Luminescence

Theory and Applications of Rare Earth Activated Phosphors

Ratnesh Tiwari, Vikas Dubey, Vijay Singh, María Elena Zayas Saucedo, Ratnesh Tiwari, Vikas Dubey, Vijay Singh, María Elena Zayas Saucedo

• Éditeur: De Gruyter
• Année: 2021
• ISBN:
  9783110676518
• Édition: 1
• Sujet: Scienze fisiche
• Sous-sujet: Chimica inorganica

Phosphors are often consisting of transition-metal compounds or rare-earth compounds, with the most common application being displays and fluorescent light. This book will guide the reader through the latest developments in thermo-, electro-, mechano- and bioluminescence of rare earth phosphors and crystals. Also, the effect of doping will be discussed.

Chapter 1 Recent Progresses in the Development of Luminescent Lanthanide-Based Hybrid Entities and Their Applications

Ratnesh Das

Sneha Wankar

Imran Khan

Abstract

This chapter concentrates predominantly on the recent trends in fabrication and synthesis of luminescent lanthanide hybrids. It also unveils the detailed insight of energy transfer mechanism that proceeds in fundamental lanthanide organic complexes. To achieve the advancement in the basic property of lanthanide complexes in terms of enhanced mechanical strength, better temperature tolerance, desired photophysical properties, synthesized lanthanide complexes are specifically embedded or bonded with organic/inorganic matrix. In this milieu, the synthetic approaches that deal with advance methodologies were taken into consideration. Supplementarily, the application of such advance materials in the real world is profoundly documented in detail.

Keywords: lanthanide ions, TESPIC, ORMOSILs, silica, beta-diketone, mesoporous hybrid,

1.1 Introduction

Lanthanide complexes are adeptly beneficial in photonics by virtue of their multifaceted photophysical properties [8] that are markedly relevant to their adoption in fabrication of highly energetic phosphors [47]. They are also projecting themselves as lasers, namely, yttrium aluminum garnet (YAG) [133]. Their relevance in the materials is viable for light amplification, highly efficient optical light-emitting diodes (LEDs), modeling of various electronic displays, imaging of cell organelles, selective sensing of various ions which are important biologically and also environmentally in immunoassays and utilization in medical field [50, 91, 101]. In accordance with IUPAC, elements from cerium to lutetium are entitled as lanthanide series; their electronic configuration is 4f^N where N = 1–14, and their electronic configuration is featured with +3 oxidation state [82]. The luminescent behavior of lanthanides corresponds to operative transition in terms of d–f transitions (allowed) or reorganization of electrons in the 4f shell and appears as f–f transition. The nature of d–f transitions is highly energetic and intense over f–f transition, which is not allowed according to Laporte’s selection rule. However, it is allowed under the magnetic dipole–induced transition, and the emission intensity is feeble in nature. The disposition of 4f shell is completely shielded away from outer environment by 5s² and 5p⁶ shells. When these lanthanide ions coordinated with ligands containing oxygen or nitrogen, the electronic configuration get perturb. The shielded 4f orbitals appear with the unique emission property ranging from visible to near-infrared (NIR) region, longer lifetime of excited state. The position of the emission band of the lanthanide complexes depends on the nature of the ligand and the wavelength of excitation. The resultant luminescence is perceived by means of divergent source of excitation. Thus, few of them listed as excitation by means of electromagnetic radiation show photoluminescence, influenced by electric field resulted in electroluminescence, applied mechanical stress to give rise to triboluminescence, finally chemiluminescence is obtained because of chemical reactions. The concept of crystal field splitting came to an existence with the help of theoretical calculations and atomic quantum theory.

Keywords: lanthanide, photophysical, magnetic dipole, crystal field

Interestingly, furthermore, crystal-field effects are extremely accountable for the ease of selection rule, and thus additional lines broaden some components of the spectral lines. In the first instance, Judd and Ofelt in 1962 [46, 86] streamlined the studies on the intensities of transitions, then secondly, Wybourne well tried to measure the energies up to certain level [20, 137]. These researchers subsequently assigned all electronic sublevels that fall below energy amounted to 40,000 cm⁻¹ (250 nm), and the calculated energy levels were molded into very well-known Dieke’s diagram. The soundness of lanthanide spectroscopy constitutes bunch of electronic levels brought about by various electronic configurations assigned to 4f^N and 4f^N–5d¹. Taking this into consideration, the noteworthy splitting of crystal field in lower symmetry of electronic levels of trivalent La–Lu is equated to 16,384 for 4f^N, whereas 180,199 for f^N–1d¹ configurations. Figure 1.1 demonstrates SLJ electronic levels for previously mentioned electronic levels that markedly considered as higher than 50,000 cm⁻¹. An acronym SLJ implies three quantum numbers where S = ½ multiplied by the number of unpaired present in f-orbital, then L stands for total angular momentum while S is represented as total spin number and can be calculated as S = ½ multiplied by the number of unpaired electrons present in f-orbital. Thus, the total spin–orbit quantum number J can be calculated as [J = from (L + S), (L + S – 1) to (L – S)] [10, 11]. According to Laporte’s selection rule, the intraconfigurational transitions are not allowed, and spin rule states that the spin state of electrons must not alter in an optical transition. However, the selection rules are somehow relaxed because of mixing of various wave functions, including vibrational functions. Thus, the resultant f–f transitions are allowed and termed as forced electric dipole transition. In 1953, an eminent worker Dexter [19] has proven that the energy transfer proceeds, which genuinely depends on the distance between donor and acceptor molecules. This work was further expanded by Förster in 1948 [30], referring to the dipole–dipole energy transfer process; apart from this, the three major contributions were identified as follows: electric dipole–dipole transition, electric dipole–quadrupole transition and spin exchange, while electric quadrupole–quadrupole and el...