3+ to Mn 2+ in sodium phosphate glass, by nonradiative process is confirmed by fluorescence studies with various activator concentrations. The mechanism of ET is mainly electric dipole–dipole in nature.

Energy transfer in Sm3+:Eu3+ system in zinc sodium phosphate glasses

The mechanism of nonradiative energy transfer process in zinc sodium phosphate glass system co-doped with samarium and europium ion has been examined under cw laser excitation. Donor–acceptor distance and quantum efficiency of transfer have been evaluated using the relevant theoretical expressions. Transfer probabilities have been determined using the overlap integral and relative fluorescence methods. The Forster–Dexter theoretical predictions are found to be in excellent agreement with experimental results. The nonresonant energy transfer assisted by phonons is the dominant transfer mechanism in the concentration range taken. Excitation spectra and the decay profile of the samarium ion also support the energy transfer from samarium to europium.

Judd–Ofelt intensity parameters and laser analysis of Pr3+ doped phosphate glasses sensitized by Mn2+ ions

Abstract In this paper, we report the preparation and optical characterization of Mn2+ activated Pr3+ doped phosphate glasses in four different chemical compositions. The optical absorption spectra of Pr3+ ions in phosphate glasses have been recorded in the UV–VIS–NIR region. From the data available in the optical absorption spectra, various spectroscopic parameters such as Slater–Condon (F2, F4, F6), Racah (E1, E2, E3), spin-orbit interaction (ξ4f) and Judd–Ofelt (J–O) (Ω2, Ω4, Ω6) parameters are derived. The calculated values of the J–O parameters are utilized in evaluating the various radiative parameters such as electric dipole line strengths (Sed), magnetic dipole line strengths (Smd), radiative transition probabilities (ARAD), radiative lifetimes (τRAD), fluorescence branching ratios (βR) and the integrated absorption cross-sections (σa) for stimulated emission from various excited states of Pr3+ ion. The principal fluorescence transitions of interest are identified by recording the fluorescence spectrum and measuring their stimulated emission cross-section and optical gain. Quantum efficiencies of the prominent lasing transitions are estimated by measuring their radiative and fluorescence lifetimes. The dependence of effective radiative lifetime on Pr3+ ion concentration is discussed in the light of non-radiative processes such as multiphonon relaxation and energy transfer between like and unlike ions.

NIR to UV absorption spectra and the optical constants of phthalocyanines in glassy medium

Optical absorption studies of phthalocyanines (Pc-s) in borate glass matrix have been reported for the first time. Measurements have been done corresponding to photon energies between 1.1 and 6.2 eV for free base, manganese, iron, nickel, molybdenum, cobalt and copper phthalocyanines. Several new discrete transitions are observed in the UV-vis region of the spectra in addition to a strong continuum component of absorption in the IR region. Values of some of the important optical constants viz. absorption coefficient (alpha), molar extinction coefficient (epsilon), absorption cross-section (sigma(a)), band width (delta lambda), electric dipole strength (q2) and oscillator strength (f) for the relevant electronic transitions are also presented. All the data reported for Pc-s in the new matrix have been compared with those corresponding to solution, vapor and thin film media.

Application of a modified Judd–Ofelt theory to Pr3+ doped phosphate glasses and the evaluation of radiative properties

Abstract Kornieko et al.’s [Phys. Stat. Sol. (B) 157 (1990) 267] modified version of the Judd–Ofelt (J–O) theory has been used to evaluate the oscillator strengths and radiative lifetimes of Pr 3+ in a series of phosphate glasses. The results are compared with those obtained from the original J–O theory in our previous work [J. Non-Cryst. Solids 275 (2000) 93]. Experimental and theoretical oscillator strengths are presented and J–O parameters are determined by both methods for all glasses. The calculated radiative lifetimes are compared with the experimentally measured values for the 1 D 2 energy level and the suitability of the two models are compared. Results show that the modified theory provides better agreement with the experimentally measured lifetimes of the 1 D 2 transition.

Spectroscopic studies of Cu2+ ions in sol-gel derived silica matrix

The Cu2+ ion doped silica gel matrices in monolithic shape were prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS). The absorption, transmittance and fluorescence spectra of the gel matrices heat treated at different temperatures were monitored. The loss of water and hydroxyl group from silica network changes the optical properties of the Cu2+ ions in the host, noted by the change in colour of monolith and spectral characteristics. The pronounced blue shift observed (700–900 nm to 600–850 nm) for the broad band of the absorption spectra of the samples heated up to 700°C is attributed to the ligand field splitting and partial removal of hydroxyl group from the silica matrices. The results indicate broadband filtering effects of the samples in the wavelength region 400–600 nm. Absorption and fluorescence spectra of the glass matrices heated to 1000°C confirms the conversion of Cu2+ ion to Cu+ ion.

Fluorescence enhancement from Eu3+ ions in CdSe nanocrystal containing silica matrix hosts

Abstract Semiconductor cadmium selenide particles together with europium ions were incorporated into the silica matrix using sol–gel method. Here, the effect of nanocrystals on the absorption and fluorescence features of europium ions is discussed. The fluorescence spectra reveal that the intensity of characteristic emission of europium increases considerably in the presence of CdSe particles. This phenomenon can be explained as due to the energy transfer resulting from electron–hole recombination in the CdSe to the rare earth ion. These zero-dimensional materials, along with the effect of matrix incorporating europium ions, are found to have increased the optical gain.

Optical properties of porphyrins in borate glassy matrix

Optical properties of free and substituted porphyrins (PP) doped borate glass matrix are reported for the first time. Absorption spectral !l5urernents of H2 TPP, CdTPP, MgTPP and ZnTPP doped borate glass matrix have been made in the 200-1100 nm region and the :l:traobtained are analyzed to obtain the optical bandgap (Eg) and other important spectral parameters viz. oscillator strength (f), molar :Iinction coefficient (e), electric dipole strength (l), absorption cross-section (a.) and molecular concentration (N). Intense fluorescence ~observed in the region 668-685 nm for CdTPP, ZnTPP and MgTPP doped matrices, whereas no such fluorescence was observed in ~TPP doped matrix. Fluorescence intensity was observed to be almost similar in all the metallated porphyrine matrices. Fluorescence mdwidth (~)..), decay time (r), stimulated emission cross-section (a) and optical gain (G) of the principal fluorescence transitions iUesponding to the Q-band excitation were also evaluated and discussed.

Spectroscopic studies of Sm3+-doped phosphate glasses

Optical properties of Sm3+ ion in phosphate glassy matrices were studied. The absorption, fluorescence, excitation spectra and decay patterns were obtained at room temperature. The oscillator strengths of the transitions betweenJ manifolds were calculated using Judd-Ofelt theory and compared with the ones obtained experimentally. Various laser intensity parameters such as J-O parameters, radiative transition probabilities, lifetimes, branching ratio, and integrated absorption cross-section were evaluated. Radiative lifetimes of the excited states were determined and used to obtain nonradiative transition rates and quantum yields. Integrated intensity and dynamics of the fluorescence originating from the excited states were also studied as a function of Sm3+ concentration.

Emission spectral studies of phthalocyanines in borate glass matrix

Organic semiconductors play a very important role in today’s high technology applications viz. optical imaging, optical switchng, optical computing, data storage, photodynamic therapy, dynamic holography, frequency mixing, harmonic generation and optical communications [1–4]. Among the organic semiconductors the phthalocyanines (Pc), naphthalocyanines (Nc) and porphyrines (PP) are of special significance because of their inexpensiveness, thermal and environmental stability, non toxicity as well as excellent optical and electronic properties. A combination of these features makes them an important class of photo-electronic materials for applications in various optoelectronic devices. Moreover, because of their excellent optical absorption efficiency in the red or NIR region they can be effectively utilized as a laser dye also. Most of the studies reported so far discuss the optical characterization of these organic semiconductors either in thin films, crystals, vapor or other solvents [4] whereas no work has been made to study the optical properties of these molecules in solid matrices especially work has been made to study the optical properties of these molecules in solid matrices especially a glassy matrix. Except for some studies in certain organic glassy matrices [5] only a limited amount of work has been done in organic matrices also. Recently our group has synthesized borate glassy matrices doped with metalatted phthalocyanines and rare earth doped phthalocyanines and studied their optical absorption characteristics [6, 7] The purpose of the present communication which is a continuation of the earlier work is to study the stimulated emission characterstics of metalatted phthalocyanine molecules in borate glass matrix with the intention of using them as efficient active media for solid state lasers. All the glass samples were prepared by the well known rapid quenching technique [8]. Reagent grade boric acid (H3BO3) and doubly sublimed phthalocyanines have been used as the starting materials for the preparation of the glass samples. The weighed quantities of the starting materials for 18 gm of glass were mixed homogeneously using an agate mortar. The batch was then placed in a silica crucible and heated in an electric muffle furnace. A slow heating was initially maintained until the temperature reached 80 ◦C and decomposition of H3BO3 to B2O3 was complete. The temperature was then rapidly increased to 120 ◦C so as to obtain a bluish melt. The melt was retained for about 10 min and then rapidly quenched by placing in between two well polished preheated brass plates so as to obtain glass discs of about 3 mm thickness and with a diameter of about 2 cm. The glass discs thus obtained were annealed at a temperature of about 60 ◦C and subsequently polished with water free lubricants. All the samples were obtained with very good transparency and appeared to be of good optical quality. Glass rods of length 8 cm, having diameter of 2 cm were also developed by heating the starting chemicals in 75 cm long borosil glass tubes after providing the necessary vacuum using a rotary pump. To remove the water vapor originating as a result of the decomposition of H3BO3 a vacuum trap was provided in between the rotary inlet and the sample tube. The tube was kept in a 1 m long vertical heater, the temperature of which can be controlled externally. After melting, the heater was switched off and the melt allowed to cool to room temperature by keeping it inside the heater itself. Finally the tube was taken out and glass rod removed by breaking the glass tube. The amorphous nature of the glass samples were confirmed by X-ray diffraction spectra recorded on a Shimadzu X-ray diffractometer with Ni filtered Cu Kα radiation. The absorption spectra were recorded in the UV-VIS-NIR region with a Hitachi U-2000 spectrophotometer. All the emission spectra were recorded at room temperature using a SPEX spectrofluorimeter with a wavelength resolution of ±0.2 nm. In all the fluorescence measurements the samples were excited at two wavelengths viz. 330 nm (corresponding to B band) and 700 nm (corresponding to Q band). Figs 1 to 8 show the fluorescence spectra of various Pc doped glassy matrices. All the other spectral data viz. emission wavelength, fluorescence bandwidth, relative fluorescence intensity, decay time and stimulated emission cross section are summarized in Table I. If we plot the absorption spectra of all these samples [6] and the corresponding emission spectra in the same plot it can be easily noted that the fluorescence spectra is almost the mirror image of the absorption lineshape as is observed in other matrices viz. crystals, vapors and other solvents [9–11]. Because of this “mirror image fluorescence” we can apply the Stickler-Berg formula [12] for evaluating the fluorescence decay time (τ ) and the expression is given by