Transparent Oxyfluoride Nano-Glass Ceramics Doped with Pr3+ and Pr3+–Yb3+ for NIR Emission

Abstract

Pr 3+-Yb 3+ co-doped oxyfluoride glasses and glass-ceramics (GCs) containing LaF3 nanocrystals have been prepared to obtain NIR emission of Yb 3+ ions upon Pr 3+ excitation in the blue region of the visible spectrum. Two different compositions have been tested: 0.1-0.5 Pr-Yb and 0.5-1 Pr-Yb, in addition to Pr 3+ singly doped samples. The crystallization mechanism of the nano-GCs was studied by differential thermal analysis revealing that it occurs from a constant number of nuclei, the crystal growth being limited by diffusion. High-resolution transmission microscopy demonstrated that phase separation acts as precursor for LaF3 crystallization and a detailed analysis of the chemical composition (EDXS) revealed the enrichment in RE 3+ ions inside the initial phase separated droplets, from which the LaF3 crystals are formed. The RE 3+ ions incorporation inside LaF3 crystals was also proved by photoluminescence measurements showing Stark splitting of the RE 3+ ions energy levels in the glass-ceramic samples. Lifetime measurements showed the existence of a better energy transfer process between Pr 3+ and Yb 3+ ions in the GCs compared to the as made glass. The highest value of energy transfer efficiency is 59% and the highest theoretical quantum efficiency is 159%, obtained for GCs 0.1-0.5 Pr-Yb treated at 620°C for 40 h.Keywords: transparent, glass-ceramics, rare-earths, crystallization, down-conversion, solar energy inTrODUcTiOn Solar green energy is one of the emerging fields where rare earth (RE) ions are intensively used to improve silicon solar cells (SSCs) efficiency. In fact, the most important routes to reduce costs and promote the use of solar energy are: decrease refining and crystallization cost of silicon (the most widely used semiconductor), to use less silicon (thinner cells), developing thin films solar cells of less expensive materials (organic, polymeric) and/or improving SSCs efficiency.Currently, many efforts are focused in the modification of the photovoltaic (PV) cells to make them more efficient. The main problem to improve PV energy conversion efficiency is associated with the spectral mismatch between the energy distribution of photons in the incident solar spectrum and the band-gap of silicon (Huang et al., 2013). Therefore, in the last years, solar down-converter materials doped with RE ions, able to convert the blue part of the solar spectrum to the range 980-1050 nm, where silicon presents the best response, are becoming increasingly important (Trupe et al., 2002;Richards, 2006;van der Ende et al., 2009). According to Abrams et al. (2011), a theoretical improvement of SSCs could be as high as 7% for an ideal lossless system; however, improvements (even though smaller than 7%) could be reached with a properly engineered solar converter layer.Among the converter materials, glasses and glass-ceramics (GCs) for PV application are increasingly important thanks to their relatively easy production and engineering and their capability of hosting a great variety of RE ions in different concentrati...

A Comparative Study on Luminescence Properties of Y2O3: Pr3+ Nanocrystals Prepared by Different Synthesis Methods

“…Specifically, rare-earth doped nanocrystals (RE NCs) have drawn remarkable attention in the past few decades due to their singular properties such as high photostability, narrow emission lines, long fluorescence lifetimes, and easy functionalization [1,2]. As a result, a wide variety of applications has arisen in different fields, including medicine [3] and biology [4], solar energy [5], data storage [6], and optoelectronics [7]. Amid all the aforementioned fields, optics could be considered the most popular one due to the noteworthy number of applications, like fiber lasers and amplifiers [8], cathode ray tubes [9], plasma display panels [10], field emission displays [11], or fluorescence lamps [12] to name a few.…”

Effect of Partial Crystallization on the Structural and Luminescence Properties of Er3+-Doped Phosphate Glasses

“…Recently, GCs have been further investigated because their luminescence properties may be increased by the crystalline environment around the RE ions [20,21,22,23]. Yu et al [24,25] reported an increase of about two orders of magnitude in the emission intensity of the Er 3+ /Yb 3+ co-doped phosphate GCs compared to the correspondent as prepared glasses.…”

80SiO2‐20LaF3 oxyfluoride glass ceramic coatings doped with Nd3+ for optical applications

“…Many oxyfluoride GCs have been prepared by the melting quenching (MQ) method 10,11 using several RE ions, as Eu 3+ , 12 Nd 3+ for its use as laser material at 1.06 lm, [13][14][15] Pr 3+ -Yb 3+ as down-converter materials, [16][17][18] and Er 3+ -Yb 3+ for up-conversion. 19,20 But MQ method presents some limitations such as the high temperature of processing that causes fluorine loss by evaporation.…”