Luminescence Properties of Co-doped Eu3+, Bi3+ Lu2O3/Polyvinylpyrrolidone Films

Ángel De Jesús Morales-Ramírez,Joan Reyes-Miranda,Fernando Juárez-López,Dulce Yolotzin Medina-Velázquez,Margarita García-Hernández,María Del Rosario Ruiz-Guerrero

doi:10.3390/coatings8120434

Abstract

The effect of the polyvinylpyrrolidone (PVP, MW = 130,000) molar content, PVP/Lu = 1, 2.5, 4 and 5; on the photoluminescent and structural properties of sol-gel derived Lu2O3:Eu3+, Bi3+ has been analyzed. Thin hybrid films were deposited by means of the dip-coating technique on silica quartz substrates. Films deposited at 700 °C presented a cubic structure, with non-preferential orientation, even with the presence of PVP. The photoluminescence (PL) spectrum and Comission Internationale de l’Éclairage (CIE) chromaticity diagram of films revealed a reddish Eu3+ emission at 612 nm (5D0 →7F2) with an excitation at 320 nm of the Bi ions (6s2→6s6p), showing a highly-effective energy transfer process form Bi3+ to Eu3+ luminescent centers. On the other hand, the color temperature of the samples is strongly dependent on the PVP content, as a consequence of the observed difference on the branching ratios of 5D0 →7FJ transitions of europium ions. Lifetime studies present two different behaviors for the thin films: A non-exponential nature for the lower PVP contents, and a simple exponential nature for the highest PVP one, showing that the PVP tends to promote a better dissolution of segregates and, therefore, increases the lifetime of the Eu3+ emission.

Highlights

The design of new functional hybrid films had an extended development in the last years due their new properties as a result of the addition of an organic to an inorganic film that combine the properties of both materials [1,2,3,4,5]
This bismuth content was selected as a result of our previous work [37] where it analyzed the effect of the bismuth concentration on the photoluminescent properties of Lu2 O3 :Eu3+, Bi3+ powders, showing that the highest emission intensity was at Bi3+ 1 mol.%
It is important to notice that, using the present methodology, the sample containing a molar ratio of PVP/Lu = 5 possessed the largest amount of PVP which the system could dissolve without losing the stability of the sol

Summary

Introduction

The design of new functional hybrid films had an extended development in the last years due their new properties as a result of the addition of an organic to an inorganic film that combine the properties of both materials [1,2,3,4,5]. Due to polymeric properties, the hybrid films are “softer” and more flexible in their structure of all inorganic films that produce crack-free hybrid films. In this way many complexes, like citric acid (CA) ethylenediame tetra-acetic acid (EDTA), ethylene glycol (EG), triethylenetetramine (TETA) and polyvinylpyrrolidone (PVP), were studied in order to develop new materials [6,7]. Coatings 2018, 8, 434 been great interests in the thin films preparation of phosphors with improved physical and emissive properties. The cubic sesquioxides (R2 O3 , R = Lu, Gd, Ln, etc.) present high thermal conductivity, physical and chemical stability, optical properties (low phonons) and the possibility of doping with

Methods

Results

Conclusion