Ultraviolet (UV) light, consisting of high energy photons, is useful for wide range of applications. However, natural sunlight contains only ca. 4 % of UV photons in overall photons, and this aspect has been limiting the utility of natural sunlight for UV-necessitating purposes. Photon upconversion (UC) converts lower energy photons (i.e., longer wavelength light) to higher energy photons (i.e., shorter wavelength light). Recently, studies of UC based on triplet-triplet annihilation (TTA) are becoming active because of its applicability to an incident light with low intensity. While majority of previous studies used liquid solutions, development of solid-state samples has been pursued recently. However, previous solid samples were often microcrystals with very small crystal domains containing large number of disorders, resulted in a poor transport of triplet excited state in the materials and a substantially lowered rate and probability of TTA. Recently, we have developed a novel method to form UV-UC films from a melt utilizing temperature gradient on a substrate. Although this technology generated efficient UV-UC films, the effects of many parameters involved there have not been understood well. Therefore, to further improve the performance of the films, we especially investigated the effect of cooling rate on the crystallinity as well as properties of the films. Consequently, we revealed an importance of optimally choosing the cooling rate. It was also found that the crystallinity decreased when a large temperature difference existed between the top and bottom of the substrate.